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SONOGRAPHIC DETERMINATION OF OPTIC NERVE
SHEATH DIAMETER AND LENS THICKNESS IN
GLAUCOMA PATIENTS AT THE OAUTHC ILE-IFE.
BY
DR OMATIGA Achimugu Gabriel
(MB:BS, IBADAN)
A DISSERTATION SUBMITTED TO THE FACULTY OF
RADIOLOGY, NATIONAL POST GRADUATE MEDICAL COLLEGE
OF NIGERIA IN PARTIAL FULFILMENT FOR THE AWARD OF THE
FELLOWSHIP IN RADIOLOGY
(FMCR)
NOVEMBER 2016
ii
ATTESTATION
I, Dr Omatiga Achimugu Gabriel attest that this dissertation is my original work which was
carried out at the Obafemi Awolowo University Teaching Hospital Complex, Ile-Ife, Osun
state.
……………………………………………………………………………………………..
Dr Omatiga Achimugu Gabriel
Obafemi Awolowo University Teaching Hospital Complex, Ile-Ife,
Osun State.
iii
CERTIFICATION
I certify that this dissertation represents the original work of Dr Omatiga Achimugu Gabriel
and that it was done during his residency program at the department of Radiology Obafemi
Awolowo University Teaching Hospital Complex, Ile-Ife, Osun State.
Dr O C FAMUREWA (FWACS)
Head, Radiology Department
Obafemi Awolowo University Teaching Hospital Complex
Ile-Ife.
iv
ATTESTATION
We attest that this dissertation represents the original work of Dr Omatiga Achimugu
Gabriel which was done during his residency program at the Department of Radiology,
Obafemi Awolowo University Teaching Hospital Complex, Ile-Ife and that it was supervised
and reviewed by us.
------------------------------------------------- ---------------------------------------------------
Dr O. O AYOOLA (MBChB, FMCR) DR O. H ONAKPOYA (FWACS, FMCOph)
Consultant Radiologist Consultant Ophthalmologist
Obafemi Awolowo University Obafemi Awolowo University
Teaching Hospital Complex Teaching Hospital Complex
v
Ile-ife. Ile-ife.
ACKNOWLEDGEMENT
My unreserved appreciation goes to God for His unfailing help. Special appreciations to
my supervisors, Dr O.O. Ayoola and Dr O.H Onakpoya. I appreciate and I am grateful to my
Head of Department Dr (Mrs) O.C. Famurewa. I also want to appreciate my teachers and
Consultants, Prof V.A Adetiloye, Dr (Mrs) C.M. Asaleye and Dr B.O. Ibitoye.
I am also grateful to all my colleagues and staff of the Department of Radiology especially Dr
Aderibigbe and the residents of the Department of ophthalmology, Obafemi Awolowo
University Teaching Hospital Complex for the invaluable assistance they rendered to me.
To Dr Simi Agbeleye, i am immensely grateful for your support and assistance.
vi
DEDICATION
I dedicate this work to my Heavenly Father who has been my Light and Guide at all times, to
my beautiful wife Idia Dawn Omatiga and our lovely Daughter Eleojo Isabel Omatiga, you are
the driving force in my life, God bless you. Also to the memory of my late dad Mr Isaac
Omatiga who sacrificed a lot for us to make a success of our lives.
vii
TABLE OF CONTENT
Title page i
Attestation
ii
Certification
iii
Attestation
iv
Acknowledgement
v
Dedication
vi
Table of contents
vii
List of abbreviations ix
List of figures
x
List of tables
xi
Summary 1
Introduction
3
Aims & Objectives
5
Justification
6
Gross anatomy
8
Sonographic anatomy
12
viii
Literature review
16
Materials and method
26
Ethical considerations
33
Results
34
Discussion 51
Limitation 55
Conclusion 56
Recommendation 57
References 58
Appendices 62
Subject information sheet 62
Consent form 64
Ethical clearance 65
Questionnaire 66
ix
LIST OF ABREVIATIONS
OAUTHC Obafemi Awolowo University Teaching Hospitals Complex
ONSD Optic Nerve Sheath Diameter
LT Lens Thickness
POAG Primary Open Angle Glaucoma
IOP Intraocular Pressure
OAG Open Angle Glaucoma
WHO World Health Organisation
BP Blood Pressure
CCT Central Corneal Thickness
NVG Neurovascular Glaucoma
SSA Sub-Sahara Africa
LDF Laser Doppler Flowmetry
C/D Cup Disc Ratio
ECM Extra Cellular Matrix
MRI Magnetic Resonance Imaging
CSF Cerebro-Spinal Fluid
MHZ Mega Hertz
SPSS Statistical Package for Social Sciences
BMI Body Mass Index
FBG Fasting Blood Glucose
DBP Diastolic Blood Pressure
x
ACG Angle Closure Glaucoma
RLT Right Lens Thickness
NTG Normal Tension Glaucoma
RNFL Retina Nerve Fibre Layer
LIST OF FIGURES
Fig. 1: A schematic diagrams of the anatomy of the eye and sonographic 10
Anatomy showing the anterior segment structures in A, and the posterior
segment structures in B
Fig 2: A schematic diagram of the human eye, showing the optic 11
nerve and the lens.
Fig. 3: A sonographic Anatomy of the Optic Nerve Axial section 14
Fig.4. Sonographic Anatomy of the Lens. 15
Fig. 5: Sonographic measurement of the Optic Nerve. 30
Fig. 6: Sonographic measurement of the lens thickness. 31
Fig. 7: Bar chart showing distribution of different types of glaucoma. 36
Fig. 8: A Boxplot showing the pattern of the right ONSD among glaucomatous
patients (p= 0.000). 39
Fig. 9: Boxplot showing the pattern of left ONSD among glaucomatous patients
(p =0.000) 40
Fig. 10: Boxplot showing no differences in Right lens thickness among study
participants (p = 0.109) 41
Fig. 11 Boxplot showing significantly higher Left lens thickness among Glaucoma
patients (p = 0.024) 42
xi
LIST OF TABLES
Table 1: A table showing Patients' General Characteristics 34
Table 2. A table showing the Differences in IOP, ONSD and Lens
thickness between the study groups. 37
Table 3: A table showing the Paired comparison of IOP, ONSD and Lens thickness
among study subjects 43
Table 4: A table showing, the Correlation between respondents' Age, ONSD and Lens
thickness. 45
Table 5: A table of the Regression analyses for predictors of lens thickness in
Glaucoma patients. 47
Table 6: A table showing Discordant / Regular pattern of the IOP
and ONSD 49
1
SUMMARY
BACKGROUND
Glaucoma is an optic neuropathy resulting in a characteristic appearance of the disc and a
specific pattern of irreversible visual field defect that are associated but not invariably with
raised intraocular pressure. It commonly leads to blindness if left untreated. This study was
designed to investigate the effect of glaucoma on optic nerve sheath diameter (ONSD) and Lens
thickness (LT).
AIM: This was a prospective case controlled study aimed at determining the optic nerve sheath
diameter and lens thickness among glaucoma patients using B-mode ultrasonography.
METHODS: 120 subjects were recruited, 60 glaucoma and 60 age and sex matched controls
screened by the Ophthalmologist and sent to the Radiology department of the Obafemi
Awolowo University Teaching Hospitals Complex Ile-Ife. Their ONSD and LT were measured
using linear high frequency 6.5-12MHz probe. The data acquired was analysed using SPSS
version 18.
RESULTS: The mean ONSD of the glaucomatous eyes were 3.57 ± 0.19mm and 3.59 ±
0.33mm on the right and left respectively while that for controls were 4.23 ± 0.34 mm and 4.26
± 0.30mm on the right and left respectively. The mean ONSD were statistical significantly
smaller in glaucomatous eyes than controls (p = 0.000). The (LT) of the glaucoma patients had
a mean of 4.15 ± 0.43mm and 4.18 ± 0.46mm on the right and left respectively while the controls
had a mean of 4.01 ± 0.56mm and 3.99 ± 0.45mm showing a statistically significant higher
mean LT between glaucomatous eyes and controls (p = 0.024). The Pearson correlation
coefficient between age and ONSD was negatively weak in both glaucomatous eyes at -0.230
(p = 0.077) and -0.119 (p = 0.144) for the right and left eye respectively; but was strongly
2
negative in controls at r = -0,549 and -0.548 on the right and left sides respectively (p = 0.000)
on either side. Mean intraocular pressure of both eyes of glaucoma subjects was significantly
higher than the mean for controls with glaucoma having 17.3 ± 8.1mmHg and 17.1 ± 7.6mmHg
on the right and left sides respectively and controls having 14.5 ± 3.1mmHg and 15.0 ±
3.3mmHg on the right and left respectively.
CONCLUSION: B-mode ultrasound is a reliable tool of assessing the nerve sheath diameter and
lens thickness in glaucoma. Optic nerve sheath diameter is reduced in glaucoma.
3
INTRODUCTION
Glaucoma is a devastating disease which has not been fully addressed. It is a major disease of
public health importance being a leading cause of blindness1. The suggested prevalence of
glaucoma in Sub Saharan Africa is 4% in people aged 40 years and above2.
Primary open-angle glaucoma (POAG), the most common form of glaucoma1, is a chronic,
progressive disease often, though not always, accompanied by elevated intraocular pressure
(IOP). Risk factors for glaucoma include old age, diabetes, Afro-Caribbean race, a family
history and myopia3,4. Angle-closure glaucoma also called closed-angle glaucoma; narrowangle
glaucoma, on the other hand usually occurs as an acute emergency as acute Angle closure
glaucoma. Glaucoma is predominantly open angle (OAG) in Nigeria and the rest of the West
African Sub region5.
