myopia

post grad myopia lecture

1. MYOPIA

2. SOURCES 2 Theory and practice of optics and refraction by AK Khurana Borish’s clinical refraction Strabismus simplified,Pradeep Sharma Parsons’ Diseases of the Eye - 22 nd Edition, 2015

3. OUTLINE Optics of myopia Classification Treatment of myopia Complications Prognosis

4. MYOPIA Derived from two Greek root words ( Greek: μυωπία, muōpia , from myein "to shut" - ops (gen. opos ) "eye“ ) Myopia or shortsightedness is a type of refractive error in which parallel rays of light coming from infinity are focused in front of retina when the accommodation is at rest

5. Image formation In myopia image formed in front of retina 5

6. 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 6

7. Optics of myopia Nodal point is further away from retina Accommodation in uncorrected myopes is not developed normally, they may suffer from convergence insufficiency, exophoria,and early presbyopia

8. TYPES OF MYOPIA 8 Etiologically Axial myopia :result from increase in anterioposterior length of eyeball Curvatural myopia :occurs due to increased curvature of cornea or lens or both Index myopia :increase in refractive index of crystalline lens associated with nuclear sclerosis M yopia due to excessive accommodation :occurs in patients with spasm of accommodation Positional myopia

9. TYPES OF MYOPIA Clinically, congenital myopia simple or developmental myopia pathological or degenerative myopia acquired myopia 9

10. TYPES OF MYOPIA According to degree: Classically : Very low : upto – 1.00D Low : –(1.00-3.00)D Medium : –(3.00-6.00)D High : –(6.00-10.00)D Very high : above –10.00D

11. Congenital myopia Seen more frequently in children who were born prematurely or with various birth defects Usually error is about 8-10D, which mostly remains constant Most of the times the error manifests as anisometropia May sometimes be associated with other congenital anomalies such as cataract, microphthalmos , aniridia , megalocornea 11

12. Congenital myopia Early correction is desirable to help the children to develop normal distance vision Full cycloplegic refractive error including any astigmatic correction should be prescribed 12

13. Guidelines for refractive correction in young infants and children Myopia Age <1 yr : -4.00 or more Age 1-2yr: -3.00 or more Age2-3yrs: -3.00 or more

14. Simple myopia Also known as physiological or school myopia Physiological error not associated with any disease of eye Etiology: result from normal biological variation in the development of eye 14

15. Simple myopia Aetiology Axial Physiological variation in the length of the eyeball Curvatural Underdevelopment of eyeball. -------- Role of diet in early childhood. -------- Theory of excessive near work. 15

16. Simple myopia Symptoms : . Poor vision for distance Asthenopic symptoms eye strain due to dissociation between convergence and accommodation M ay develop convergence weakness and exophoria and supression in one eye. Change in psychological outlook 16

17. Degree of myopia Visual acuity -0.50 6/9-6/12 -1.00 6/18 -1.50 6/24 -2.00 6/36 -3.00 6/60 -4.00 4/60 -5.00 3/60 -6.00 2/60 17 Degree of myopia Rough estimate of visual acuity

18. Simple myopia: SIGNS Eyes are large and prominent Slight deep anterior chamber Fundus is normal;rarely temporal myopic crescents may be seen Usually error does not exceed 6-8D 18

19. Simple myopia :diagnosis Confirmed by performing retinoscopy 19

20. Pathological myopia Rapidly progressive error resulting in high myopia usually apparent during 1 st decade of life Etiology: 1)Heredity 2)General growth process 20

21. Pathological myopia High myopia is considered to be sex linked recessive inherited disorder It is said that increased axial length, degenerative changes in retina and vitreous, and pathological complications are determined by different genes. Inheritance can be AD, AR ,X-LINKED 21

22. 22 Genetic factors General growth (play major role) ↓ More growth of retina ↓ Stretching of sclera ↓ Increased axial length ↓ Degeneration of choroid ↓ Degeneration of retina ↓ Degeneration of vitreous Features of pathological myopia etiological hypothesis for pathological myopia (Plays minor role) Elongation of the eyeball posterior to equator in pathological myopia.

23. Pathological myopia 23 Symptoms defective vision muscae volitantes night blindness

24. Pathological myopia Signs: Eyes are prominent, appearing elongated, and even stimulating an exophthalmos Cornea is large and anterior chamber is deep Pupils are larger Refractive error: increase by as much as 4D yearly stabilizes at about the age of 20 but occasionally may progress until mid 30s frequently result in myopia of 10-20D 24

25. 25 Retinal changes in pathological myopia Optic disc: appears large and pale at temporal edge a characteristic myopic crescent present Degenerative changes: in retina and choroid are common. occurs tigroid appearance of fundus due to diffuse attenuation of the RPE with visibility of large choroidal vessels

26. Retinal changes in pathological myopia Foster- Fuchs spot may be present at macula Cystoid degeneration may be seen at the periphery In advanced cases there occurs Focal chorio -retinal atrophy which is characterized by visibility of the larger choroidal vessels and eventually the sclera, total retinal atrophy, particularly at central area 27

27. Retinal changes in pathological myopia There may be associated lattice degeneration and or snail track lesions Retinal tears, haemorrhage , retinal detachment may be seen A posterior staphyloma due to ectasia or bulging of sclera at posterior pole due to focal expansion and thinning .

