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refraction

1. Basics in Refraction Dr K . Sravanthy Assistant professor

2. Emmetropia is a state of refraction wherein parallel rays of light coming from infinity are focused at the sensitive layer of retina with accomodation at rest.

3. Refractive error is the second most common cause of blindness in developing countries(18%)after cataract (39%). Refractive error study in children(RESC) population based prevalence of presenting visual acuity <20/40 in both eyes in urban and rural India as 7.4% and 4.9% respectively

4. IMPORTANCE OF DOING A GOOD REFRACTION?

5. Myopia Hypermetropia Astigmatism

6. Total hypermetropia - total amount of refractive error estimated after complete cycloplegia with atropine Total hypermetropia = Latent hypermetropia +manifest hypermetropia Latent hypermetropia Manifest hypermetropia (facultative +absolute)

7. Accommodation Mechanism by which we focus diverging rays coming from a near object on to retina to see clearly Contraction of ciliary muscle – change in the shape of the lens –increases power of crystalline lens

8. Near point – nearest point at which objects can be seen clearly Far point – farthest point at which objects can be seen clearly Range of accommodation – distance between near and far point Amplitude of accommodation – difference in the dioptric power needed to focus at near and far point

9. Amplitude of accommodation (D)=100/NPA If NPA is 20 cm what is the amplitude of accommodation?

10. One eye of a child has +1.50D of latent hypermetropia and NPA of 10 cms .if he accepts a minimum plus glasses of +3 .00 D to achieve 6/6 what will be his total hyperopic error?

11. Latent =+1.5D Amplitude of accommodation is 100 /10=10 D Facultative = +10 D Absolute is +3.0 D Total = 1.5 +10+3.0=+14.5 D

12. Hypermetropia Asymptomatic Asthenopic symptoms Defective vision with asthenopic symptoms Defective vision only

13. Accommodation Can add convex power to the eye Can reduce hyperopia Can create pseudomyopia

14. Cycloplegic refraction was first put in scientific basis by Donders in 1864 Cyclo = ciliary plegia = paralysis Cycloplegic refraction procedure to determine a persons complete refractive error by temporarily paralyzing the ciliary body

15. Who requires cyclorefraction ? What drug to be used?

16. Normal child Cyclopentolate 1%+ tropicamide ( phenylephrine )0.5% Neurological issues Homatropine 2%(with tropicamide ) Atropine 1% partially accomodative esotropia Accomodative spasm – pseudomyopia Fluctuating wet retinoscopy values

17. Children – larger amplitude of accommodation Hypermetropia Accommodative esotropia Accommodative spasm Pre presbyopia LASIK

18. Which errors to ignore and which to correct?

19. - Process of emmetropization 0 to 3 yrs maximum changes - Regression of hypermetropia and astigmatism - maximum during first 18 months

20. Guidelines for refractive correction

21. For adults – give manifest correction(acceptance) Accommodative convergent squint –full correction in first sitting Accommodative convergent squint with amblyopia -full correction with patching School age (5 -15 yrs) – 2/3 rd cycloplegic correction

22. Case 1 A 3 year old child OU 6/18 CR +2DS /-0.75 DC 180 OU

23. CASE 2 6 YR old girl ,vision OU 6/18,N6 CR +4.00 DS /-1.00DC 180 OU

24. PRESCRIBE – 2/3 hyperopia +full cylinder

25. Case 3 10 year old boy Blurring of vision for distance BE 6/12 p 6/6 with -1.25 Ds

26. Pseudomyopia Cycloplegic refraction +0.5 Ds

27. Case 4 A 32 year old female comes to OPD with complaints of difficulty in seeing near On examination with +1 DS she is having N6 Distant vision was 6/6

28. Case of pre presbyopia Do cycloplegic refraction Facultative hypermetropia becoming absolute hypermetropia .

29. Case 5 8 year old difficulty in seeing blackboard since 2 months OU 6/36 ,N6 CR -2.00 Ds OU

30. Acceptance -2.00 DS OU

31. Case 6 1 and half year old Ocular examination fixation CSM BE No resistance to occlusion in BE CR - 2.00 DS /-1.00 DC 180

32. Reassure parents Wait and watch Reassess 6 monthly

33. myopia Never prescribe more minus than cycloplegic refraction Do not overcorrect Glasses given if vision is less than 6/9 or if refraction is > -1.25 Ds

34. Subjective refraction Monocular subjective refraction Binocular balancing Correction for near vision

35. Monocular subjective refraction Baseline starting point lenses Refining of sphere Refining cylindrical axis and power Finalization of sphere

36. Duochrome test Used to refine final spherical power Based on principal of chromatic aberration Emmetropes yellow light (570nm) is focussed on retina while red (620nm) is focused slightly behind , green (535nm) slightly in front of retina . both colours are equally sharp

37. Red add minus RAM Either overcorrected hyperopia or undercorrected myopia Increase minus 0.25 gradually Green add plus GAP Either undercorrected hypermetropia or overcorrected myopia Add +0.25 Ds gradually

38. Fogging To relax accommodation during refraction To keep accommodation balance in both eyes Spherical plus lenses to relax accommodation. Always put the next lens before taking a lens out to minimise accommodation If accommodation is not relaxed, pt uses accommodation which can lead to undercorrection of hypermetropia or over correction of myopia Unequal use of accommodation in both eyes can lead to asthenopic symptoms

39. Hyperopia Rays focus behind retina Accommodation is stimulated to make image clear Example in retinoscopy power is +2.50 but when you place +1.50 pt is reading 6/6 Myopia Retinoscopy power is -1.50D ,but pt can read 6/6 with – 2.50 D also

40. Jacksons cross cylinder Is a combination of two cylinders of equal strength but with opposite sign placed with their axis at right angles to each other Refinement of axis Refinement of cylindrical power

41. Refinement of axis JCC is placed with its handle parallel to axis in the trial frame

42. Refinement of cylindrical power JCC is placed with its axis parallel to the axis in trial frame

43. Thank you