In POAG, flow of aqueous humour is reduced through the trabecular meshwork, due to the
degeneration and obstruction of the trabecular meshwork, whose original function is to absorb
the aqueous humour. Reduced aqueous humour outflow leads to increased resistance and thus
a chronic, painless build-up of pressure in the eye. In close/narrow-angle, the iridocorneal angle
is completely closed because of forward displacement of the root of the iris against the cornea,
resulting in the inability of the aqueous fluid to flow from the posterior to the anterior chamber
and then out of the trabecular network. This accumulation of aqueous humour causes an acute
increase of pressure and pain6. The effect of the elevated IOP is mainly borne by the optic nerve
causing a characteristic optic atrophy which leads to a reduction in the ONSD. For some
unknown reasons, the LT has also been shown to be increased in close angle glaucoma
4
The imaging techniques for evaluating the optic nerve and lens biometry include
Ultrasonography, Computed Tomographic Scan and Magnetic Resonance Imaging. Ocular
sonography has been proven to be highly precise and more reliable at measuring the lens
thickness than optical measurements7. Sonographic measurement of the ONSD is also a very
effective method of investigating the optic nerve. Since the global target of WHO in Vision
2020 i.e. the “right to sight initiative” is ultimately to reduce blindness prevalence to less than
0.5% in all countries or less than 1% in any community (WHO, 2000)1,8, the government, the
public and public health officials face a big task in Nigeria.
Ultrasound when compared with the other imaging modalities, offers a non-invasive and direct
determination of the ONSD and LT in glaucomatous eyes. The measured nerve sheath thickness
correlates well with the level of axonal loss which leads to the optic atrophy seen in glaucoma.
To reduce the burden of the disease, early diagnosis and screening is important. Ocular
sonography offers quick and early assessment for glaucomatous eyes and screening for
glaucoma suspects where morphological and functional assessments are impossible.
The aim of the study was to determine the ONSD and the thickness of the lens with the aid
of ultrasound in patients with glaucoma.
5
AIM AND OBJECTIVES
BROAD AIM
To determine the ONSD and LT in subjects with glaucoma
SPECIFIC OBJECTIVES
1. To determine ONSD in Glaucoma subjects and control group
2. To determine the LT in Glaucoma subjects and control group.
3. To compare the ONSD and LT with control groups.
4. To determine the relationship between the degree of ONSD and LT with the age of
subjects.
HYPOTHESIS
Glaucoma causes a reduction in ONSD
SUBHYPOTHESIS
There is no reduction in ONSD in glaucoma
JUSTIFICATION
Glaucoma is an optic neuropathy ranking among the leading causes of acquired and
preventable blindness globally. The estimates by WHO suggest that depending on geographic
6
location, glaucoma is responsible for 5.7 to 22.7% of all blindness worldwide9. It may be fair
to estimate that around 10% of global blindness may be from glaucoma9.
Glaucoma has consistently ranked the second leading cause of blindness10-12 and the leading
cause of preventable and rather unfortunately, irreversible blindness globally11,13. The definition
of this disease continues to evolve, allowing for continual modification of detection methods,
treatment end-points and therapeutic options14. Glaucoma is traditionally assessed by the triad
of tonometry, visual field testing and optic nerve evaluation15,16. Several ocular and sometimes
non-ocular factors can however impair the usefulness of these morphological and functional
assessment variables in the evaluation of glaucoma suspects15. These factors include but are not
limited to an opaque media i.e. cataract, mental and sometimes physical limitations of patients15.
There arises a need therefore to look away from this traditional triad of assessment to a more
objective way of evaluating glaucoma, independently of IOP and optic nerve head morphology.
The optic nerve damage and nerve-fibre layer changes have been established to precede the visual
field and pressure changes in glaucoma neuropathy. These have made ocular sonography
invaluable in assessing glaucomatous eyes. Computed tomography is limited by its cost, non-
availability and the side effect of ionizing radiation. Magnetic Resonance imaging shows excellent
soft tissue resolution and is very good at imaging the optic nerve, cost and nonavailability are
however significant limitations especially in a country where majority of the populace live below
US $1.00 per day.
Ultrasound is cheap, fast, available and accessible in our environment and its sensitivity at
picking optic nerve sheath and lens changes are justification for this study. This study will also
seek to add to the existing body of knowledge on optic nerve sonography in our environment.
7
ANATOMY OF THE EYE
GROSS ANATOMY
The eye is the organ of vision and the principal component of the visual apparatus which also
includes various accessory ocular structures lodged in the orbit, the bony space in the front of the
skull17. The orbital fascia is the periosteum of the orbit which becomes continuous with the dura
mater and the optic nerve sheath at the back.
8
The eye ball is the dominant structure in the anterior orbit, embedded in fat but separated by a
membranous sac called the Tenon’s capsule18,19. The eye is divided into two segments of different
sized spheres. The smaller anterior segment which lies between the cornea and the lens and the
larger posterior segment lies between the lens and the retina (Fig.1 A and B). The anterior segment
forms 1/6th of the eyeball while the posterior segment is the larger sphere seen behind the lens and
contains the vitreous body19. The anterior segment of the eyeball is composed of two chambers
the anterior chamber which lies between the cornea and the iris, while the posterior chamber is
between the iris and the posterior lens capsule20.
The coat of the eye is composed of three layers (Fig. 2), the outermost layer is formed by the
tough white sclera posteriorly and the transparent cornea anteriorly. The junction between the
two is called the limbus20. The intermediate layer is a continuum of the vascular tissue known as
the uveal tract and is composed of choroid, ciliary body and iris. This layer may be considered as
an expansion of the arachnoid and pia of the optic nerve17. The inner layer is formed by the retina
which is a delicate nervous membrane of the eyeball.
Posteriorly the nerve fibres from the retina converge to form the optic nerve at the optic disc. The
nerve pierces both the choroid and sclera as it passes posteriorly through the optic canal and
continues as the optic nerve accompanied by the ophthalmic artery. The optic nerve, the second
cranial nerve, enters the orbit through the optic canal accompanied by the ophthalmic artery. The
nerve is really an extension of the white mater of the brain; it is covered by pia mater and lies
within a tube of arachnoid and dura mater as far as the back of the eye. The optic nerve is a
cylindrical structure between the retina and optic chiasma measuring approximately 5mm in
length and 4mm in average diameter with the sheath and 3mm in diameter without the sheath.
This can be divided into 4 main parts21:
1. Intraocular (the optic nerve head)
9
2. Intra-orbital (between globe and optic canal)
3. Intra-canalicular (within the optic canal)
4. Intracranial (between optic canal and chiasm)
The refractive media of the eye comprise of the cornea, the aqueous humour, lens and the vitreous
body. The crystalline lens lies right behind the iris (Fig.3A), it is biconvex in shape , measuring
about 9mm in diameter and 4mm in thickness18. The lens consists of three layers, the outer
capsule, inner epithelial layer and the lens nucleus. The optic axis is the line joining the anterior
pole (the central portion of the anterior curvature of the eyeball) to the posterior pole which is the
central portion of the posterior curvature. The axial length of the eye is approximately 24mm.
(A.)
10
Fig 1: Schematic diagrams of the anatomy of the eye and sonographic anatomy showing the
anterior segment structures in A, and the posterior segment structures in B. (Schematic diagram
is Courtesy; Frank H. Netter. Atlas of Human Anatomy, second edition)
) B. (
Cornea
Anterior
Chamber
Iri s
Lens
Vitreous
Chamber
Vitreous
Chamber
Optic
Nerve
11
Fig 2: Schematic diagram of the human eye, showing the optic nerve and the lens. Courtesy;
Stephanie Ryan, Michelle M, Stephen E. Anatomy for diagnostic Imaging second edition
SONOGRAPHIC ANATOMY
At the anterior pole of the eyeball, the eyelids and the conjunctiva abutting the cornea produce
a moderate echogenic structure which outlines the ventral part of the anterior chamber. With
high resolution transducers, the cornea and lens are echogenic and easily defined20. The anterior
and the vitreous chambers are anechoic spaces20(Fig 1 A and B). The pupil appears as a
translucent disruption of iris continuity. Posterior to it lies the anechoic lens with echogenic
posterior lens capsule (Fig. 3)The anterior margin of the lens is not apparent, and neither is the
posterior chamber, which is too thin to be visible. The human lens diameter is 10 mm with a
maximal thickness of 3-4 mm18. The posterior margin of the lens is convex towards the vitreous
cavity. The ciliary body produces a focal thickening of the eye wall, next to the margins of the
lens. The vitreous humour is echo free, homogeneous and occupies more than two thirds of the
12
eyeball volume. Since it only adheres to the posterior wall in a few points, movement of the
vitreous humour relative to the wall can be observed during real time scanning.
The posterior wall of the eyeball is echogenic, often with no inner layers. With high frequency
transducers and lowering of distal gain compensation, the choroid appears less echogenic than
neighbouring retina or sclera. Behind the eyeball, the intra-conal fat pad is hyperechoic19,
mainly due to acoustic enhancement in the vitreous humour. The optic nerve appears as a
sagittal hypoechoic structure, 4.5 – 5 mm thick, that runs from the outer part of the eyeball to
the tip of the orbit19 (Fig. 4). The length of the optic nerve is approximately 2.5cm. The extrinsic
muscles that form the intra-orbital muscular cone appear as hypoechoic bands with typical
longitudinal striations. The oblique muscles are almost never seen, due to their close relation to
the rectus muscles and thin belly. The rectus muscles can always be assessed, especially if
trapezoid emission of ultrasound at the surface of the transducer is used. They are oriented in a
sagittal plane and occupy the four cardinal points in the Orbit (superior, inferior, medial and
lateral).
