3 tonometry and ocular

8/7/2019 3 Tonometry and Ocular

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r mon arnarr mon arnar

With acknowled ements toWith acknowled ements to

Dr RobertDr Robert HarperHarper


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B k r n h n in r i n I PB k r n h n in r i n I P

Glaucoma is characterized by raised IOP, opticneuro a y an amage caus ng v sua e

loss traditional view

progressive optic neuropathy, with a typicallycupped, pale optic disc and a characteristic loss of

sensitivity to light Sponsel in 1980s

a variable combination of raised IOP, optic discchanges and visual field loss Quigley in 1990s

Randomised controlled trial evidence 2000+


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Theories of optic nerve damage

Reduced blood flow/vascular dysregulation

laminar plates

Current view: RGC death is causes b a o tosisand remodelling of the optic nerve head, mediatedby mechanical forces, ischaemia and reperfusion

injury (IOP and OBF implicated in these issues)


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Age

IOP

Race

Diabetes Mellitus

Hypertension

M o ia Corneal thickness


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Background: IOP at presentation:Background: IOP at presentation:

epidemiologyepidemiology

Study No POAG % with

normal IOP

Des Moines, USA 189 68

Ferndale, Wales 20 35Framingham, USA 40 52

Baltimore, USA 194 59

Beaver Dam, USA 104 32Roscommon, Ireland 41 37

Blue Mountains, Aus 108 75


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.

IOP 16-21mmHg ~ 2.5x

IOP 22-29mmHg ~ 13x

Baltimore Eye Study 1991


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ac groun : str ut on oac groun : str ut on o

Av=15.7 mmH

SD=2.7 mmHg

-

str ut on s ewe


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Background: IOP and clinical trialsBackground: IOP and clinical trials

Key randomised glaucoma trialsOHTS, EMGT, CNTGS, CIGTS, AGIS, EGPS

Lowering IOP exerts a favourable influence on the

development and progression of glaucoma Lower IOP means better rotection

Lowering IOP does not always stop progression

-

reduction/progression relationship


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summarysummary

Multi-centre study, 1636 patients with OHT- mm g - yrs, compar ng convers on

rate to glaucoma in Rx versus No Rx

Conversion 4.4% in Rx group and ~9% incontrol rou i.e. no Rx

>90% of OHT pts did not convert after 5 years

, ,predictors for conversion to POAG

CCT was a risk factor for POAG conversion


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stu y summarystu y summary

First treatment versus no treatment RCT in

Population screening 44K 255 pts recruited

Randomised to IOP or no Rx~

IOP reduction reduced progression risk by

~

Lower risk patients and no treatment option


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Typical tonometry referral criteriaTypical tonometry referral criteria

Contact applanation tonometry

IOP >22mmHg with disc changes

IOP >35mmHg (urgent)


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e ear est tonometer

a pat on


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n entat on tonometers

If a plunger of known weight is rested

indentation should (?) be proportional to

Note: ocular rigidity/facility of aqueousoutflow (see separate lecture on

tonometr


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Plunger may be connected to lever arm and

scale (e.g. Schitz) or to electronic recordingsystem (e.g. Mueller)

From Henson (1983)


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c otz

The footplate is rested on the cornea and the

plunger is free to indent the cornea. A varietyof weights may be used to minimise errorsdue to corneal rigidity (use with tables)


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Normal weight (knurled knob above

footplate) = 5.5grams giving total of 16.5grams to be supported by cornea. Additionalweights are 7.5, 10, 15 g


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n entat on

Shiotz o


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sa vantages

50g)

Difficult to disinfect note also CJD risk ?

Displacement of aqueous

Effect of corneal ri idit on readin


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vantages

Cheap Portable

Can measure ocular tension of eye

w scarre cornea


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pp anat on tonometrypp anat on tonometry

Imbert-Fick law IOP = tonometer weight (g) / area (mm2)

Method of choice for tonometry (currently)

Constant area, variable force


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Gambs Cone just touching cornea

3.06 mm black square

3.06 mm diameter


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Difficulty with Gambs


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o mann tonometero mann tonometer

Applanation diameter 3.06 mm

very e u sp ace .

bending force = surface tension

1 gm equiv to 10 mmHg-

- SD of differences


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o mann Doubling prism to separate images by 3.06

mm


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, .comparing calibrate new

instruments.