28. Retinal changes in pathological myopia It occurs in about a third of eyes with pathological myopia, and is virtually always peripapillary or involves the macula.Staphyloma development can be associated with macular hole formation Degenerative changes of vitreous include: liquefaction, vitreous opacities, PVD Visual field shows contraction and sometimes ring scotoma may be seen. 29

29. 30 Fundus changes in myopia Foster- Fuch’s spot Peripapilary and macular degeneration

30. 31 Choroidal neovascularization associated with a lacquer crack and high myopia. Peripheral retinal degernerations : A:Lattice degeneration, B:Snail track degeneration C:Acquired retinoschisis D:white-with-pressure E:Focal pigment clumps F:Diffuse chorioretinal degeneration G:Peripheral cystoid degeneration

31. 32 Pathological myopia :complications Rhegmatogenous retinal detachment (RD) Foveal retinoschisis and macular retinal detachment without macular hole formation may occur in highly myopic eyes with posterior staphyloma , probably as a result of vitreous traction

32. Pathological myopia :complications Complicated cataract which may be either posterior subcapsular or early onset nuclear sclerotic Nuclear sclerosis Vitreous haemorrhage Choroidal haemorrhage and thrombosis

33. 34 High myopia can be seen in these syndromes • Down syndrome • Stickler syndrome • Marfan’s syndrome • Prematurity • Noonan syndrome • Ehlers– Danlos syndrome • Pierre–Robin syndrome

34. 35 Acquired myopia Causes: Index myopia : nuclear sclerosis incipient cataract . C urvatural myopia increase of corneal curvature in diseased conditions like corneal ectasias , and conical cornea P ositional myopia

35. 36 Acquired myopia consecutive myopia surgical overcorrection of hypermetropia pseudophakia with overcorrecting IOL. Pseudomyopia Space myopia –Experienced when the individual has no stimulation for distance fixation It is never more than 0.75-1.5D

36. Acquired myopia Night myopia or twilight myopia 37

37. 38 Acquired myopia D rug induced myopia -Cholinergic -Steroid induced - Sulphonamides

38. TREATMENT OF MYOPIA 39 Optical treatment Surgical treatment General measures Visual hygiene Low-vision aids

39. Optical treatment 40 Guidelines for correcting low degree of myopia upto -6D Children younger than 8yr should be fully corrected and instructed to use their glasses constantly Adult younger than 30 yrs: usually accept their full correction. Older than 30 yrs: not able to tolerate a full correction over 3D if they have never worn glasses before. prescribe less than full correction with which the patient has comfortable.

40. Optical treatment 41 Include prescription of appropriate concave lens minimum acceptance providing maximum vision should be prescribed . never overcorrect myopia

41. Optical treatment 42 guidelines for correcting high myopia full correction can rarely be tolerated under correct as little is compatible with comfort for binocular near vision under correction to the tune of 1-3D or even more may be required under correction is always better to avoid the problem of near vision and minification of image.

42. 43 Modes of prescribing concave lenses Spectacles Contact lenses

43. Surgical treatment: 44 Radial keratotomy Making deep (90 percent thickness radial incision in the peripheral cornea leaving about 4mm central optical zone. On healing flattens central cornea there by reducing refractive power|(refractive error between -1.5to -6D.

44. Photorefractive keratectom y Photorefractive keratectomy Photoablation of excimer LASER Which can accurately ablate corneal tissue to an exact depth with minimal distortion of normal tissues Myopia is treated by ablating the central anterior corneal surface so that it becomes flatter Approximately 10 micron of ablation corrects 1D of myopia.

45. 46 LASIK Laser in situ keratomileusis Currently most frequent performed refractive procedure Can correct myopia upto -10D Automated microkeratome is used to raise corneal flap Excimer laser applied to stromal bed and flap again repositioned

46. General measures: 47 Balanced diet rich in vitamins and proteins Early management of associated debilitating diseases

47. Visual hygiene : 48 to avoid asthenopic symptoms adequate illumination during close work clarity of print should be good to avoid undue ocular fatigue

48. Low vision aids: 49 Indicated in patients of progressive myopia with advanced degenerative changes where useful vision cannot be obtained with spectacles and contact lenses

49. Prophylaxis 50 genetic counseling for people having pathological myopia, not to marry pathological myopic peoples

50. PROGNOSIS 51 Simple myopia Prognosis is good. Error usually does not progress beyond 6-8D Stabilizes by the age of 21 Pathological myopia: Visual prognosis is always guarded Possibility of progressive visual loss due to degenerative changes and danger of complications such as retinal detachment should be borne in mind.

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