13
14
Fig 3: Sonographic Anatomy, in B-mode, of the Lens (axial section
15
Fig. 4: Sonographic Anatomy, in B-mode, of the Optic Nerve (A) Axial section.
LITERATURE REVIEW
Glaucoma can be classified according to anterior chamber angle findings and the presence or
absence of disease causing elevated IOP and accompanying factors11. Basically, the disease can
be classified into Primary, Secondary and Developmental glaucoma. In Primary glaucoma, there
is no cause found for the elevated IOP, while in Secondary glaucoma, the elevation in IOP
results from other ocular diseases, systemic diseases, or drug use. In developmental glaucoma,
the elevation in IOP results from developmental anomalies in the anterior chamber angle
occurring during the embryonic period. Primary glaucoma is divided into primary open angle
glaucoma “broad definition” a disease concept that encompasses both conventional primary
open-angle glaucoma and normal-tension glaucoma) and primary angle-closure glaucoma11.
The primary functional and structural abnormality involved in glaucoma is glaucomatous
optic neuropathy. In recent years, the approach of including the presence or absence of
16
glaucomatous optic neuropathy in the classification of glaucoma and related diseases has
become internationally accepted.11
Primary open-angle glaucoma (POAG) is characterized by chronic progressive optic
neuropathy in which the optic disc and retinal nerve fiber layers show particular morphological
characteristics which includes thinning of the optic disc margin, retinal nerve fibre layer defects
and in which gonioscopy shows a normal anterior chamber angle. It is a disease type in which
other illnesses and congenital anomalies are absent. This is accompanied by progressive retinal
ganglion cell loss and corresponding visual field defects. Moreover, among cases of POAG,
genetic variations in myocilin or optineurin gene may be detected22.
A survey in south-eastern Nigeria, put the prevalence of glaucoma at 2.1% in people
30 years and older23. Another study in South-South Nigeria reported the prevalence of glaucoma suspects
as 2.7%24 , this correlated well with prevalence values of 2.7% in Ibadan South- West Nigeria25. A
prevalence of 1.02% was recorded amongst Hausa/Fulani ethnic extraction of North-western Nigeria26.
The suggested prevalence of glaucoma in sub Saharan Africa is 4% in people 40 years and older2 .
Risk factors for Primary Open Angle Glaucoma include increasing age, higher IOP, lower
systolic blood pressure (BP) to IOP ratio (BP/IOP), lower mean diastolic ocular perfusion
pressure (diastolic BP minus IOP), thinner central corneal thickness (CCT)27, and a positive
family history3. Racial variability of some of these risk factors at baseline has been
demonstrated; with higher IOP and thinner CCT in African-derived groups28. Age is an
important and consistent risk factor, with a higher prevalence of glaucoma associated with
increasing age1,22,24 The age-specific prevalence of POAG was higher with increasing age: From
1.7% to 5.6% in Kongwa, Tanzania, from 1.2% to 4.9% in Hlabisa, South Africa, and from
0.6% to 6.0% in Temba, South Africa in the age-group from 40-49 years to 70-79 years,
respectively1. Gender was not consistently associated with prevalent cases of glaucoma29.
However, some surveys reported a higher prevalence of POAG in men22. Men were also more
17
likely to have secondary glaucoma especially following trauma. Primary Angle Closure
Glaucoma was more common in women22
Higher IOP is another important factor associated with a higher prevalence of glaucoma
although IOP had a limited predictive value1. Hypertension was not significantly associated
with glaucoma prevalence, however, lower mean ocular perfusion pressure was associated with
a higher prevalence in the surveys in African-derived populations of Barbados and Baltimore22.
This was not reported in African-Caribbeans in London or in the only survey that this factor
was studied in Sub-Saharan Africa1. These factors associated with ocular blood flow i.e. systolic
BP, diastolic BP and ocular perfusion pressure were stronger in older people22.
A positive family history of glaucoma was associated with higher prevalence of glaucoma11,22.
The higher prevalence of glaucoma in blacks compared to whites has been consistently
demonstrated. Furthermore, those with darker skin and of African birth seemed
to have a higher risk1,22
Iris-lens channel heights <5μm would lead to pressure elevations in the posterior chamber that
would be a glaucoma risk6. This risk factor however contributed more to angle closure glaucoma
than open angle glaucoma.
Ashaye et al30 in their work which was done to determine the ocular and systemic factors
associated with neovascular glaucoma(NVG) in an African population , in a Hospital based
cross sectional study ,61 consecutively recruited patients with clinical diagnosis of NVG , had
a complete ocular evaluation. 61 subjects were studied with an identifiable aetiological factor
presumably causing neovascular glaucoma. Males outnumbered females among subjects with
NVG above 40 years, while females outnumbered males in the subjects below 40 years of age.
They therefore concluded that Medical conditions such as systemic hypertension, diabetes and
18
ocular conditions like retinal vein, retinal artery occlusion, couching and glaucoma were
associated with NVG.
A study by Quigley et al31 showed that up to 40% of the axons could be lost before a visual
field defect develops on Goldmann perimetry and that 20% of axons are lost before a 5 db loss
is detected on standard automated perimetry31. The current research efforts in the early
"preperimetric glaucoma" diagnosis are aimed either at psychological tests or alterations in the
optic nerve head morphology as assessed by scanning laser ophthalmoscope, digital image
processing of optic nerve head images or optical coherence tomography. While these advanced
technologies are relevant in glaucoma diagnosis and research, they are not practical in routine
clinical practice. It is estimated that 71% of blindness in the world is from three conditions:
cataract, trachoma, and glaucoma9. Approximately three fourths of all blind individuals reside
in Africa and Asia9. The estimates by WHO suggest that depending on geographic location,
glaucoma is responsible for 5.7 to 22.7% of all blindness worldwide. It may be fair to estimate
that around 10% of global blindness may be from glaucoma9.
Nwosu conducted a 1-year study looking for new cases of blindness at a teaching hospital
eye clinic in Anambra State, Nigeria. He found that of 257 patients with blindness, glaucoma
was responsible for 22.2% of visual impairment in at least one eye32 . In Africa, glaucoma
accounts for 15% of blindness and it is the region with the highest prevalence of blindness
relative to other regions world-wide1. Glaucoma blindness in Africa is, therefore, twice the
global figure; and eight times higher than in the Western Pacific sub-region1. However, the
numbers who are blind is just the tip of the iceberg as there are many more individuals with
glaucoma who are at the risk of blindness. Approximately 70% of glaucoma is found in
developing countries9. The commonest form of glaucoma in Nigerians is primary open angle
type found in individual ≥40 years of age33. It is estimated that two thirds of those
19
blind are cases of Primary Open Angle Glaucoma (POAG), with the majority of the remainder
being cases of angle-closure glaucoma (particularly common in China and the Far East)22.
Kyari et al1 in a study to review the epidemiology of different types of glaucoma relevant to
Sub-Saharan Africa (SSA) and to discuss the evidence regarding the risk factors for onset and
progression of glaucoma highlighted glaucoma in SSA as a public health problem with open-
angle glaucoma predominating1 They reported that glaucoma is also the second leading cause
of blindness, has a high prevalence, an early onset and progresses more rapidly than in
Caucasians1. It was learnt that these factors were further compounded by poor awareness and
low knowledge about glaucoma even by persons affected by the condition. In their conclusion
they asserted that Glaucoma care needs to be given high priority in Vision
2020 programs in Africa, and that questions remain unanswered and there is a need for further research in
glaucoma in sub-Sahara Africa. Prevalence of blindness was 4.2% (95% CI: 3.8-4.6%) in the largest study
on blindness survey done in Nigeria34 Blindness varied by age groups, sex, literacy level and geopolitical
zone. Furthermore, 84% of blindness was due to avoidable causes with cataract responsible for 43% of
blindness, glaucoma 16.7%34. There are several theories that attempt to explain the glaucomatous optic
nerve changes. The most prevalent theories attempting to explain glaucomatous optic neuropathy are the
mechanical theory and vascular theory9,14,35. In the mechanical theory emphasis is on the damage to the
optic nerve neurons at the level of the lamina cribrosa by the elevated IOP. Alternately, the raised IOP
may attenuate the sensitive microcirculation to the optic nerve head. On the other hand, the vascular theory
suggests that eyes with inherently poor vascular supply to the optic nerve head are more predisposed to
damage by elevated or normal IOP9 But the cause-and-effect relationship between nerve damage and
vascularity has not been established.
Sponsel and co-workers36 discovered that in patients with glaucoma or ocular hypertension, the
eye with the higher velocity of retinal leukocyte flow was associated with better visual function
with regard to visual fields and contrast sensitivity. It is controversial whether increased blood
velocity translates to enhanced perfusion pressure to a particular area. Further support for the
vascular theory came after the development of the laser Doppler flowmetry (LDF) technique to
evaluate the circulation of the optic nerve37. Studies have shown diminished blood flow in the
optic nerves of eyes with POAG9. As neither theory could explain all cases of glaucoma, the
trend is to combine the two views together.
