MYOPIA A REFRACTIVE ERROR OF AN EYE

Short note of refractive error MYOPIA
types of myopia
defination
treatment
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1. MYOPIA BY AYUSHI R. PATEL

2. MYOPIA Shortsightedness/nearsightedness Greek word meaning:- “close the eye”.

3. Definition:- it is a type of refractive error in which parallel rays of light coming from infinity are focused infront of the retina when the accommodation being at rest.

4. AETIOLOGICAL TYPES Axial myopia:- increase in antero -posterior length of the eyeball. Curvatural myopia:- increased curvature of cornea or lens or both. Index myopia:- increased in refractive index of crystalline lens associated with nuclear sclerosis . Myopia due to excessive accommodation:- occurs in patients with spasm of accommodation. Positional myopia:- anterior placement of crystalline lens in the eyeball.

5. Clinical types Congenital myopia Simple or developmental myopia Pathological or degenerative myopia Acquired myopia

6. Congenital myopia Present since birth. Seen more frequently in children who were born prematurely or with various birth defects like marfan syndrome and homocystinuria . Usually error is about 8-10D, which mostly remains constant. Diagnosed at age 2-3 years. If unilateral,as anisometropia,may develop amblyopi strabismus. Increase in axial length and in overall globe size.

7. Associated conditions Convergent squint Cataract Microphthalmos Aniridia Megalocornea Congenital separation of retina

8. Diagnosis :- if the myopia is bilateral,the child will generally display some noticeable difficulty in seeing distance objects and will tend to hold things very close for viewing. Management:- early correction is desirable. retinoscopy under full cycloplegia . early full correction desirable prognosis.

9. Simple or developmental myopia Physiological or school myopia. Physiological error not associated with any disease of eye.

10. Aetiology Result from normal biological variation in the development of eye. Axial:- physiological variation in the length of the eyeball. Curvatural :- underdevelopment of eyeball. Role of diet in early childhood Theory of excessive near work. Role of genetic plays some role .

11. symptoms Poor vision for distance. Asthenopic symptoms:- eye straib due to dissociation between convergence and accommodation. May develop convergence weakness and exophoria and supression in one eye. Change in psychological out look. Half shutting of the eye may by complained by parents of the child .

12. signs Eyes are large and predominant. Slight deep anterior chamber. Fundus is normal : rarely temporal myopic crescent may be seen. Usually error does not exceed 6-8D. Pupil is large and react sluggishly.

13. diagnosis Confirmed by performing retinoscopy .

14. PATHOLOGICAL MYOPIA Also known as degenerative /progressive myopia. Rapidly progressive associated with degenerative changes in the eye. Which starts in childhood at 5-10 years of age and results in high myopia(7-6 D).

15. Aetiology Rapid axial growth of the eyeball outside the normal biological variations of development. Role of heredity. Role of general growth process.

16. symptoms Defective vision Night blindness Muscae volitantes /floating black opacities.

17. signs Prominent eyeballs. Large cornea. Anterior chamber is deep. Pupils are large,react sluggishly. Refractive error increases mid-30s and results in myopia of 10-20D,which may even progress to 30-40D. Visual field show contaction and in some areas ring scotoma may be seen .

18. Fundus signs A pale tessellate :-appearance due to diffuse attenuation of the retinal pigmented epithelium with visibility of large choroidal vessels.

19. Focal chorioretinal atrophy:- charactrised by visibility of larger choroidal vessels and eventually the sclera.

20. Lacquer cracks:- ruptures in the RPE bruch membrane chorioretinal complex charactrised by fine irregular yellow lines branching and criss crossing at the posterior pole.

21. CNV( choroidal neovascularization ):- which may develop in accociation with lacquer cracks and area of patchy atrophy.

22. Subretinal coin haemorrhages which may develop from lacquer cracks in the absence of cnv .

23. Foster fuchs’s pot :-is a raised,circular,pigmented lesion thant may develop after a macular haemorrhage has absorbed.

24. complications Retinal tears and retinal detachment may occur. Complicated cataract. Nuclear sclerosis. Vitreous haemorrhages . Choroidal haemorrhages and thrombosis Primary open angle glaucoma .

25. Acquired myopia Index myopia:- seen in nuclear sclerosis and incipient cataract. Diabetic myopia occurs dur to decrease in refractive index of cortex. Curvatural myopia:- Increase of corneal curvature in diseased conditions like corneal ectasias and conical cornea. Positional myopia:- Conditions producing anterior subluxation of lens .

26. Consecutive myopia:- surgical overcorrection of hypermetropia . Pseudophakia with overcorrecting IOL. Pseudomyopia :- also called artifical myopia. Produced in a conditions such as excessive accommodation and spasm of accommodation. May develop after too full a hypermetropic correction in chidren .

27. Space myopia:- experienced when the individual has no stimulation for distance fixation . Night myopia/twilight myopia:- Shift from photopic to scotopic vision at twilight Increased sensitivity to shorter wavelength of light The emmetropic eye,if accommodation for the middle range of visual spectrum will be slightly myopic for the shorter wavelengths.

28. Drug induced myopia:- Cholinergic drugs such as pilocarpine,echothiopate,di -isopropyl fluorophosphate . Sulphonamides Steroid induced myopia

29. Treatment of myopia Optical treatment:- Appropriate concave lenses(spectacles and contact lens) Minimum acceptance providing maximum vision.

30. Guidelines Low degree of myopia:- In young people:- in children above 3 years of age,myopia should be fully corrected and instructed to use their glasses constantly,for avoid developing the habit of squinting and accommodation-convergence reflex. Never overcorrect myopia. In adults people:- older than 30years patients are not able to tolerate a full correction because ciliary muscle are not accustomed to accommodate. So,prescribed less than full correction.

31. High degree of myopia Full correction can rarely be tolerated. Undercorrection as little is complicated with comfort for binocular near vision. Undercorrection to the tune of 1-3D or even more may be required. Undercorrection is always better to avoid the problem of near vision and minification of image.

32. Surgical treatment:- Radial keratotomy, photorefractive keratectomy,LASIK (laser in situ keratomileusis ) Visual hygiene:- To avoid asthenopic symptoms. Adequate illumination during close work. The clarity of the print should be good to avoid undue ocular fatigue .

33. Preventive measures Therapeutic inteventions :- atropine and pirenzepine both drugs slow downs the progression of myopia. General measures:- balanced diet in vitamins and protiens . Early management of associated debiliatating diseases. Genetic counselling :- people having pathological myopia,not to marriage with pathological myopic peoples.

34. Low vision aids Indicated in patients of progressive myopia with advanced degenerative changes. Where useful vision can’t be obtained with spectacles and contact lenses.

35. prognosis Simple myopia:- Prognosis is good. Error usually does not progress beyond 6-8D. Stabilized 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.