BY: ACHIN PANT 3RD YEAR

MBBS

MYOPIAI

t is a refractive state of eye in which parallel rays of light coming from infinity are focused in front of retina, when accommodation is at rest

It is otherwise known as “short-sightedness”

GENERAL EYE MEASUREMENTS IN MYOPIA

Mean corneal power is 1D>emmetropes & hypermetropes

Mean chamber depth is 3.67mm(2.8-4.55)

Mean lens power is 17-35D

Range of axial length: 21.62-26.37mm(low myopia)

21.88-34.77mm(high myopia)

CLASSIFICATION

ETIOLOGICALA

XIAL MYOPIAC

URVATURAL MYOPIAP

OSITIONAL MYOPIAI

NDEX MYOPIAD

UE TO EXCESSIVE ACCOMODATION

AXIAL MYOPIA Results from increase in AP length of the globe

CURVATURE MYOPIA Increased curvature of cornea

POSITIONAL MYOPIA Anterior displacement of crystalline lens in the eye

INDEX MYOPIA Increase in the refractive index of crystalline lens

DUE TO EXCESSIVE ACCOMMODATION

Inpatients with spasm of accommodation

CLINICALC

ONGENITAL MYOPIAS

IMPLE(LOW MYOPIA)I

NTERMEDIATE (MEDIUM, MODERATE MYOPIA)P

ATHOLOGICAL MYOPIAC

HILDHOOD(SCHOOL MYOPIA)A

CQUIRED MYOPIA

CONGENITAL MYOPIA•P

resent since birth•U

sually diagnosed at the age of 2-3 yrs•M

ostly unilateral, manifests as ANISOMETROPIA•C

hild may develop convergent squint•E

rror is about 8-10D remains constant•I

t may be associated with congenital anamolies like cataract, aniridia, micropthalmos, megalocornea etc.

SIMPLE MYOPIAD

evelopment of eye is normalI

t occurs because there is a correction failure between total refractive power(of lens and cornea)& normal axial length

Most eyes have around <3D, some have around 3-5D

Crescent formation is absent in the fundus

Axial length is about 22mm-25.5mm

ETIOLOGYP

hysiological variation in the length of the globe

Role of diet

Pedigree analysis

Excessive near work

Clinical featuresSYMPTOMS SIGNS

Poor distant vision Prominent eyeballs

Asthenopic symptoms Anterior chamber deeper than normal

Half shutting of eyes in children Pupils large and sluggishly reacting

Fundus is normal

INTERMIDDIATE MYOPIAT

erm given by “OTSUKA”I

n these cases posterior segment expansion is greater than normal

Probably an exaggerated enlargement of the normal postnatal distension of the oro equitorial zone

Heredity and environmental factors interact to produce this abnormality

Axial length of globe is 25.5-32.5mm

Most commonly found in the eye with 3-8D of myopia

Incidence of glaucoma & retinal detachment are increased in these cases

Unlike pathological myopia, here eyes however do not have posterior staphyloma

PATHOLOGICAL MYOPIA•I

t is defined as occular disease in which a number of serious complication are associated with excessive axial elongation of the eye

•It is an autosomal recessive trait

•Most cases of myopia related blindness & it is essentially hereditary disease

•“sine-qua-non” of this disease is presence of posterior staphyloma……or k/s SCARPA’s staphyloma

•Decreased scleral resistance & increased expansion forces results in staphyloma formation

Refractive error usually above 6-8D & it’s a degenerative change

Axial length is over 32.5mm in almost all cases

It starts at childhood at 5-10 yrs of age and results in high myopia in early adult life

ETIOLOGYMAINLY TWO MAIN THEORIES ARE GIVEN 1)Role of heredity2)Role of growth process

ROLE OF HEREDITYI

t is now confirmed that genetic factors play a major role in the etiology

It is believed that heredity linked growth of retina is the determinant in the development of myopia

ROLE OF GENERAL GROWTH PROCESS

The factors such as nutritional deficiency, debiliating diseases and indifferent general health which effect the general process will also influence the progress of myopia

Genetic factors

More growth of retina

Stretching of sclera

Increased axial length

Degeneration of choroid

Degeneration of retina

Degeneration of vitreous

Symptoms 1.D

efective vision2.M

uscae volitantes3.N

ight blindness

signs1.P

rominent eye balls2.C

orneal thinning, anterior iris insertion3.A

nterior chamber is deep, scleral fibers are of small dimension

4.Choroidal vascular occlusion

5.Pupils is slightly large and react sluggishly to light

FUNDAL CHANGES•O

ptic disc appears large and pale and at its temporal edge a characteristic myopic crescent is present

