MYOPIA

PRESENTER – DR. OM PATEL

MODERATOR – DR. SURYAKANT JHA

SHORT SIGHTEDNESS

Condition in which incident parallel rays come to a focus anterior to the light sensitive layer of retina with accomodation at rest .

MYOPIA

OPTICS OF MYOPIA

The optical system is too powerful for its axial length

Image of distant object on retina is made up of circle of diffusion formed by divergent beam since the parallel rays of light coming from the infinity are focused in front of the retina

Far point is finite point in front of eye

OPTICS OF MYOPIA

Accommodation in uncorrected myopes is not developed normally

May suffer from convergence insufficiency and exophoria

Early presbyopia

ETIOLOGICAL CLASSIFICATION

Axial : most commonest

1mm = 3D

Curvatural :

Increased corneal or lens curvature

1mm = 6D

Positional : Dislocation of lens

Myopia due to excessive accommodation : Spasm of accommodation,

Suspensory lig. Rupture

ETIOLOGICAL CLASSIFICATION

Index myopia :

Change in the R.I. of the crystalline lens

eg : Nuclear Sclerosis,

Incipient Cataract,

Diabetes.

ETIOLOGICAL CLASSIFICATION

DEGREE OF MYOPIA

Low Myopia(<3D)

Medium Myopia(3-6D)

High Myopia(>6D)

Congenital myopia

Simple or developmental myopia

Pathological or degenerative myopia

CLINICAL VARIETIES

Frequently associated with Premature babies Marfan’s syndrome Homocystinuria

Since birth,Diagnosed by 2-3 years

Increased axial length, overall globe size

If unilateral may produce amblyopia, strabismus

Bilateral – difficulty in distant vision, holds things closer

Usually error is 8-10 D, remains constant

CONGENITAL MYOPIA

Associated with

Cataract

Micropthalmos

Aniridia

Megalocornea

Congenital separation of retina

Management

Early full correction

Retinoscopy under full dilatation

CONGENITAL MYOPIA

Developmental myopia- commonest variety

School myopia (school going age 8-12 years)

Physiological, not associated with any eye disease

Normal biological variation in development

Rarely present from birth, rather hypermetropiafollowed by myopia

SIMPLE MYOPIA

Symptoms Poor vision for distance(short sightedness)

Asthenopic symptoms

Half shutting of eyes

CLINICAL PICTURE

Signs Prominent eyeballs

Anterior chamber - deeper than normal

Pupils- Large, sluggishly reacting

Fundus- normal; rarely temporal myopic crescent may be seen

Magnitude of refractive error Increasing at rate -0.5 +- 0.30/ year.

Does not exceed -6 to -8 D

DiagnosisConfirmed by performing retinoscopy

Degenerative/ progressive myopia

Rapidly progressive myopia associated with degenerative changes

Starts in childhood at 5-10 years of age

PATHOLOGICAL MYOPIA

ETIO-PATHOGENESIS

Genetic factors (play major role)

General growth process(minor)

More growth of retina

Stretching of sclera

Increase axial length

Degeneration of choroid

Degeneration of retina

Degeneration of vitreous

Defective vision

Muscae volitantes

Floating black opacities in front of eyes

Degenerated liquified vitreous

SYMPTOMS

Prominent eye balls

Elongation of eye ball mainly affects posterior pole and surrounding area

Cornea-large

Anterior chamber –deep

Pupils-slightly large,react sluggishly to light

Lens Opacities at the posterior pole due to aberration of lenticular metabolism

Anterior dislocation due to overstretching

SIGNS

Fundus examination:Optic disc

Large and pale

Temporal edge presents a characteristic MYOPIC CRESCENT

SUPER TRACTION CRESCENT may be present on nasal side (retina pulled over disc margin)

Peripapillary crescent encircling the disc may be present, where choroid and retina is distracted away from disc margin

