myopia
TRANSCRIPT
MYOPIA
SHORT SIGHTEDNESS
DIOPTERIC CONDITION IN WHICH INCIDENT PARALLEL RAYS COME TO A FOCUS ANTERIOR TO THE LIGHT SENSITIVE LAYER OF RETINA WITH ACCOMODATION AT REST.
MYOPIA
1. AXIAL MYOPIA COMMONEST FORM INCREASE IN ANTERO-POSTERIOR LENGTH OF THE
EYEBALL
2. CURVATURAL MYOPIA INCREASED CURVATURE OF CORNEA, LENS OR BOTH
3. POSITIONAL MYOPIA PRODUCED BY ANTERIOR PLACEMENT OF CRYSTALLINE
LENS IN EYE
4. INDEX MYOPIA INCREASE IN THE REFRACTIVE INDEX OF CRYSTALLINE
LENS ASSOCIATED WITH NUCLEAR SCLEROSIS
5. MYOPIA DUE TO EXCESSIVE ACCOMODATION SPASM OF ACCOMODATION
ETIOLOGICAL CLASSIFICATION
1. Congenital myopia2. Simple or developmental myopia3. Pathological or degenerative myopia4. Acquired myopia which may be
Post traumatic Post keratitic Drug induced Pseudomyopia Space myopia Night myopia Consecutive myopia
CLINICAL VARIETIES
Since birthDiagnosed by 2-3 yearsMostly unilateralManifests as anisometropiaChild may develop convergent squint in order to
preferentially see clear at its far point (10-12cms)
CONGENITAL MYOPIA
Associated with cataract, micropthalmos, aniridia, megalocornea, congenital separation of retina.
Developmental myopia- commonest varietySchool myopia (school going age 8-12 years)Etiology
Axial type: physiological variation in length of eye ball precocious neurological growth during childhood
SIMPLE MYOPIA
Curvatural type Underdevelopment of eye ball
Role of diet in early childhoodRole of genetics
Prevalence in children both parents myopic(20%) One parent myopic(10%) No parent myopic(5%)
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
DiagnosisConfirmed by performing retinoscopy
Degenerative/ progressive myopiaRapidly progressive error which starts in
childhood at 5-10 years of ageHigh myopia in early adult life with
degenerative changes
PATHOLOGICAL MYOPIA
Role of heredity Heredity linked growth of retina is the
determinant in developmental myopia Sclera due its distensibility follows retinal
growth but choroid undergoes degeneration due to stretching, which in turn causes degeneration of retina Progressive myopia is
Familial More common in chinese,japanese,arabs and
jews Uncommon among negroes,nubians and
sudanese
ETIOLOGY
Role of general growth processLengthening of the posterior segment of globe commences only during the period of active growth and ends with termination of active growth
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 visionMuscae volitantes
Floating black opacities in front of eyes Degenerated liquified vitreous
Night blindness
SYMPTOMS
Prominent eye balls Elongation of eye ball mainly affects posterior
pole and surrounding areaCornea-largeAnterior chamber -deepPupils-slightly large ,react sluggishly to light
SIGNS
Fundus examination:Optic disc
large and pale Temporal edge presents a characteristic myopic crescent Peripapillary crescent encircling the disc may be present, where
choroid and retina is distracted away from disc margin Super traction crescent may be present on nasal side (retina
pulled over disc margin)
Degenerative changes in retina and choroid
Common in progressive myopia Characterized by 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 choroidal haemorrhage• Present at macula
• CYSTOID DEGENERATION – at periphery• Advanced cases:
Total retinal atrophy in central area
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 include: Liquefaction Vitreous opacities Posterior vitreous detachment(PVD)- Weiss’ reflex
Visual fields Contraction Ring scotoma may be
seenERG reveals subnormal
electroretinogram due to chorioretinal atrophy
Retinal detachmentComplicated cataractVitreous haemorrhageChoroidal haemorrhageStrabismus fi xus convergence
COMPLICATIONS
Optical treatment of myopia Concave lenses Basic rule – minimum acceptance providing
maximum visionModes of prescribing concave lens-1. Spectacles2. Contact lens
TREATMENT OF MYPOIA
Contact lenses are used in case of high myopia as they avoid peripheral distortion and minifi cation produced by strong concave spectacle lens
Radial keratotomy 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 photoablated using excimer laser (193nm uv flash) to cause flattening of central cornea
Correction for -2 to -6D of myopia
Disadvantages:Post operative recovery is slowPain and discomfortResidual corneal haze in centre affecting visionExpensive
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 years2. Stable refraction for at least 12 months3. Motivated patient4. Absence of corneal pathology
Absolute contraindication for LASIK Presence of ectasia Corneal thickness <450mm
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 Epiedge Epikeratome
Devoid of complications related to corneal stromal flap
Minimal or no postoperative painRecovery of vision is very early as compared to
PRKNo risk of perforation during surgery and
rupture of globe due to trauma like RKNo residual haze unlike PRK where subepithelial
scarring may occurLASIK is eff ective 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 operationMyopia of -16 to -18D in unilateral casesClear 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
Into the peripheral cornea at approximately 2/3rd stromal depth
Flattening of central cornea, decreasing myopiaAdvantage: reversible procedure
INTRACORNEAL RING (ICR) IMPLANTATION
A non-surgical reversible method of molding the cornea with overnight wear unique rigid gas permeable contact lenses
Myopia correction upto -5DUsed in patients below 18 years of age
ORTHOKERATOLOGY
General measures : Balanced diet rich in vitamins and proteins Early management of associated debilitating disease
Low vision aids indicated in patients with progressive myopia with
advanced degenerative changesProphylaxis Genetic counselling