myopia refractive error

Myopia

DR. MEENANK

1. Definition

2. Etiology

3. Optics

4. Classification

5. Clinical varieties in detail

6. Treatment

Definetion

Myopia ( short sight ) condition where parallel rays come to focus in front of the sentient layer of retina when accommodation is at rest

Muopia (Greek) = To close the eye

History

Kepler (1611), Plempius (1632) - lengthening of posterior part.

Donders (1866) est.. Pathological basis, and detail clinical manifestation's

Etiology Axial : most commonest

1mm = 3D

Curvatural : cornea thickness causes astigmatism

1mm = 6D

eg : ectasies

conical cornea

lenticular curvature

eg : ant/post lenticonus – marked

Positional : dislocation of lens

Myopia due to excessive accommodation - spasm of accommodation,

suspensory lig. Rupture

Index myopia : change in the R.I of the crystalline lens

eg : Nuclear Sclerosis,

Incipient Cataract,

Diabetes.

Buphthalmos : cong/ infantile glaucoma.

Defective development – A.P diameter enlarged and

myopia not in ratio

Optics

Optical system – eye too powerful for axial length

Image of distant object on retina are circles of diffusion form by divergent beam

Far point is finite pt in front of eye – object at far pt focused without acc.

Angle of alpha –ve resulting in convergent squint

Accommodation- uncorrected- not developed , as not needed for Nv. Thus may develop exophoria, convergence insufficiency and presbyopia

Enlarged image is cause of nodal pt being far away from retina

Classification

myop

ia

Congenital myopia

Simple (or) Developmental

myopia

Pathological (or) Degenerative myopia

Acquired myopia

Congenital myopia

Since birth

Diagnosed – 2 -3 yrs.

Associated – prematurity, birth defects, congenital squint, and axial length

Unilateral or bilateral

Unilateral – manifest as anisometropia

diagnosed - after squint- amblyopia

Associated – cataract, microphthalmas, cong. Retinal separation, megalo-cornea

Prognosis – early detection

no 6/6 uni-ocular

Simple Myopia

Physiological / developmental / school

Biological variation in development

Limited progression no disease

Factors associated : Axial – A.P diameter (or) neurological

Curvatural – underdevelopment of eye ball

Diet – poor nutriention

Genetic influence – one (or) both parents

Simple Myopia

Physiological – A/S normal along with normal fundus

Intermittent – early signs of globe enlargement temporally

Sever category of intermittent – crescent with super-traction of disc

course

Born hyper metropic Emmetropic

• overshoot

Myopic

• 7-10 yrs

Stabilized at teens

• -5D to -8D

symptom's :

Poor distance vision – beyond far point impaired

Asthenopic sympt – eye strain due to difference b/w convergence and accommodation

Nv -No accommodation – convergence weakness – exophoria – suppression of one eye

Nv –convergence – excessive accommodation – ciliary spasm

Physiological out-look – myopic child behavior

Signs Eye – large and prominent

A.C. – deep

Pupil – large and sluggish

Fundus – normal

Error - -5.00 D to -8.00D

Diagnosis –visual acuity

subjective testing

retinoscopy

Pathological Myopia

Degenerative / progressive

2-3 %

More marked, high degree

Hereditary

Postnatal

Inc. progressive

Prevalence –

earlier and higher in females

higher – Asians, Arabs, Jews

lower – Africans, Caucasians

more in urban populations

Etiology

Results from rapid growth of eye out side its biological variation

2 theories

- Hereditary

- General growth Genetic factors

Retinal growth Scleral

stretchingIncrease in axial length

Pathological myopia• Degeneration – choroid, retinae,

vitreous

Symptoms Diminished Vn – progressive due to degeneration

Muscae volitantes – deg. lig. Vitreous

Night blindness – high myopes with choroidi-retinal changes

Signs Prominent, elongated(post), unilateral, stimulating

exophthalmos

Cornea – large; A.C – deep; pupil – large, sluggish

Refractive error – by -4D/yr up to 20-30yrs

Fundus – Generalized atrophy of choroid and retinae

Loss of RPE- fundus tugroid- prominent choroidal vessels

Choroid disappears – visible sclera – atrophic patch - post. Pole – macula (common)

Foster – Fuchs's spots – rare, sudden, dark pig.

sub-retinal neovascularization and choroidal hx.

Cystoid degeneration at periphery

Advance cases – total retinal atrophy, central

Lattice degeneration/ snail track lesion

Optic disc Myopic crescent – from elongation of disc

separation of retina and choroid from temp

may be annular

Super traction crescent – nasal retina extending over the disc – blur margin

Posterior staphyloma – higher degree,

herniation of post. Pole – sudden kinking of vessels at margin as in glaucoma

Vitreous – degeneration, PVD-Wiess reflex, liquefaction, opacities

Visual field – ring scotoma

Electo-retinograph – chorioretinol atrophy

Complications retinal tears, detachment, Hx (high myopia)

vitreous detachment, degeneration

complicated cataract –↓ lenticular metabolism

Nuclear sclerosis – common, effects refraction

Choroidal Hx – sever Vn loss if in fovea

POAG – not common but seen

acquired index – nuclear sclerosis, incipient cataract, diabetic myopia

Curvatural – true inc. in corneal curvature (or) lenticular

Positional – subluxation(ant) of lens

Consecutive – surgical overcorrection(cataract/ hypermetropia)

Pseudo-myopia – due to excessive accommodation and spasm of accommodation

Space myopia – no stimulus for Nv, its variable, trouble in flying and in fog

Night/twilight – shift from photic to scotopic vn is associated with inc. sensitivity to shorter wavelength viz myopic

Drug induced - Cholinergic – pilocarpine, echothiosulphate

Steroid – show changes in crystalline lens

Sulplanamides – changes the refractive indices in media

Diagnosis

presentation Simple – blurred Dv, constant/ transient, Nv may be normal, co-existing condt.