20
There may be more than one mechanism of damage involved. Whatever the mechanism of
injury, there is a common result which is loss of optic nerve fibre. Genetic factors have also
been implicated in the aetiology of glaucoma38. Positive family history is a risk factor for
glaucoma. The relative risk of having POAG is increased approximately 2–4 folds for
individuals who have a sibling with glaucoma. Glaucoma, particularly POAG, is associated with
mutations in several different genes (including MYOC, ASB10, WDR36, NTF4, TBK1 genes),
although most cases of glaucoma do not involve these genetic mutations. Normal tension
glaucoma, which comprises one-third of POAG, is also associated with genetic mutations
(including OPA1 and OPTN genes).
The cup/disc (C/D) ratio of the optic nerve head enlarges with progression of glaucomatous
damage, reflecting loss of optic nerve fibres22 which are represented in the optic disc by the
neuro-retinal rim. Furthermore, investigation has shown that larger, nonglaucomatous; discs
have larger C/D ratios, and that glaucomatous optic neuropathy is more difficult to detect in
small disc. The development of glaucomatous optic neuropathy is attributed to loss of ganglion
cell axons in association with alterations in the connective tissue of the lamina cribrosa.
In POAG, which is primarily a disease of increasing age, increasing rigidity of the laminar
ECM with age has been implicated in this process. However, there is no consensus on whether
this loss of flexibility and resiliency by the lamina cribrosa is a consequence of raised lOP,
axonal loss or the ageing process alone. Increasing age is associated with axonal loss in the
retrobulbar optic nerve, but its effect on the ECM of the orbital nerve has yet to be established22.
Several researchers using different modalities have studied and documented the ocular changes
in glaucoma. The most consistent of these were the optic disc and optic nerve sheath changes
which include thinning of the optic disc margin and retinal nerve fibre layer defects. The lens is
also shown to be thickened as well as shallow anterior chamber 11. The optic nerve can be
21
imaged using methods such as A-scan ultrasonography, B-scan ultrasonography, three-
dimensional ultrasonography, computerized tomography and magnetic resonance imaging
(MRI).
However, data generated from these studies vary tremendously39. Factors contributing to this
variation are personal experience, inter-observer variability, test–retest variability, and eye
movement artefacts occurring during long acquisition times of up to several minutes in certain
MRI Protocols.
Lagre`ze et al40 in their work in normal subjects discovered that the optic nerve can be clearly
distinguished from its surrounding CSF sheath, which itself is bordered by the nerve sheath on
MRI. They showed that. MRI yielded mean optic nerve diameters of 3.23 mm at a position 5
mm behind the eye and dropped to 2.67 mm at a position 15 mm behind the eye. The same
applied to its sheath, with diameters declining from 5.72 to 3.98 mm, respectively. Compared
with MRI readings, ultrasonography consistently yielded smaller diameters. In the A-scan
mode, diameters were 2.31 mm for the retrobulbar optic nerve and 4.08 mm for the sheath.
Slightly larger diameters of the optic nerve and its sheath were obtained in the B-scan mode. In
straight gaze, the optic nerve diameters were 2.60 mm and
4.16 mm for the sheath, and in abduction they were 2.60 mm and 4.09 mm, respectively. Mean
diameters of the optic nerve and sheath obtained with all three methods (A-scan, Bscan, and
MRI) were statistically significantly different (p <0.05) and were normally distributed. In
comparisons of straight gaze and abduction, the nerve and sheath diameters obtained with B-
scan ultrasonography did not differ significantly36. ONSD was measured sonographically by
Ismail41 among Nigerian adult population , he reported a mean value of 4.11mm on the right
and 4.35mm on the left
22
Beatty and co-workers16, worked on a study designed to investigate whether measurements of
the optic nerve diameter (OND) and cross sectional area(ONCSA), as measured by B-scan
ultrasonography, are altered in glaucoma. One eye of 49 glaucoma patients and 90 control
subjects underwent five repeated echographic measurements of the maximal interpial diameter
and cross sectional area of the orbital optic nerve on two separate occasions. All measurements
were taken by one experienced ultrasonographer. The Mean ONSD for the control group was
found to be 2.86 +0.46 mm, and was independent of height, axial length, spherical equivalent,
sex, or race, but was inversely related to age. Reproducibility of OND readings in control
subjects was 0.149 mm (coefficient of repeatability). Test-retest variability of interpial diameter
was −0.02 (0.29) mm. They also found out the mean interpial diameter of the optic nerve to be
significantly smaller among glaucomatous eyes (2.58 (0.501) mm) than controls (Mann–
Whitney U test: p <0.0001). Glaucomatous optic nerves also had a significantly smaller cross
sectional area (6.68 +2.58 mm2) than those of healthy volunteers (8.25 +1.67 mm2) (p
=0.004).They finally concluded that echographic measurements of the orbital optic nerve are
highly reproducible and not subject to clinically meaningful test-retest variability. Optic nerve
interpial diameter and cross sectional area are reduced in glaucomatous eyes, reflecting nerve
fibre loss. They asserted that the technique may be useful in distinguishing between normal and
glaucomatous eyes where optic disc morphometry is inconclusive or impossible as a result of
opaque media. Beatty et al42 in another work correlated between the orbital and intraocular
portions of the optic nerve in glaucomatous and ocular hypertensive in their study. One eye of
20 volunteers (16 glaucoma subjects, 4 ocular hypertension subjects) underwent optic disc
analysis using Heidelberg retinal tomography, and echographic measurements of the retrobulbar
optic nerve. The male-to-female ratio was found to be 6.5:3.5, and the mean age of their sample
was 62.25+/-13.7 years. Orbital optic nerve diameter and cross-sectional area correlated
significantly and positively with the neuroretinal rim area (Spearman's rank correlation
23
coefficient; OND: r = 0.488,p = 0.0336; ONCSA: r = 0.619, P = 0.0079), but not with any other
topographical disc data.
The retrobulbar optic nerve cross-sectional area-to-disc area ratio (ONCSA/D) was found to have a
significant negative correlation with the cup area/disc area ratio (simple regression analysis; r = -
3.948, p = 0.046), and a statistically demonstrable positive correlation with the neuroretinal rim
area/disc area ratio (r = 0.451, p = 0.046). The results of their study indicated that orbital optic nerve
dimensions are a reflection of the neuroretinal rim area of the optic disc. Echographic measurements
of the retrobulbar nerve may be additive to the traditional triad of raised intraocular pressure, field
defects and glaucomatous optic neuropathy that suggests a diagnosis of glaucoma42.
Similar reduction in the ONSD was reported by Wang et al43 who measured the ONSD with
MRI using fat suppressed fast recovery fast spin echo T2Wi sequence. In contrast Pinto et al44
while using ultrasound found no statistically significant difference in the nerve sheath
measurements between glaucoma and normal subjects. Jaggi et al45 however demonstrated a
reduction in ONSD in glaucomatous eyes.
A study11 by the Japanese glaucoma society also showed abnormal lens findings associated
with glaucoma to include abnormal size or shape of the lens such as (lens swelling,
spherophakia) and abnormal lens position (lens luxation, lens subluxation, etc.). Abnormalities
of the ciliary zonule (congenital anomalies, trauma, exfoliative glaucoma, etc.) may play a role
in abnormal positioning of the lens11. Abnormal lens position and increased LT due to the
progression of cataracts may result in angle closure. In the case of mature or hypermature
cataracts, the complications of accompanying outflow of lens material and phacolytic glaucoma
may occur. Observation of the anterior surface of the lens is also important, and following laser
iridotomy and peripheral iridectomy, posterior synechiae may occur11. In exfoliative glaucoma,
24
deposits of white matter are observed on the anterior surface of the lens and the pupillary
margin.
In a previous study by Pinto et al46 to find out the relationship between IOP and ONSD in glaucoma,
intraocular pressure was compared with ONSD, there was a positive correlation between them in patients
with POAG (p = 0.03), borderline association with a p-value of 0.05 was however seen in patients with
normal tension glaucoma.
25
MATERIALS AND METHODS
STUDY DESIGN
The study is a prospective case control study which spanned a period of one year, from April
2015 to March 2016 in adults 30 years and above. at the Department of Radiology, Obafemi
Awolowo University Teaching Hospitals Complex, Ile-Ife, Osun State, Nigeria.
STUDY AREA
Ile-Ife is a Yoruba speaking town situated in the South Western Zone of Nigeria with a land
mass of 1902km2 and population of approximately 644,373 people excluding over 20,000
students (2006 National Population Commissions census). There are 4 local governments
namely Ife Central, Ife east, Ife north and Ife south with a total of about 50 wards (2006 Nigerian
population Commission census). The hospital is one of the tertiary referral centres serving
about 7.7 million population in the south western region of Nigeria and receiving patients from
Osun State where it is located, and adjacent neighbouring state like Ondo and Ekiti states. The
Obafemi Awolowo University Teaching Hospital Complex comprise of 3 units – located at Ile-
Ife, Ilesa and Imesi-Ile.
PATIENT SELECTION
All subjects diagnosed with glaucoma, with IOP >21mmHg and visual field showing the
glaucomatous pattern as determined by an Ophthalmologist at the Ophthalmology clinic of
OAUTHC were recruited into the study using consecutive random sampling technique
26
The control group were age and sex matched volunteers with normal IOP and optic disc with no
other ocular disease as determined by the ophthalmologist.
SAMPLE SIZE
The sample size was calculated using the Fisher’s formula; n =z2 p q/d2 Where:
n =Sample size z = Standard normal deviate =1.96 corresponding to 95%
confidence interval p = prevalence = 4%2 = 0.04 q = 1- p =0.96 d = degree of
accuracy =0.05 n = (1.96)2 x 0.04 x 0.96/ (0.05)2 n =59.007
60 study subjects with glaucoma and 60 healthy, age and sex matched control were recruited for
the study.
