Myopia

Myopia- Definition, etiology, classification, Clinical varieties, management and treatment

1. Myopia

2. 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

3. AXIAL MYOPIA COMMONEST FORM INCREASE IN ANTERO-POSTERIOR LENGTH OF THE EYEBALL 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

4. Congenital myopia Simple or developmental myopia Pathological or degenerative myopia Acquired myopia which may be Post traumatic Post keratitic Drug induced Pseudomyopia Space myopia Night myopia Consecutive myopia CLINICAL VARIETIES

5. Since birth Diagnosed by 2-3 years Mostly unilateral Manifests as anisometropia Child may develop convergent squint in order to preferentially see clear at its far point (10-12cms) CONGENITAL MYOPIA

6. Associated with cataract, micropthalmos , aniridia , megalocornea , congenital separation of retina .

7. Developmental myopia- commonest variety School myopia (school going age 8-12 years) Etiology Axial type : physiological variation in length of eye ball precocious neurological growth during childhood Simple myopia

8. Curvatural type Underdevelopment of eye ball Role of diet in early childhood Role of genetics Prevalence in children both parents myopic(20%) One parent myopic(10%) No parent myopic(5 %)

9. Symptoms Poor vision for distance(short sightedness) Asthenopic symptoms Half shutting of eyes Clinical picture

10. 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 Diagnosis Confirmed by performing retinoscopy

11. Degenerative/ progressive myopia Rapidly progressive error which starts in childhood at 5-10 years of age High myopia in early adult life with degenerative changes Pathological myopia

12. 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

13. Role of general growth process Lengthening of the posterior segment of globe commences only during the period of active growth and ends with termination of active growth

14. Defective vision Muscae volitantes Floating black opacities in front of eyes Degenerated liquified vitreous Night blindness Symptoms

15. 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 Signs

16. 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)

17. 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

18. 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

19. Posterior staphyloma Due to ectasia of sclera at posterior pole It may be apparent as an excavation with vessels bending backward over margins

20. Degenerative changes in vitreous include: Liquefaction Vitreous opacities Posterior vitreous detachment(PVD)- Weiss’ reflex

21. Visual fields Contraction Ring scotoma may be seen ERG reveals subnormal electroretinogram due to chorioretinal atrophy

22. Retinal detachment Complicated cataract Vitreous haemorrhage Choroidal haemorrhage Strabismus fixus convergence Complications

23. Optical treatment of myopia Concave lenses Basic rule – minimum acceptance providing maximum vision Modes of prescribing concave lens- Spectacles Contact lens Treatment of mypoia

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

25. 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

26. 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

27. Disadvantages: Post operative recovery is slow Pain and discomfort Residual corneal haze in centre affecting vision E xpensive

28. Refractory surgery of choice for myopia of upto -12D Laser Assisted in-situ Keratomileusis (LASIK)

29. Patients >20 years Stable refraction for at least 12 months Motivated patient Absence of corneal pathology Absolute contraindication for LASIK Presence of ectasia Corneal thickness <450mm Patient selection criteria

30. 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

31. Epi -(E) LASIK: Only epithelial sheet is separated with Epiedge Epikeratome Devoid of complications related to corneal stromal flap

32. 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 subepithelial scarring may occur LASIK is effective in correcting myopia of -12D Advantages of LASIK

33. 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

34. Fucala’s operation Myopia of -16 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

35. 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

36. Into the peripheral cornea at approximately 2/3 rd stromal depth Flattening of central cornea, decreasing myopia Advantage: reversible procedure IntRAcorneal ring (ICR) implantation

37. A non-surgical reversible method of molding the cornea with overnight wear unique rigid gas permeable contact lenses Myopia correction upto -5D Used in patients below 18 years of age Orthokeratology

38. 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 changes Prophylaxis Genetic counselling