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MYOPIA• Short sightedness• Myopia is a greek word meaning *close the eye*• Refractive error I• Parallel rays of light coming from infinity are

focused in front of the retina.• Accommodation is at rest

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Mechanism of production

• Axial • Curvatural • Positional • Index • Myopia due to excessive accommodation

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Optics of myopia • Far point is finite (In front of the eye) • Emmetropic eye it is at infinity• Higher the myopia the shorter the distance• Far point is 1mt from the eye ,there is 1D

of myopia• Nodal point is further away from retina

Accommodation need not develop normally resulting in Convergence insufficiencyExophoria

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TYPES OF CLASSIFICATION

• Clinical Classification

• Degree of Myopia• Age of Onset

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Clinical Classification• Congenital Myopia• Simple Myopia• Degenerative Myopia• Nocturnal Myopia• Pseudo Myopia• Induced Myopia

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Degree of Myopia

• Low Myopia(<3D)• Medium

Myopia(3-6D)• High

Myopia(>6D)

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AGE OF ONSET

• Congenital Myopia• Youth-Onset

Myopia(<20 yrs of age)

• Early Adult-Onset Myopia(20-40 yrs of age)

• Late Adult-Onset Myopia(>40 yrs of age)

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Congenital myopia Frequently seen in Premature babies Marfan’s syndromeHomocystinuria Increase in axial length Increase inOverall globe sizeSince birth, diagnosed at age 2-3 years If unilateral, as anisometropia, may develop

amblyopia, strabismusUsually 8-10 D, remain constantBilateral- difficulty in distant vision, hold things

very close

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Associated conditions Convergent squint CataractMicrophthalmosAniridiaMegalocorneaCongenital Separation of retinaManagement Early Correction is desirable Retinoscopy under full cycloplegia Early full correction desirable Poor prognosis

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• Simple / developmental myopia

Physiological error not associated with any disease of the eye

Etiology :Normal biological variation in development

of eye Inheritence

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Associated factors

Role of diet

Theory of excessive near work

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Clinical picture

Rarely present at birth

Rather born hypermetropic, become myopic

Begins at 7-10 years, stabilizing around mid teens

Usually around 5D, never exceeds 8D

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Symptoms

Poor vision for distanceAsthenopic symptoms develop due to

dissociation between accommodation and convergence

Convergence weakness, exophoria, suppression

Excessive accommodation inducing ciliary spasm and artificially increasing the amount of myopia

Psychological outlook

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Signs

Large and prominentDeep ACLarge, sluggishly reacting pupilsNormal fundus, rarely crescentUsually doesn't exceed 6-8D

• Retinoscopy under full cycloplegia

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• Pathological / degenerative / progressive myopia

Rapidly progressive associated with degenerative changes in the eye

EtiologyRapid axial growth of the eyeball outside

the normal biological variations of development

Role of heredityRole of general growth process

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Genetic factors General growth process

More growth of retina

Stretching of sclera Increased axial length

Degeneration of choroid

Degeneration of retina

Degeneration of vitreous

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Symptoms

Defective vision

Muscae volitantes / floating black opacities

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Signs

EYE Large, prominent eyes simulating exophthalmos

CORNEA large ANTERIOR CHAMBER deep LENS show opacities at the posterior pole

due to aberration of lenticular metabolism and due to overstretching anterior dislocation may also occur

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VITEROUS degeneration,viterous liquefication,vitreous detachment present as WEISS REFLEX

SCLERA thinning resulting in formation of STAPHYLOMA

VISUAL FIELD DEFECTS show Contraction and in some ring scotomas present

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DISC Large in sizeMyopic Crescent on the temporal side of

the discChoroidal CrescentSupertraction of the retina Inverse myopia Myopic crescent situated

nasally and supertraction of the retina temporally

called as INVERSE CRESCENTPeripapillary Atrophy

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MACULA Foster-Fuchs fleck

RETINAL DETACHMENTPOSTERIOR STAPHYLOMARETINAL HOLES TESSELATED FUNDUS

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Treatment Optical treatment

Appropriate concave lenses

Minimum acceptance providing maximum vision

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Guidelines LOW DEGREES OF MYOPIA (Up to -

6D)

IN YOUNG SUBJECTS Defect should never be overcorrected and advised

for constant use to avoid squinting and develop a normal ACCOMMODATION-CONVERGENCE reflex