SELECTION CRITERIA FOR THE STUDY
The subjects group were patients diagnosed with glaucoma by an ophthalmologist.
The control group on the other hand were willing volunteers who were declared
nonglaucomatous by the ophthalmologist, with normal visual fields and normal intraocular
pressure <21mmHg. The control group were also similar in age and sex to the patients with
glaucoma.
EXCLUSION CRITERIA
• Hypertension
27
• Diabetes mellitus because it increases lens thickness
• Cataract • Ocular trauma or previous history of ocular trauma
• Smokers (because smoking also increases lens thickness )
• On-going eye infection
• Previous radiation therapy to the eye.
EQUIPMENT
The equipment will include the following
• Mindray Real time ultrasound Machine , Model DC-7 ,with 6.5-12MHz linear probe
• Coupling gel
• Blood pressure measuring apparatus
• Goldmann’s Applanation Tonometer, Ophthalmoscope, Pen torch, Gonio lens, Perimeter, Slit
Lamp biomicroscope
• Disposable gloves and wipes
• Weighing scale and a stadiometer for weight and height determination respectively..
TECHNIQUE
A clearly written consent form (Appendix 1) was administered to each subject to sign, upon
understanding and agreeing to the procedure. Each subject had their blood pressure taken and
the values were noted. Those with values >140mmHg and 90mmHg for systolic and diastolic
blood pressure respectively were excluded from the study. Those with fasting blood glucose in
excess of 5.5mmol/l were also excluded from the study. The referring ophthalmologist recruited
patients who met the inclusion criteria. Information such as duration of illness, subject age and
28
history of hypertension and smoking were obtained from each subject. The height and weight
of each subject was taken using a stadiometer and a weighing scale respectively. Their body
mass index (BMI) was calculated using the formula: Weight (Kg) /
Height (m2).
All subjects for the study were examined between 12 noon and 4pm, to eliminate the effects of
circadian rhythm on intraocular pressure. After thorough explanation of the procedure, each
patient was examined in the supine position. Trans-orbital scan of each eye was performed using
a 6.5 – 12MHZlinear probe. Subjects’ eyes were closed and copious acoustic gel was applied
to the closed upper lid. The transducer was then placed on the coupling gel on the temporal
region of the eye lid. Minimal pressure was applied during the examination to avoid any
discomfort to the patient as well as minimizing pressure to the globe. The probe was then moved
from the supero-temporal region toward the region of the optic nerve entry. Proper probe
angling was employed to see the optic nerve in its axial plane. To achieve this, patient was asked
to direct his or her gaze in primary position with the probe marker centred on the cornea.
Transverse (cross-section) and longitudinal scans of both optic nerves were obtained for
assessment of nerve sheath diameter. The transverse scan was done by placing the probe on the
globe with the marker parallel to the limbus in two directions either nasally or superiorly. The
longitudinal scan was performed by placing the probe peripheral to the limbus with the probe
marker perpendicular to the limbus.
The ONSD was measured by placing the cursor on the outer contours of the dural sheath in the
retrobulbal position at a distance 3mm behind the posterior wall of the eyeball A→B (Fig.5).
The ONSD was measured as the horizontal distance between the cursors. Bilateral ONSD was
measured three consecutive times and the mean value was documented.
29
Axial lens thickness was measured by placing the cursors on the outer part of the anterior and
posterior lens capsules A→B in (Fig.6). LT in both eyes was obtained 3 consecutive times and
documented. The mean value for each eye was obtained.
Fig. 5 B-mode sonographic measurement of the Optic Nerve (axial plane), seen as the
anechoic structure between cursors (A→B).
30
DATA AND STATISTICAL ANALYSIS Data was entered into a computer and analysed using Statistical Package for Social Sciences
(SPSS) for windows (SPSS INC. USA) version 18.0. Categorical variables such as
sociodemographic characteristics of respondents were presented on contingency tables for both
groups, and these variables were compared between the glaucomatous and control groups using
chi-square test. Continuous variables like LT and ONSD were presented by their means and
standard deviations (mean ± SD) for both glaucomatous and control groups. LT and ONSD in
both groups were compared statistically using independent sample t-test. Correlation and
regression analysis were used to evaluate the relationship between age, LT and ONSD in the
A
Fig 6 : B - s mode onographic m the of easurement LT ( axial plane) , ( A→B) seen as anechoic space the
between the echogenic capsules between the cursors.
31
glaucomatous group while controlling for other variables.. The level of statistical significance
was determined at p values less than 0.05 and the results were presented in frequency
distribution tables, charts and graphs.
ETHICAL CONSIDERATIONS
The Approval for this study (Appendix 11) was sought and obtained from the Ethical and
Research committee of the Obafemi Awolowo University Teaching Hospital Complex IleIfe, Osun
state, South-Western Nigeria.
32
RESULTS
Table I. Patients' General Characteristics
P
Variables Glaucoma Controls χ2 df value
(n = 60) (n = 60)
Age (years)
30 – 39 7 (11.7) 13 (21.7)
40 – 49
50 – 59
16 (26.7)
11 (18.3)
15 (25.0)
12 (20.0) 2.951 4 0.566
60 – 69 19 (31.7) 16 (26.7)
≥ 70 7 (11.7) 4 (6.7)
Mean ± SD 55.5 ± 11.9 52.1 ± 11.9 1.561 118 0.121*
(Min - Max)
Gender
33.0 - 79.0 31.0 - 78.0
Male 32 (53.3) 27 (45.0) 0.834 1 0.361
Female 28 (46.7) 33 (55.0)
Weight (Mean ± SD) (Kg) 64.8 ± 11.2 70.3 ± 16.0 -2.320 118 0.033*
Height (Mean ± SD) (m) 1.65 ± 0.10 1.63 ± 0.08 0.717 118 0.475*
BMI (Mean ± SD) (Kg/m2)
BMI categories
24.10 ± 4.83 26.21 ± 5.14 -2.320 118 0.022*
Underweight 6 (10.0) 4 (6.7)
Normal 33 (55.0) 25 (41.7) 3.673 3 0.299
Overweight 13 (21.7) 17 (28.3)
Patient category, n (%)
33
Obese
Duration of glaucoma (Mean ± SD)
8 (13.3) 14 (23.3)
(months) 1.2 ± 0.4 NA
χ2 - Chi square; df - degree of freedom; * independent samples t test; SD - Standard deviation
Table 1 summarises the age, sex and other characteristics of the participants of this study. In this
prospective case control study, a total of 120 subjects between the ages of 30 and 80 years were
included. They comprised 60 glaucoma subjects and 60 controls. Thirty-two (53.3%) of the
glaucomatous subjects were males and 28 (46.7%) were females while there were 27(45%) males
and 33(55%) females in the control subjects. This difference in their gender composition was
however not statistically significant (x2=0.834, df=1, p=0.361). The mean age of the glaucoma
subjects was 55±11.9 years while that of the control was 52.1±11.9 years (t = 1.561, df = 118, p =
0.121.). Participants in both study groups were also statistically similar in other general
characteristics except for their weight and BMI. The mean weight and BMI for the control subjects
were greater than those for glaucoma subjects, these values were statistically significant with p
values of 0.033 and 0.022 for weight and BMI respectively. However more than half of the subjects
investigated had normal weight with only a few being underweight, overweight and obese (x2 =
3.673, df = 3, p = 0.299) (Table 1). Of the 60 glaucomatous subjects, 54(90.0%) had POAG,
5(8.3%) had normal tension glaucoma and 1(1.7%) had angle closure glaucoma (Fig.7).
34
Fig. 7: Bar chart showing distribution of different types of glaucoma Table II. Differences in IOP, ONSD
and LT between the study groups
Patient category
Variables Glaucoma Controls t df P value
(n = 60) (n = 60)
Right IOP (mmHg) 17.3 ± 8.1 14.5 ± 3.1 2.560 118 0.012
Left IOP (mmHg) 17.1 ± 7.6 15.0 ± 3.3 2.034 118 0.045
(90.0 % 54 )
1 (1.7 % )
5 (8.3 % )
0
10
20
30
40
50
60
POAG Normal tension Glaucoma ACG
Type of Glaucoma
35
Right ONSD (mm) 3.57 ± 0.19 4.23 ± 0.34 -12.881 118 < 0.001
Left ONSD (mm) 3.59 ± 0.33 4.26 ± 0.30 -11.441 118 < 0.001
Right lens thickness (mm) 4.15 ± 0.43 4.01 ± 0.56 1.615 118 0.109
Left lens thickness (mm) 4.18 ± 0.46 3.99 ± 0.45 2.285 118 0.024
COMPARISON BETWEEN ONSD AND LT AMONG BOTH GROUPS
Table II shows the difference in, ONSD and LT between the glaucoma and control groups. The
mean ONSD in glaucoma patients was 3.57 ± 0.19 mm on the right and 3.59 ± 0.33mm on the
left. The mean ONSD among controls were 4.23 ± 0.34 mm and 4.26 ± 0.30mm on the right
and left respectively. The right ONSD of the glaucomatous patients had a lower mean of
3.57 ± 0.19 mm compared to that of the controls of mean of 4.23 ± 0.34 mm. Their left mean
ONSD was also lower (3.59 ± 0.33mm) than that of the controls (4.26 ± 0.30mm) (Table II).
36
These are also highlighted in figures 8 and 9 which showed statistically significant differences
between both groups (p = 0.000).