Nocturnal – blurred Dv in dim illumination, difficulty in driving

Pseudo myopia – transient Dv blur, inc after near work

Degenerative - considerable Dv blur, flashes/ floaters, Vn loss

Induced – transient Dv blur until drug effect, pupils constricted – cholinergic antagonist

Ocular examination

Visual acuity – both unaided Nv and Dv should be measured-mean gives reduced V.A

Refraction – retinoscopy or and A.R. , but A.R not qualitativeretinoscopy – diagnosis for nocturnal myopia with cyclopegics

Ocular motility, binocular Vn, accommodation – heterophoria, versions, accommodative facility test

systemic and ocular health – IOP, SLB, post-segment

Special test Fundus Photography

A and B scan

Visual field

Fasting blood sugars

Treatment

Optical Correction Proper correction with concave lens for image to fall on retina

Myopia up to -6.00D Children – full correction

Young adults – prevent over correction

Adults - ↓ 30 yrs. – full correction

↑ 30 yrs. – under corrected – ciliary muscles fail to accommodate

Spectacle's

Economical, safe

Allow incorporation

Better correction of astigmatism

Less acco- near pt. blur in presbyopia

Contact lens

Larger retinal image

Better Vn in Sr. myopia

Better visual field

Dec. prismatic effect

Rigid lens dec. progressive myopia

Surgical Treatment

Incisional – Radial Keratotomy

Lamellar corneal refractive Sx

Freeze keratomileusis of Barraque for myopia obsolete

Non-freeze keratomileusis

Keratomileusis insitu

Automated lamellar keratoplasty

Laser-based corneal refractive Sx

Photorefractive keratectomy (PRK)

Laser insitu keratomileusis (LASIK)

Custom Laser insitu keratomileusis (C-LASIK)

Epithelial Laser insitu keratomileusis (E-LASIK)

Miscellaneous corneal refractive Sx

Orthokeratology

Intracorneal contact lens

Intra stromal corneal ring segment

Intra ocular refractive procedure's

Phakic refractive lens

Refractive lens exchange

Radial keratotomyPhotorefractive keratectomy LASIK

Intraocular refractive procedure's

Radial keratotomy Deep radial incisions (90% thickness) sparing central 4mm –

cornea flatter's on healing

Disadvantages – globe rupture, irregular astigmatism, glare, bullous keratopathy

Photorefractive keratectomy (PRK)

De-epithelialzation – photo ablative0.5.1.0mm morePrevent extreme drying or wetting of cornea and residual islands

Ablation – 6mm for myopiaHand held ring for centration Laser should be coaxial with pupilToric photoabalation

corneal curvature shifts as ant stroma collapse and thins

Intrastromal PPk – double NdYAG Plasmamediated photodistribution shock wave

Complications – decentationCorneal haze, infiltrates, ulcersNight glare , halosDelayed epi healingIslands, Hx, IOP↑

First refractive procedure to use the excimer laser Max success in myopia Good for -2.00D to -6.00D Photoabalation of central optical zone of ant.

Corneal stroma

Combination – Incisional & Ablative Procedure

LASIK - Laser In Situ Keratomileusis

Microkeratome to make a corneal flap – excimer to ablate the refractive error

adv – bilateral, PRK healing risks avoided, stable results

Dis-adv – flap related, striae, diffuse lamellar keratitis, under (or) over correction

LASEK – LASER Epithelial Keratomileusis Similar to PRK – epithelium is removed and replace post Sx

Alcohol to store the epithelium

For large pupils and thin corneas

For > -8.00 D

Adv – no risk of flap dislocation (LASIK)

Thin flap

Less chance of ectasia

Dis- adv – visual recovery slower than LASIK

Epi LASIK Newer version of LASEK- advantage on LASIK

Cleaves epi from bowmen's – structural integrity maintained

More thin flap, less haze, faster recovery

Custom LASIK Customized for each eye

Less halos and glare, More chance of 6/6

Wave front aberrometer - corneal topography

Ablation – flexible laser system

Intra ocular refractive Sx

Refractive lens exchange Existing cataract and cornea unfit for refractive

Sx

For -16.00D to -30.00D

PCO reduced

Accommodation retained thrgh ‘hinges’

Phakic IOLs Patients not qualified for refractive Sx

Ant / Post chamber lens with out removing crystalline lens

Made of plastic (or) silicone

Management flow chart

Patient history and examination

Supplemental testing Assessment and diagnosis

Patient counseling and education

Treatment and management

Simple myopia

Correction

Infants and toddlers – no correction < 3DPre-school/early-school – correct if

>1-2DAdolescent's/

adults – correct significantly

Controlplus lens for NvRigid contact

lensVisual hygiene

ReductionCorneal

modification – refractive

Sx

Nocturnal myopia

Myopia correction for night

time seeing only

Pseudo-myopia

Reduction of accommodative

response – vision therapy,

plus lens for Nv, cycloplegic

agents, visual hygiene

Degenerative myopia

Correction and

management of retinal

changes

Induced myopia

Identification and

treatment of causative

agent

If a man is called to be a street sweeper,

he should sweep street so well that all the

host of heaven and earth will pause to

say, here lived a great street sweeper

who did his job well.

- Martin Luther King, Jr.