MYOPIA Simple myopia upto 5D Developmental myopia –10D at birth Pathological axial myopia: starts at 5-10 yr of age and gors on increasing till 25 . May achieve 15- 25D or more. Pathological curvature myopia. K.conus Index myopia i.e. nuclear sclerosis, DM, drugs: Hydralazine, chlorthalidone and phenothiazines.
CHANGES IN MYOPIA Axial myopia affects post. half more oftenly and adversely as compared to ant half. Post staphyloma Myopic crescent Peripheral retinal degenerations leading to thinning, hole formation and ret. detach. Mac. Hole. Vitreous degeneration: Choroidoretinal atrophy, laquer’s crackes, ch small vessel haemorrhages and thrombises leading to Foster-Fuchs spot.
CHANGES IN MYOPIA--- CONTINUED---Eyes look prominent, AC deep and pupils wide.Pseudoesotropia. Poor visual acuity in spite of optical correction.Centra/peripheral scotomas.Pre-senile cataract, increased prevalence of POAG, PDS/PDG,steroid responsiveness.Marfan’s, Stickler, Ehlers-Danlos and Pierre- Robin----Syndromes.
SYMPTOMS Indistinct distant vision. Disproportionate accommodation and convergence may lead to discomfort in near work.(High myopia) Black spots and flashes in front of eye.
RADIAL KERATOTOMY PROCEDURE: Multiple deep stromal radial cuts starting from optical zone (Central 4mm) up to limbus by diamond knife. Causes bulging of peripheral cornea and flattening of the central. INDICATIONS: Static myopia upto 5D of adults with no or little astigmatism. CONTRA-INDICATIONS: Before 21 year of age, significant astigmatism and corneal opacity.
RADIAL KERATOTOMY cont.. SUCCESS RATE: 50% stable by about six month. PER-OPERATIVE COMPLICATIONS: Accidental perforation, involvement of visual axis and incisions of wrong direction. POST -OPERATIVE COMPLICATIONS: Bacterial keratitis, endophthalmitis, introstromal inclusionst, globe rapture and cataract formation.
PHOTOREFRACTIVE KERATECTOMY PROCEDURE: Optical zone anterior stromal ablation by Excimer Laser after de- epithelial removal. This thins central cornea and reduces is by diaptoric power. INDICATIONS: Static myopia upto 6D , astigmatism upto 3D. CONTRA-INDICATIONS: High astigmatism and myopia more than 7D.
PHOTOREFRACTIVE KERATECTOMY cont.. SUCCESS RATE: 90% achieve final refractive error of 1D. Long term drift especially in high myope. COMPLICATIONS: Mild pain and watering for few days. Corneal scarring 3% of cases. Night glare.
LASER IN-SITU KERATOMILEUSIS PROCEDURE: Same as PRK except that laser is applied after a hinged corneal flap by micro keratome. INDICATIONS: S myopia upto 12D , astigmatism upto 5D. CONTRA-INDICATIONS: Eyes with thin cornea.
LASER IN-SITU KERATOMILEUSIS cont.. SUCCESS RATE: Results are better than PRK. COMPLICATIONS: Buttonholing, amputation, incomplete irregular flaps and corneal perforation. Wrinkling, distortion or dislocation of flap. Epithelial in growth under flap. Keratitis, anterior segment ischaemia and optic neuropathy.