Right LT of the glaucomatous patients had a mean of 4.15 ± 0.43mm while the controls had a
mean of 4.01 ± 0.56mm (p = 0.109) (fig. 10). The mean left LT of the glaucomatous patients
was however higher at 4.18 ± 0.46mm compared to that of the controls at 3.99 ± 0.45mm (fig
11). In addition the mean intraocular pressure of both eyes of glaucoma subjects was
significantly higher than the mean for controls as shown on Table II.
37
Fig 8: Boxplot showing the pattern of Right ONSD among glaucomatous patients
(p = 0.000)
38
Fig 9: Boxplot showing the pattern of Left ONSD among glaucomatous
patients (p = 0.000)
39
Fig. 10: Boxplot showing pattern of right lens thickness among study
participants (p = 0.109)
40
Fig. 11: Boxplot showing pattern of left lens thickness among
glaucoma patients (p = 0.024)
.
41
Table III. Paired comparison of IOP, ONSD and Lens thickness among study subjects
Mean ± SD
Variables t* P value
Right Left
IOP (mmHg)
Glaucoma 17.3 ± 8.1 17.1 ± 7.6 0.218 0.828
Controls
ONSD (mm)
14.5 ± 3.1 15.0 ± 3.3 -2.259 0.028
Glaucoma 3.57 ± 0.19 3.59 ± 0.33 -0.513 0.610
Controls
Lens thickness (mm)
4.23 ± 0.34 4.26 ± 0.30 -1.413 0.163
Glaucoma 4.15 ± 0.43 4.18 ± 0.46 -0.967 0.338
Controls 4.01 ± 0.56 3.99 ± 0.45 0.341 0.734
* Paired-samples t test
42
As highlighted by a paired comparison of right and left eyes on Table III, there were no
statistically significant differences in both ONSD and LT of glaucoma subjects and controls.
The mean ONSD values were 3.57 ± 0.19mm and 3.59 ± 0.33mm for glaucomatous eyes on the
right and left (p = 0.610) while the control subjects had mean values of 4.23 ± 0.34mm and 4.26
± 0.3mm (p = 0.163) on the right and left respectively. Similarly, the mean LT were 4.15 ±
0.43mm and 4.18 ± 0.46mm for glaucomatous eyes on the right and left (p = 0.338) while the
control subjects had mean values of 4.01 ± 0.56mm and 3.99 ± 0.45mm (p = 0.734) on the right
and left respectively(Table III).
Table IV. Correlation between respondents' Age, ONSD and Lens thickness
43
Correlation –
Age vs. :
Glaucoma Controls
R P value r P value
Right ONSD -0.230 0.077 -0.549 0.000
Left ONSD -0.191 0.144 -0.548 0.000
Right lens thickness 0.456 0.000 0.068 0.603
Left lens thickness 0.408 0.001 -0.032 0.811
r - Pearson correlation coefficient,
44
RELATIONSHIP BETWEEN AGE, ONSD AND LENS THICKNESS
A weak and negative correlation was observed between the age and ONSD of glaucoma
patients in both eyes with Pearson correlation coefficients of -0.230 (p = 0.077) and -0.119
(p = 0.144) on the right and left respectively, while a strong and statistically significant
negative correlation was observed in the control subjects (p = 0.000) on either sides (Table
IV).
The LT strongly correlated with the age of the glaucoma patients on the right(r = 0.456, p =
0.000) and left (r = 0.408, p = 0.001) respectively. No significant correlation was observed
between the LT and age of control subjects on the right and left sides (Table IV).
45
Table V. Simple linear Regression analyses for predictors of lens thickness in Glaucoma patients
Model Dependent
variables
Independent
variables
B SE t P value R2
1
Right lens
thickness (RLT)
(mm)
(Constant) 3.235 0.208
2
Left lens
thickness (LLT)
(mm)
Age (years) 0.017 0.004 3.906 0.000
(Constant)
Age (years)
3.314
0.016
0.005
3.402
0.001
0.166
Regression equations
Mode1: RLT (mm) = 3.235 + 0.017*Age (years)
Mode2: LLT (mm) = 3.314 + 0.016*Age (years)
B - regression coefficients; SE - standard error; R2 - Model variance
46
As highlighted on Table V, bivariate analysis in glaucomatous patients showed weak but
significant positive correlation between right and left LT with age, and a weak negative
correlation with height for the left LT only (r = 0.456, p =0.000; r = 0.408, p = 0.001; r = 0.301,
p = 0.019 respectively). Consequently, linear regression analyses were performed to ascertain
the influence of age alone (Models 1 and 2) on the right and left LT as shown on
Table V. Age of the patients significantly predicted the respective lens thickness values in the
Models. In Model 1, Age was responsible for only 20.8% (Model variance, R2 = 0.208) of the
variation observed in right LT compared to 16.6% in Model 2 for the left LT.
47
Table VI. Discordant / Regular pattern of the IOP and ONSD
Variables Glaucoma Controls χ2 Df P value
(n = 60) (n = 60)
Discordant 40 (66.7) 29 (48.3)
4.126 1 0.042
Regular pattern 20 (33.3) 31 (51.7)
RELATIONSHIP BETWEEN IOP AND ONSD
Patient category, n (%)
48
Although no statistically significant difference was observed between the mean IOP values of
the right and left eyes of glaucomatous patients, the mean values of 14.1±0.31mm and
15.0±3.3mm on the right and left respectively among the controls showed a statistically
significant difference(t = -2.259, p = 0.028) as shown on Table III. A comparison of IOP with
ONSD showed a predominant discordant pattern of relationship among glaucomatous patients
(discordant meaning an increase IOP was associated with an increase in ONSD) accounting for
66.7% of all cases, meanwhile only about a third of glaucoma patients showed the regular
pattern (regular meaning an increase in IOP was related to a decreasing ONSD) (χ2 = 4.126, df
= 1; p = 0.042). Among the controls there was just a marginal increase of the regular pattern
over the discordant pattern as shown on Table VI.
DISCUSSION
49
Glaucoma has consistently ranked the second leading cause of blindness10-12 and the leading
cause of preventable and rather unfortunately, irreversible blindness globally11,13. The definition
of this disease continues to evolve, allowing for continual modification of detection methods,
treatment end-points and therapeutic options14. Glaucoma is traditionally assessed by the triad
of tonometry, visual field testing and optic nerve evaluation15,16. Several ocular and sometimes
non-ocular factors can however impair the usefulness of these morphological and functional
assessment variables in the evaluation of glaucoma suspects15. These factors include but are not
limited to an opaque media i.e. cataract, mental and sometimes physical limitations of patients15.
There arises a need therefore to look away from this traditional triad of assessment to a more
objective way of evaluating glaucoma, independently of IOP and optic nerve head morphology.
This present study set out to evaluate the ONSD with the aid of ultrasound. It was a prospective
study carried out among Nigerian adults between the ages of 30 and 80 years. There was a male
gender preponderance, a finding which was similar to other studies done in the past8,47,48.
However a study conducted by Kosoko-Lasaki et al49 reported that this finding was
inconsistent, this was corroborated by a study done in Ghana by Ntim-Amponsah et al50. POAG
was the predominant type observed in the present study accounting for 90% of all
cases, this also is consistent with the findings in previous works on glaucoma1,5,12. In fact
Yilchung et al13 reported that POAG has the highest prevalence in Africa and that male gender
and urban dwellers are more likely to have POAG compared to the female gender and rural
dwellers, the reason for this finding is unclear. It has also been documented that males are more
likely to have secondary glaucoma following trauma51 , this could not be established in this
study because ocular trauma was an exclusion criterion. The mean age of glaucoma subjects is
55.5 ± 11.9 years which is also comparable to the mean age in a previous studies8,52 that
documented mean age of 56years52. The highest number of glaucoma subjects was found among
the 60-69 years age group, which is in support of earlier documented age specific prevalence
50
of glaucoma1. The reason for this could be that advancing age is a risk factor for developing
glaucoma1,53.
The study also set out to see the relationship between the intraocular pressure and the size of the
optic nerve sheath. This study shows a statistically significant difference between the mean
ONSD of glaucoma group and control subjects. The measured mean ONSD in normal healthy
controls is comparable with results obtained from previous studies41 . The study reported a mean
ONSD of 4.18mm (SD 0.49) and 4.17mm (SD 0.44) on the right and left respectively. The mean
ONSD in glaucoma patients was statistical significantly reduced compared with the mean found
in normal healthy controls. This reduction in optic nerve diameter observed in this study in
glaucoma is comparable with those of previous
studies15,16,39,43 on ultrasound and MRI. Wang et al43 used MRI to study the eyes of glaucoma
patients, they measured the ONSD at 3mm, 9mm and 15mm behind the eye ball. At 3mm behind
the eye ball, ONSD of Normal tension glaucoma (NTG) group is significantly narrower than
control group (p<0.05). At 9mm, the ONSD of the NTG group and POAG group are both
significantly narrower than the control group (p<0.05). At 15mm, the ONSD of the NTG group
and POAG group are both significantly narrower than the control group (p<0.05). Contrary to
the reduction in ONSD reported in the present study Pinto et al44 reported no difference between
the measured ONSD of glaucoma patients and healthy controls. Jaggi et al45 however showed
an increase in the ONSD of glaucoma patients. These discrepancies in the ONSD values may
reflect differences in patient selection criteria such as age, head position, sample size and most
importantly imaging modality. While ultrasound was used in this study, Jaggi used computed
tomography and their sample size was only 18 subjects.