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Ad


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Advantages

cheap

comfortable (apart from anaesthetic)


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sa vantages

cannot be delegated

contact w t cornea s g t c ance oabrasion)


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rrorsrrors

Lids touching the probe ( IOP)

ur ace ens on orce a ere m n ma

Prolon ed contact IOP

Corneal astigmatism (>3DC)

Incorrect vert cal al gnment ( IOP)

Calibration s stematic or random or Observer errors ( or IOP)

Meniscus width (usually IOP)


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en scus w ten scus w t

Thickness of flourescein ring Ideal ~ 1/10th diameter cone (0.3mm*)

~2mmHg

.

~0.35 mmHg


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er ns


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Hand held

A l h r Portable


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NonNon--contact applanation tonometrycontact applanation tonometry First NCT designed by Grolman and introduced by

American Optical in 1972 r nc p e was cons ere as ear y as y r c

Zeiss

Reichert (formerly American Optical) NCT II and

Keeler Pulsair EasyEye

Nidek NT-2000/4000

-

Canon TX-10


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pr nc p epr nc p e r g na rects an a r-pu towar s t e cornea -

point of applanation detected by optical system, time

electronically (time relates to the IOP)

Later enerations measure air- ulse ressure at

applanation Keeler Pulsair is hand-held and can be used in any

pos t on - creates rampe a r pu se w c automat ca yapplanates cornea at alignment. Optical system detects

.generation instrument is Pulsair EasyEye

Modern NCTs use lower ulse ressure than theoriginal Reichert instrument


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m tat onsm tat ons Some NCT advantages could become limitations

if the user is unaware of the errors that can beintroduced in estimating IOP

See variations in IOP in slides below

Essential to take at least 3-4 readings per eye inorder to balance out the effect of the ocular pulse

NCTs can provide clinically meaningful measuresof IOP which equate to those obtained by theGoldmann instrument

NCT has not replaced GAT as the technique ofchoice in the hospital setting


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actors a ect ngactors a ect ng s ort terms ort term

Time of Day (diurnal range) Normal ~3-6 mmHg

Glaucoma avera e ~13 mmH

Diurnal variation in plasma cortisol (?)

- ,

Repeat tonometry and phasing


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Typical IOP Diurnal Variation in Normals,

showing nocturnal dip.

25

15

10IO

5

0 2 4 6 8 10 12 14 16 18 20 22 0 2 4 6 8 10 12

Time of Day (Hours)


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actors a ect ngactors a ect ng s ort terms ort termArterial pulse

-

Drinking/Fluid intake

Water and coffee +3 mmHg in 20 min alcohol -3mmHg in 5 min

Contraction of extra/intraocular muscle IOP

Accommodation

Blinking and lid squeezing


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actors a ect ngactors a ect ng s ort terms ort termBlood pressure, exertion, posture

sitting to supine 1-6 mmHg increase

nvers on ncreases++ o - mm g

aerobic exercise can lower IOP

straining can increase IOP

ti ht collar or neck tie 4mmH holding breath


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ystem c an ocu ar seaseystem c an ocu ar seaseSystemic disease

association between raised IOP/Glaucoma andsystemic hypertension and DM

the secondary glaucomas!

anterior uveitis and retinal detachments


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Lee at al. The corneal thickness and intraocular pressure story: where are we

now? Clin ExpOphthalmol 2002; 30: 334-337


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ornea t c ness anornea t c ness anPost PRK

7

5

6

Hg)

3

4

tion(m

1

2

O

Predu

0

0 25 50 75 100 125 150 175

I


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ar y correct on actorar y correct on actorCCT

(mm)

10mm

Hg

15mm

Hg

20mm

Hg

25mm

Hg

30mm

Hg

. + . + . + . + . + .

0.48 +2.2 +2.6 +2.9 +3.3 +3.6

. . . . . .

0.52 -0.4 -0.2 +0.0 +0.1 +0.30.54 -1.6 -1.5 -1.4 -1.3 -1.2

0.56 -2.8 -2.8 -2.8 -2.8 -2.7

0.58 -3.9 -4.0 -4.1 -4.1 -4.2

Additive correction (in mmHg) to be added to IOPrea ngs a eren s or eve s o a er

Ehlers et al, 1975).