IN ADULTS Receiving spectacle for the first time,have the ciliary

muscle that are unaccostomed to accommodate efficiently so that lens of slightly lower power(1 or 2 D) may be prescribed for reading,especially if engaged in to any greater extent.Above the age of 40 years,when accommodation fails physiologically, a weaker glass for near work is essential

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HIGH DEGREES OF MYOPIA

Full correction rarely be tolerated so we attempt to reduce the correction as little as is compatible with comfort for binocular vision. We prescribe the lens with which the greatest visual acuity is obtained without distress

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ADVANTAGES OF SPECTACLESEconomicalAllow incorporation of prism,bifocals,pal

which can be used for the management of esophoria or any accommodative disorders accompanying myopia

Spectacles require less accommodation than contact lens for myopia that likelihood of accommodative asthenopia or near point blur in patients approaching presbyopia may be less

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DISPENSING SPECTACLES IN HIGH MYOPIA

• High index lens materials• Lighter lens materials• Reduced eyesize of selected frames• Minus lenticular lens designs

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ADVANTAGES OF CONTACT LENS

• Contact lens provides cosmosis

• Large retinal image size and slightly better visual acuity in severe myopia

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SURGICAL TREATMENT

EpikeratophakiaRKPRK ISCRPhakic IOL’SLASIK

LASIKLASIKPRKPRK

RKRK

ISCRISCR

Phakic IOL’SPhakic IOL’S

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Photorefractive Keratectomy

(PRK)• Involves direct laser ablation of corneal stroma

after removal of corneal epithelium mechanically or using a laser beam.

• Done using Excimer laser• MUNNERLYN EQN: depth of ablation

(micrometer)=[diameter of optical zone(mm)]² × 1/3power(Diopter)

• For myopic a large amount of ablation is done in central cornea than in the periphery.

• Give good results for -2D to -6D of myopia

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LASIKLaser Assisted In situ

Keratomileusis• Method:Anterior flap of cornea is lifted with a keratome and

excimer laser is used to sculpt the stromal bed to change the refractive error of eye

• Corrects 0.5 to 12D of myopia and upto 8D of astigmatism• Guidelines:Age more than 18yrs BCVA better than 6/12 Stable refraction for last 1yr Absence of corneal disease & ectasia• Note:• (1) In no case the residual bed thickness after the ablation

should measure 250microns so as to avoid central corneal ectasia

• (2) Ideally the ablation should be done within 30sec of the preparation of flap

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LASEKLaser subepithelial

Keratomileusis• Indications:• Low myopia• Irregular astigmatism• LASIK complications in contralateral eye• Thin corneal pachymetry• Predisposition to trauma• Glaucoma suspect

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• Method:• Simple inexpensive procedure that

involves creation of epithelial flap after exposure to 18% alcohol for 25sec & subsequent replacement of flap after laser ablation

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RKRadial Keratotomy

• It refers to making deep corneal incisions(initially 16,now down to 4) in the peripheral part of cornea leaving about 4mm central optical zone

• The incisions are made almost down to the level of Descemet’s Membrane

• These incisions on healing flatten the central cornea thereby reducing its refractive power

• For low to moderate degree of myopia(-1.5 to -6D of myopia)

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Epikeratophakia• For high degree of myopia (upto 20D)• Method:• The epithelium is removed & then a

pocket is fashioned under the edge of the remaining epithelium & into this is inserted the cryolathed donor homograft

• Preserved material can also be used

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NON CORNEAL INTERVENTIONS

• (A) REMOVAL OF CLEAR LENS• We know that an aphakic eye is strongly hypermetropic • If an eye with an axial myopia of -24D is deprived of its

lens it will become emmetropic without any correcting lens

• Note:• Whenever surgery on clear lens is contemplated the

eye is examined thoroughly for abnormalties like Raised IOP,Vitreous & retinal degeneration etc

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• (b)Phakic intraocular lenses• An IOL of appropriate power is implanted

inside the eye without touching normal crystalline lens thus without disturbing accomodation

• Method can be used to correct both myopia & hypermetropia

• Phakic IOL types:• PC IOL• Angle supported IOL• Iris claw lens

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INTRA CORNEAL RING(ICR) IMPLANTATION• ICR implantation into the peripheral

cornea approx.upto 2/3rd of stromal depth can also be considered for correction of myopia

• It results in a vaulting effect that flattens the central cornea decreasing the myopia

• The procedure has the advantage of being reversible

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For Further Queries Contact :Ms. Priyanka SinghHead – Optometry ServiceEmail –

optometry@venueyeinstitute.org

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