This study revealed an inverse, though weak, negative correlation between age and ONSD
among glaucoma patients as well as in control, indicating that the reduction in the ONSD could
not have been due to the disease process alone, but age may also play a part in the atrophy of
51
the optic nerve. This was also documented in previous study by Beatty et al15. This finding is
also consistent with histological studies, reporting an age related decrease in axonal count of
the human optic nerve15. This could also be due to older individuals having a more vulnerable
optic nerve or have suffered more frequent and prolonged insult to the nerve over their life time,
both mechanisms could also play a role in concert to cause atrophy of the optic nerve3. The
weak correlation in this study is contrary to what was observed by the aforementioned
researcher who recorded a strong correlation, the difference is possibly due to the different
geographical area where both studies were carried out and may also depend on the racial factors
as the present study was conducted among dark skinned Africans as opposed to the Caucasian
population in their study.
The mean LT was not statistically different in the glaucoma and control groups on the right, but
a statistically significant difference was observed on the left in this study with a p-value of
0.024. The reason for this unilateral difference cannot be established in this study. From
comprehensive literature search, it has been observed that the lens is thickened in closed angle
glaucoma11 when compared with controls but this has not been documented in other forms of
glaucoma. Furthermore this study has also shown a positive correlation between LT and age
among glaucoma patients with a p-value of 0.000 and 0.001 in the right and left eyes
respectively. A weak negative correlation was also noted on the left in controls, but no
correlation was observed on the right. By the forgoing, it may be possible to predict the lens
thickness using the age of patients with glaucoma and vis-versa. Age is however a weak
predictor of LT in controls. Hence by linear regression analysis it was demonstrated that age is
a significant predictor of lens thickness.
The glaucomatous optic neuropathy has been widely diagnosed; this optic nerve atrophy which
is due to loss of retinal fibre layer (RNFL) has also been demonstrated in glaucomatous eyes. It
is therefore not surprising to have observed this reduction in the optic nerve sheath diameter in
52
this study among glaucoma patients compared with healthy normal subjects. The result of this
study should assist the clinician in further evaluation of glaucoma patients and also assist in
screening of glaucoma suspects, especially in the setting of an opaque media where examination
of the fundus might prove difficult or impossible.
LIMITATIONS
Ultrasound being user dependent, may give rise to minor but negligible variation in values
obtained. Moreover all measurements were done by the same researcher; hence inter-observer
53
reliability was not evaluated. Most researchers used ultrasound machines with probe frequency
of 20MHz, this study however utilized a 6.5-12MHz machine, and the effect of this was
expected to be negligible as frequencies beyond 10MHz have shown equally reliable results.
54
CONCLUSION
Real time B-mode ultrasound scan has been shown by this study to be a useful tool in
determining the ONSD as well as LT in normal and glaucomatous subjects. It also demonstrated
the reduction of the ONSD in glaucomatous eyes. Hence it can be an alternative tool in the
assessment of eyes of patients with glaucoma as well as screening for glaucoma suspects where
the traditional triad of tonometry, visual field testing and optic nerve evaluation are impossible
or not available.
55
RECOMMENDATION
In resource poor regions like ours, B-mode ultrasound could be recommended as the initial
screening method for glaucoma suspects. Further studies to ascertain possible reason for the
differences in our result of ONSD values against those reported in previous literatures is also
recommended.
56
REFERENCES
1. Kyari F, Abdull MM, Bastawrous A, Gilbert CE, Faal H. Epidemiology of glaucoma in sub-
saharan Africa: prevalence, incidence and risk factors. Middle East Afr J Ophthalmol .
2013;20(2):111-125
2. Cook C. Glaucoma in Africa: size of the problem and possible solutions. J Glaucoma.
2009;18(2):124-128.
3. Omoti A, Edema O. A review of the risk factors in primary open angle glaucoma. Niger J Clin
Pract. 2007;10(1):79-82.
4. Adio AO, Onua AA. Economic burden of glaucoma in Rivers State, Nigeria. Clin Ophthalmol
(Auckland, NZ). 2011;6:2023-2031.
5. Stone EM, Fingert JH, Alward WL, Nguyen TD, Polansky JR, SundenetSLF et al.
Identification of a gene that causes primary open angle glaucoma. Science.
1997;275(5300):668-670.
6. Silver D, Quigley H. Iris Structure, Aqueous Flow, and Glaucoma Risk. Johns Hopkins APL
Tech Dig. 2010;28(3):224-225
7. Zeng Y, Liu Y, Liu X, Chen C, Xia Y, Lu M et al. Comparison of lens thickness
measurements using the anterior segment optical coherence tomography and A-scan
ultrasonography. Invest Ophthalmol Vis Sci. 2009;50(1):290-294.
8. Nosiri C, ChawaT S, Gambo A. Prevalence of Glaucoma In Nigeria. Internet Journal of
Epidemiology. 2010;9(1).1-5
9. Zimmerman TJ, Kooner KS. Clinical pathways in glaucoma: Thieme; 2001.chapter2. 23-38
10. Oluleye TS. Causes of blindness in South -Western Nigeria. Eur J Ophthalmol.2006
16(4):604-7.
11. Haruki Abe YK, Yasuaki Kuwayama, Morohiro Shirajashi,Shiroaki Shirato, Hidenobu
Tanihara, Goji Tomita, et al. Guidelines for glaucoma. The Japan glaucoma society 2006:13-
31.
57
12. Abdu L. Epidemiological Properties of Primary Open Angle Glaucoma in Nigeria. J
Ophthalmol. 2013;(2013)1-6
13. Tham Y-C, Li X, Wong TY, Quigley HA, Aung T, Cheng C-Y. Global Prevalence of
Glaucoma and Projections of Glaucoma Burden through 2040: A Systematic Review and
Meta-Analysis. Ophthalmol. 2014;(121) 2081-2090
14. Cohen SL. New advances in the management of glaucoma. Clin refract optom. 2004;15(4)116-
126
15. Beatty S, Good P, McLaughlin J, O’Neill E. Echographic measurements of the retrobulbar
optic nerve in normal and glaucomatous eyes. British journal of ophthalmology.
1998;82(1):43-47.
16. Beatty S, Good P, McLaughlin J, O'Neill E. Correlation between the orbital and intraocular
portions of the optic nerve in glaucomatous and ocular hypertensive eyes. Eye(Lon).
1998;12(4):707-713
17. Last R, McMinn R. Last's anatomy, regional and applied: Churchill Livingstone (Edinburgh
and New York); 1994.(9) : 505-513
18. Sutton D. Textbook of radiology and imaging seventh ed: London: Churchill Livingstone,
2003; 2 .1551-1554
19. Bhargava SK. Step by Step Ultrasound: JP Medical Ltd; 2010; 149-153
20. Ryan S, McNicholas M, Eustace SJ. Anatomy for diagnostic imaging: Elsevier Health
Sciences; 2011. 23-28
21. Marjanovic I. The Optic Nerve in Glaucoma. The mystery of glaucoma: InTech2011.
22. Gayati ahuja OPA. A book of the Glaucomas. Chapter4 21-30
23. Ekwerekwu CM, Umeh R. The prevalence of glaucoma in an onchoendemic community in
South-Eastern Nigeria. West Afr J Med. 2002;21(3):200-203.
24. Pedro-Egbe C, Waziri-Erameh J. Prevalence of glaucoma suspects and pattern of intra-ocular
pressure (IOP) distribution in Ahoada-East local government area of Rivers State. Port
Harcourt. Med J 2009;4:17-22.
25. Agbeja-Baiyeroju A.M, Bangboye E, Omokhodion F, and.Oluleye T.S. The Ibadan Gluacoma
Study. Afr J Med Med Sci 2003;32(4):371-376.
58
26. Murdoch IE , Cousens SN , Babalola OE , Yang YF , Abiose A , Jones BR. Glaucoma
prevalence may not be uniformly high in all black populations. Afr J Med Med Sci.
2001;30(4):337-339
27. Abegão Pinto L, Vandewalle E, Stalmans I Disturbed correlation between arterial resistance
and pulsatility in glaucoma patients. Acta Ophthalmol 2012: 90: e214–220.
28. Sample PA, Girkin CA, Zangwill LM, Jain S, Racette L, Becerra LM et al. The African
descent and glaucoma evaluation study (ADAGES): Design and baseline data. Arch
Ophthalmol. 2009;127(9):1136-1145.
29. Omofolasade Kosoko-Lasaki GG, Gleb Haynatzki, M. Roy Wilson. Race, Ethnicity and
Prevalence of Primary Open-Angle Glaucoma. J Natl Med Assoc
2006;96(10):1624-1629.
30. Ashaye A, Adeoti C. Neovascular glaucoma in a Nigerian African population. East Afr Med
J.. 2007;83(10):559-564.
31. Quigley H, Dunkelberger G.R, Green W.R. Retinal cell atrophy correlated with automated
perimetry in human eyes with glaucoma. Am J Ophthalmol. 1989;107:453464.
32. S.N N. Blindness and visual impairment in Anambra Nigeria. trop geogr Med J. 1994;46:346-
349.
33. Oladigbolu K, Abah E, Chinda D, Anyebe E. Pattern of eye diseases in a university health
service clinic in northern Nigeria. Niger J Med. 2012;3(4):334-7.
34. Rabiu M M, Kyari F, Ezelum C, Elhassan E, Sanda S, Murthy GVS et al. Review of the
publications of the Nigeria national blindness survey: methodology, prevalence, causes of
blindness and visual impairment and outcome of cataract surgery. Ann Afr Med
2012;11(3):125.
35. Arnold AC. Normal tension glaucoma and aion: comparisons and contrasts. 111-120.
36. Sponsel W, DePaul K, Kaufman P. Correlation of visual function and retinal leukocyte
velocity in glaucoma. Am J Ophthalmol. 1990;109(1):49-54.