Degenerative changes in retina and choroid

White atrophic patches at macula with a little heaping of pigment around them

• FOSTER-FUCH’S SPOT:• Dark red circular

patch due to sub-retinal neo vascularization and choroidalhaemorrhage

• Present at macula

• CYSTOID DEGENERATION – at periphery

Posterior staphyloma Due to ectasia of sclera at posterior pole

It may be apparent as an excavation with vessels bending backward over margins

Degenerative changes in vitreous Liquefaction

Vitreous opacities

Posterior vitreous detachment(PVD)- Weiss’ reflex

Visual fields Contraction

Ring scotoma may be seen

ERG reveals subnormal electroretinogram due to chorioretinal atrophy

Retinal detachment

Complicated cataract

Vitreous haemorrhage

Choroidal haemorrhage

Strabismus fixus convergence

COMPLICATIONS

Optical treatment of myopia Concave lenses

Basic rule – minimum acceptance providing maximum vision

Modes of prescribing concave lens-

1. Spectacles

2. Contact lens

TREATMENT OF MYOPIA

Contact lenses are used in case of high myopia as they avoid peripheral distortion and minification produced by strong concave spectacle lens

Radial keratotomy

Photo-Refractive keratectomy (PRK)

LASIK

Fucala’s lens extraction

ICL (Implantable Collamer Lens) or Phakic IOL

ICR ( Intra Corneal Ring implantation)

Orthokeratology

SURGICAL TREATMENT OF

MYOPIA

Radial keratotomy Obsolete now a days

Making deep radial incisions in peripheral part of cornea leaving the central a 4mm optical zone

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

Correct low to moderate myopia(2-6D)

DISADVANTAGES:

Cornea is weakened – globe rupture in sports persons

Uneven healing – irregular astigmatism

Patient may feel glare at night

SURGICAL TREATMENT OF

MYOPIA

Photo refractive keratectomy (PRK)

A central optical zone of anterior corneal stroma is photoablatedusing excimer laser (193nm uv flash) to cause flattening of central cornea

Correction for -2 to -6D of myopia

Disadvantages:

• Post operative recovery is slow

• Pain and discomfort

• Residual corneal haze in centre affecting vision

• Expensive

Refractory surgery of choice for myopia of upto -12D

LASER ASSISTED IN-SITU KERATOMILEUSIS(LASIK)

Flap of 130-160 micron thickness of anterior corneal tissue is raised

Midstromal tissue is ablated directly with an excimer laser beam

ultimately flattening the cornea

1. Patients >20 years

2. Stable refraction for at least 12 months

3. Absence of corneal pathology

Absolute contraindication for LASIK Corneal thickness <450 micrometers

Presence of ectasia

PATIENT SELECTION CRITERIA

Customised(C)-LASIK:

Based on wave front technology

Corrects spherical, cylindrical and other aberations present in eye

Gives vision beyond 6/6 i.e.,6/5 or 6/4

ADVANCES IN LASIK

Epi-(E) LASIK:

Only epithelial sheet is separated with EpiedgeEpikeratome

Devoid of complications related to corneal stromal flap

Minimal or no postoperative pain

Recovery of vision is very early as compared to PRK

No risk of perforation during surgery and rupture of globe due to trauma like RK

No residual haze unlike PRK where subepithelialscarring may occur

LASIK is effective in correcting myopia of -12D

ADVANTAGES OF LASIK

Expensive

Requires greater surgical skill than RK and PRK

Flap related complications

Intraoperative flap amputation

Wrinkling of flap on repositioning

Postoperative flap dislocation/subluxation

Epithelization of flap – bed interface

Irregular astigmatism

DISADVANTAGES

Fucala’s operation

Myopia of -16D to -18D in unilateral cases

Clear lens extraction with intraocular lens implantation of appropriate power is the refractive surgery for myopia of >-12D

EXTRACTION OF CLEAR CRYSTALLINE LENS

Intraocular contact lens implantation for correction of myopia of >-12D

Special type of IOL is implanted in anterior chamber or posterior chamber anterior to natural crystalline lens

PHAKIC INTRAOCULAR LENS(ICL)

Into the peripheral cornea at approximately 2/3rd

stromal depth

Flattening of central cornea, decreasing myopia

Advantage: reversible procedure

INTRACORNEAL RING (ICR) IMPLANTATION

A non-surgical reversible method of moulding the cornea with overnight wear unique rigid gas permeable contact lenses

Myopia correction upto -5D

Used in patients below 18 years of age

ORTHOKERATOLOGY