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ornea t c nessornea t c ness

Knowledge of CCT provides information on

an n v ua s r s an a ows correc on o

IOP (OHTS, Brandt 2004)

No single correction factor is agreed upon. - .

difference from an average CCT is suggested

European Glaucoma Society (2003)


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Choose based on

Validity/Precision

issues

Ease of use

Value for money

ppearance


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eve opments n tonometryeve opments n tonometry

Ocular Res onse AnalyserTonopen

neumatonometry

Pascal D namic Contour tonometer

Integrated tonometer/pachymeter unit


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cu ar esponse na ysercu ar esponse na yser

Reichert ORA

Bi-directional dynamic

Corneal hysteresis:

corneal rigidity,

Clinical trials awaited


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Pascal Dynamic Contour TonometryPascal Dynamic Contour Tonometry

Based on principle of contour

Contour tip concave, with

with contact surface

va ues c a me to e c oserto true manometric levelscompared to GAT

1Kniestedt et al, Archives of Ophthalmology 2004


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onopenonopen

Applanation device with small footprint-

abnormalities

A sterile cover must be over the tip

button until CAL appears in the window

Ensure atient has anaesthetic, entl taTonopen against cornea. Final averagedreading (of usually 4 6) displayed


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neumatonometerneumatonometerResistance to air flow

varies with IOP

3mm diameter area

Back pressure in air

resistance to air flow

Force applied adjusts to maintain

constant area of applanation


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Overcomes some of the problems

Measures

IOP (mmHg) ulse am litude

(mmHg)

ulse volume (l) pulse rate (/min)

ocular blood flow

(l/min)OBF tonometerOBF tonometer


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cont nuous recor ngcont nuous recor ng

14

Hg

13

IOPm

12

11

10

Time (sec)

1 2 3 4 5 6


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cu ar oo ow onometercu ar oo ow onometer

Earl studies su estedhelpful in vascularaetiolo of POAG/NTG

Benefit of OBF now

Still affected by cornel

c ness more anGAT?)

--


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--

Distribution of IOP

Normal and Glaucoma

Distribution of POBF

Normal and Glaucoma

16

18

20

20

25

10

12

14

15

4

6

8

5

10

0

2

8 12 16 20 24 28 32 36 400

100 400 700 1000 1300 1600 More

IOPPOBF


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natomy ys o ogy onatomy ys o ogy o The eye receives its blood supply from 2 sources of

the ophthalmic artery: Ciliary arteries

Central retinal artery

Ciliary supply accounts for 95% of total OBF

Intraorbital (pial arteries and CRA)

Pre-laminar (posterior ciliary arteries)


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pt c nerve oo supp ypt c nerve oo supp y


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et o s o assess nget o s o assess ng

Angiography

Laser doppler velocimetry

Laser doppler flowmetry

Heidelberg Retina Flowmetry (HRF)

Laser speckle phenomenonue e en op cs

Retinal vessel analyser

ornea empera ure Colour Doppler imaging

er p era oo ow

See Flammer et al, Prog Ret Eye Res 2002, 21:359-93.


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n g aucoman g aucomaeren ec n ques measure eren aspec s o

ocular blood circulation and numerous studies have

-groups (see Flammer et al review, 2002)

.

There is reduced OBF in glaucoma that involves differentarts of the e e includin the o tic nerve head retinal

circulation, the retrobulbar and peripheral blood flow

The reduced OBF appears more pronounced in patients

w t The effect of reduced OBF is more pronounced under

. .


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oss e causes o re uct onoss e causes o re uct on

Increased resistance to OBF

Anatomical variations

Vascular dysregulation

ecrease per us on pressure

Due to increased IOP

Due to decreased BP


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an per us on pressurean per us on pressureOcular perfusion pressure (OPP) cannot be

Estimate:

OPP=2/3 mean arterial BP minus IOP

Medical thera directed towards

increasing OPP

qu va en re uc ons may no g ve esame increase in OPP

Perfusion ressure and POAGPerfusion ressure and POAG


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Tielsch et al (1995) Arch Ophthalmol 113:216-221

3 tonometry and ocular

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