37. Riva CE, Harino S, Petrig B, Shonat R. Laser Doppler flowmetry in the optic nerve. Exp Eye
Res. 1992;55(3):499-506.
38 Wikipedia.Glaucoma.2014;
http://en.wikipedia.org/w/index.php?title=Glaucoma&%20oldid=592838192
59
39. Lagrèze WA, Gaggl M, Weigel M, Schulte-Monting J, Buhler A, Bach M et al.
Retrobulbar optic nerve diameter measured by high-speed magnetic resonance imaging
as a biomarker for axonal loss in glaucomatous optic atrophy. Invest Ophthalmol Vis
Sci 2009;50(9):4223-4228.
40. Lagrèze WA, Lazzaro A, Weigel M, Hansen H-C, Hennig J, Bley TA et al.
Morphometry of the retrobulbar human optic nerve: comparison between conventional
sonography and ultrafast magnetic resonance sequences. Invest Ophthalmol Vis Sci.
2007;48(5):1913-1917.
41. Ismail A. Transorbital Sonographic Measurement of Normal Optic Sheath Nerve
Diameter in Nigerian Adult Population. Malays J Med Sci MJMS. 2014;21(5):24-29.
42. Beatty S, Good PA, McLaughlin J, O'Neill E C, Correlation between the orbital and
intraocular portions of the optic nerve in glaucomatous and ocular hypertensive eyes.
Eye . 1998; 12:707–713.
43. Wang N, Xie X, Yang D, Ren R, Xian J, Li Y et al. Evaluation of Optic Nerve And
Optic Nerve Sheath Diameter In Primary Open Angle Glaucoma With 3-Tesla Magnetic
Resonance Imaging. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3963.
44. Pinto LA, Vandewalle E, Pronk A, Stalmans I. Intraocular pressure correlates with optic
nerve sheath diameter in patients with normal tension glaucoma. Graefe's Arch Clin Exp
Ophthalmol 2012;250(7):1075-1080.
45. Jaggi GP, Miller NR, Flammer J, Weinreb RN, Remonda L, Killer HE. Optic nerve
sheath diameter in normal-tension glaucoma patients. Br J Ophthalmol. 2012;96(1):53-
56.
46. Pinto LA, Vandewalle E, Pronk A, Stalmans I. Intraocular pressure correlates with optic
nerve sheath diameter in patients with normal tension glaucoma. Graefe's Arch Clin Exp
Ophthalmol 2012;250(7):1075-1080.
47. Nosiri C, Chawat S, Abba G. Prevalence of Glaucoma in Nigeria. The Int J Epidemiol.
2011;9(1). 1-5
48. Abdull MM, Gilbert CC, Evans J. Primary open angle glaucoma in northern Nigeria:
stage at presentation and acceptance of treatment. BMC Ophthalmol. 2015;15(1):1
49. Kosoko-Lasaki O, Gong G, Haynatzki G, Wilson MR. Race, ethnicity and prevalence
of primary open-angle glaucoma. J Natl Med Assoc2006;98(10):1626-1629
60
50. Ntim-Amponsah C, Amoaku W, Ofosu-Amaah S, Ewusi SR, Idirisuriya-Khair
R, Nyatepe-Coo E et al. Prevalence of glaucoma in an African population. Eye.
2004;18(5):491-497.
51. Rotchford AP, Kirwan JF, Muller MA, Johnson GJ, Roux P. Temba glaucoma study:
a population-based cross-sectional survey in urban South Africa. Ophthalmol 2003;110(2):376-
382.
52. Gyasi M, Amoako W, Adjuik M. Presentation patterns of Primary open angle glaucomas
in North Eastern ghana. Ghana Med J. 2010;44(1). 25-30
53. Kyari F, Gudlavalleti MV, Sivsubramaniam S, Selvaraj Sivsubramaniam; Clare E.
Gilbert; Mohammed M. Abdul et al. Prevalence of blindness and visual impairment in
Nigeria: The national blindness and visual impairment survey. Invest Ophthalmol Vis
Sci. 2009;50(5):2033-2039.
APPENDIX I
OBAFEMI AWOLOWO UNIVERSITY TEACHING HOSPITALS COMPLEX, ILE-IFE.
SONOGRAPHIC DETERMINATION OF OPTIC NERVE SHEATH DIAMETER IN
GLAUCOMA IN NIGERIAN ADULTS AT THE OBAFEMI AWOLOWO
UNIVERSITY TEACHING HOSPITAL COMPLEX ILE-IFE.
SUBJECT INFORMATION SHEET
Principal Investigator: Omatiga Achimugu Gabriel Telephone No:- 08068885667
Institution: ObafemiAwolowo University Teaching Hospitals Complex, Ile-Ife
Title of Study.SONOGRAPHIC DETERMINATION OF OPTIC NERVE SHEATH
DIAMETER IN GLAUCOMA IN NIGERIAN ADULTS AT THE OBAFEMI
AWOLOWO UNIVERSITY TEACHING HOSPITAL COMPLEX ILE-IFE.
Co – Investigators: None
Sponsor (If any): Nil
61
Some general things to know about the study: From a random selection process you have been
chosen as one of the participants in a research study. This document is designed to provide you
with the necessary information about this study and obtain your consent to participate.
What is the purpose of this study: This is to determine the usefulness of ultrasound scanning
in determining your optic nerve sheath diameter and lens thickness, as a glaucoma patient,
and to see if your age has any effect on your lens thickness, which can help to predict chances
of you becoming blind from glaucoma and advice you on early institution of appropriate
therapy.
Procedures: You will be interviewed and questions will be asked about your demographic characteristics
and medical history. I will ask you a number of questions to solicit this information and the entire
interview should last no longer than two minutes. Then you will be sent to Ophthalmology department to
check if you are having glaucoma. You will be required to come fasting and I will obtain a drop of 0.1ml
of blood from you to check your fasting blood sugar level, and then do an ultrasound scan of your eyes.
The ONSD and the LT will be measured with your eyes closed, and then the values will be documented.
Benefits: If you agree to take part in this study, you will be able to know if your glaucoma has
affected your optic nerve sheath diameter and thickness of the lenses and to what degree, which
might cause you to develop blindness. This will help your doctors to give you appropriate early
treatment so that you will not have visual impairment from glaucoma. By participating in this
study, you will also be helping in adding to and improving on the existing medical knowledge
and care of individuals with glaucoma. Costs of Participation: There is no financial cost to
participation
Risks: Needle prick to obtain blood from you for blood glucose assessment (control group) will
cause some pain. There could also be minimal discomfort from the applied gel and slight
pressure on your eyes when probe is applied
Compensation: There will be no compensation for participating in the study.
62
Confidentiality: All information gathered in this study will be kept confidential. When findings
of this study are reported in scientific journals or meetings, you will not be identified. All
records and any other study materials will be protected with password and/or stored in the
locked cabinets which will be accessible to only authorized personnel.
Respondents’ Rights: you have a right to decline participation in the study and can also withdraw from
the study at any time.
Conflict of Interest: To the best of my knowledge, there is none.
For the Records: You will be given a copy of this form to keep.
OBAFEMI AWOLOWO UNIVERSITY TEACHING HOSPITALS COMPLEX, ILE-IFE.
SONOGRAPHIC DETERMINATION OF OPTIC NERVE SHEATH DIAMETER IN
GLAUCOMA IN NIGERIAN ADULTS AT THE OBAFEMI AWOLOWO UNIVERSITY TEACHING
HOSPITAL COMPLEX ILE-IFE.
Subject’s Agreement/Consent Form:
I have read the information provided in the Subject Information Sheet, or it has been read to me. I have had the opportunity to ask questions about the research and any questions I have asked have been answered to my satisfaction. I consent voluntarily to participate in this study and understand that a drop of blood will be taken from me and my eye will be screened. I have the right to withdraw from the study at any time. I have agreed to participate in the study.
Yes No
------------------------------------------------------------------------------------------------------
Signature/Thumb print of Research Respondent. Date:
Printed Name of Research Subject’s Legal Guardian.
Signature/thumb print of Person Obtaining Consent.
Date:
63
Printed Name of Person Obtaining Consent.
APPENDIXII
APPENDIXIII
64
QUESTIONNAIRE
DEMOGRAPHIC DATA
(1) DATE (4) SEX
(2) INITIALS. (5) HOSPITAL NO
(3) AGE (6) PHONE NO
MEDICAL HISTORY:
(7) HISTORY OF HYPERTENSION YES /NO
(8) HISTORY OF TRAUMA TO THE EYE YES / NO
(9) PREVIOUS EYE SURGERY YES / NO
(10) PREVIOUS RADIATION THERAPY TO THE EYE YES / NO
(11) ONGOING EYE INFECTION YES / NO
(12) HISTORY OF SMOKING YES / NO
(13) CHRONIC USE OF STEROIDS YES / NO
STUDY DATA
(14) INTRAOCULAR PRESSURE. RT. EYE; LT. EYE;
(15) CUP DISC RATIO RT.EYE; LT.EYE.
(16) WEIGHT
(17) HEIGHT
(18) BLOOD SUGAR
(19) BLOOD PRESSURE
OPTIC NERVE SHEATH DIAMETER (ONSD) ON ULTRASOUND
RIGHT EYE LEFT EYE
1 1
2 2
3 3
65
MEAN ONSD…………mm MEAN ONSD…………mm
LENS THICKNESS (LT) ON ULTASOUND
RIGHT EYE LEFT EYE
1 1
2 2
3 3
MEAN LT…………mm MEAN LT…………mm
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