•Degeneration changes in retina & choroid are common in progressive myopia

•In peripheral retina there is attenuated cystoid changes with formation of “BLESSIG-IWANHOFFS CYSTS”

•FOSTER-FUCHS’ spot may be present at the macula

•Lamina vitrea shows thinning splitting & rupture clinically seen as “laquer cracks”

•Posterior staphyloma due to ectasia of sclera at posterior pole may be apparent as an excavation with the vessels bending backward over its margins

•Optic nerve is oval & cup-disc ratio is increased

•Degenrative changes in vitreous include liquefaction, vitreous opacities & posterior vitreous detachment appears as WEISS’ reflex

•Visual fields show contraction and in some cases ring scotoma is present

•ERG reveals subnormal electroretinogram due to chorioretinal atrophy

COMPLICATIONSR

etinal detachmentC

omplicated cataractV

itreous hemorrhageS

trabismus fixus convergence

CHILDHOOD MYOPIAI

ts is otherwise k/s school myopiaO

ccurs at 5-12 yrs of ageT

ends to demonstrate earlier and may continue upto 3rd decade

DONDERS recognised two types of childhood myopia

1) stationary type

2) progressive type

AQUIRED MYOPIAP

ost- traumaticP

ost-keratiticD

rug inducedP

seudomyopiaS

pace myopiaN

ight myopiaC

onsecutive myopia

INVESTIGATIONSV

isual acuityF

undus examinationR

etinoscopyI

ntraocular pressureI

nvestigations to rule out any systemic disorder like DM, TB etc..

TREATMENTA

IM:

1.Prevention of myopia from development

2.Prevention of myopia progression, management of complications & visual rehabilitation

OPTICAL TREATMENT

SURGICAL TECHNIQUES

LOW VISION AIDS

GENETIC COUNSELLING

1. OPTICAL TREATMENTI

t constitutes prescription of appropriate concave lenses, so that clear image is formed on retina

At the same time

Corrected by concave lenses

2. SURGICAL TECHNIQUESP

hotorefractive keractectomyL

aser in-situ keratomileusisE

xtraction of clear crystalline lensP

hakic intraocular lensI

ntercorneal ring transplantationo

rthokeratology

PHOTOREFRACTIVE KERATECTOMY

In this technique a central optical zone of anterior corneal stroma is photoablated by using excimer laser(193nm UV flash) to cause flattening of central cornea

It provides good correction for -2 to -6D of myopia

LASER IN-SITU KERATOMILEUSISI

t is widely accepted treatment modality among all choices

It can correct myopia upto -12D

PATIENT SELECTIONP

atient above 21 years of ageW

ho have suitable refractive error above 12 monthsW

ho have had unsatisfactory results with non-surgical treatment

In whom corneal thinning disorders that lead to curvature myopia such as keratoconus have been ruled out

ADVANCES IN LASIKC

USTOMIZED LASIK: C-LASIK is based on the wave front technology

It corrects abberations present in the eye alongwith spherical & cylindrical corrections

E-LASIK: in this technique instead of corneal stromal flap only the epithelial sheet is separated mechanically with the use of a customized device

ADVANTAGESM

inimal or no postoperative painR

ecovery of vision earlyN

o risk of perforation of globeN

o residual hazeE

ffective in correcting myopia of abt -12D

DISADVANTAGESE

xpensiveR

equires greater surgical skillF

lap related complications more

EXTRACTION OF CRYSTALLINE LENS

“FUCALA’S OPERATION”

Employed for myopia upto -16 to -18D mostly in unilateral cases

Recently extraction o lens and implantation of IOL is done to correct myopia> 12D

PHAKIC IOLI

n this technique a special type of intraocular lens is implanted in anterior or posterior chamber anterior to the natural crystalline lens

Correction can be done for myopia>12D

INTRACORNEAL RING IMPLANTATION

Into the peripheral cornea at 2/3rd stromal depth

It has a vaulting effect which flattens the central cornea decreasing myopia

It’s a reversible process

ORTHOKERATOLOGYI

t’s a non surgical procedure in which moulding of cornea takes place by overnight wear unique rigid gas permeable lenses are used

It can correct myopia upto -5D

3. LOW VISION AIDSU

sed for progressive degenerative myopia where vision cant be corrected by lens and spectacles

4. GENETIC COUNSELLINGG

enetic counselling regarding heredity of myopia should be explained to the patients

BIBLIOGRAPHYO

PHTHALMOLOGY-SHORT TEXTBOOK(GERHALD.K.LANG)

CLINICAL METHODS IN OPHTHALMOLOGY(SANDEEP SAXENA)

PARSONS’ DISEASES OF EYE

A. K. KHURANA