Retinoscopy

Retinoscopy for undergraduates and post-graduates.
salient points covering examinations and PGMEE.
Detailed discussion of the technique of retinoscopy and its utility in deducing refractive errors.
Use of cycloplegic refraction and subjective refraction has been discussed.

1. Refraction and Retinoscopy Dr. Abhishek Onkar

2. Refraction is vergence (bending) of light ray when it passes from one medium to another medium of different optical density (refractive index ). Normal refraction (optical state) of the eye is essential for normal vision. Eye with normal optical state is Emmetropic and that with abnormality is Ametropic (with Refractive Error).

3. Object at infinity Parallel light rays Emmetropia : focussed on retina: no corrective lens required Myopia: focussed in front of retina: requires – ve lens for correction Hypermetropia : focussed behind retina: requires + ve lens for correction Summary of spherical refractive errors

4. In emmetropia parallel rays from infinity are focused on the retina (with accommodation at rest). This will give a clear image of object at infinity (which has sufficient size). In ametropia parallel rays from infinity are not focused on retina. So no clear image of object at infinity is formed on the retina of that eye.

5. Far point Far Point (FP) is the furthest point at which objects can be seen clearly by the eye with accommodation at rest. Position of FP depends on the optical state (static refraction) of the eye. The Far Point and the Point of Focus on the retina are Conjugate Foci. In Optics Direction of Light Ray is Reversible.

6. In emmetropia the FP is at infinity. So the rays coming from FP, and entering the eye are parallel. They are focused upon the retina to give a clear image of object at FP. In emmetropia light rays coming out from a point on the retina through the optical system of the eye will be parallel. These rays can meet only at infinity ( ie . where the Far Point is located in emmetropia ).

7. In myopia the FP is at a finite distance. So the rays coming from object at the far point, and entering the eye are divergent. These rays are focused upon the retina to give a clear image. In myopia light rays coming out from a point on the retina through the optical system of the eye will be convergent. These rays meet at the FP of the eye (at a finite distance).

8. In hypermetropia object can't be placed at the FP ( It is a virtual point behind the retina).Here the converging rays directed towards the FP behind the retina can be focused upon the retina to give a clear image by the dioptric (optical) system of the eye. In hypermetropia light rays coming out are divergent. They will only meet "beyond infinity". They can meet only at the FP of the eye, which is a virtual point behind the retina (by extrapolating the divergent rays in the reverse direction to meet behind the retina).

9. Optical state (refraction) of the eye decides the position of the FP of the eye. If the position of the FP is known the refraction can be calculated.

10. Calculating the focal point distance The method used for calculation is keeping the subject and the observer at fixed places, and bringing (shifting) the FP of the subject to the position of the nodal point of observer's eye. This is done by using converging or diverging lenses. Now we know the exact distance of the FP from patient's eye ( ie . exact distance at which we are sitting) and also the power of lens used to bring the FP to this position.( From the measurement of distance we can calculate the power required to bring the FP to this position).

11. Distance between subject and patient’s eye while performing refraction is called “ working distance.” Ideally, refraction is performed at a working distance of 1 metres . Practically, it is done at 2/3 meters (67 cm approx.). In final correction of refractive error, power equivalent to this working distance is to be subtracted from the power of lens used to bring the FP at observer’s eye.

12. For refraction at 1metre distance In emmetropia the parallel rays coming out of the subject's eye can be brought to a focus at 1 metre by using converging (convex) lens of 1 Dioptre kept close to subject's eye. In other words, if the power of the lens used to bring the FP to 1 metre is +1 D then we know that the rays coming out are parallel (which normally meet at infinity) and the eye we are examining is emmetropic .

13. In hypermetropia the diverging rays coming out of the eye are brought to a focus at 1 metre by using converging lenses of power more than +1 D.

14. In myopia of less than 1 Dioptre the converging rays coming out are focused at 1 metre by using converging lens of power less than +1 D.

15. In myopia of 1 Dioptre the rays coming out of the eye are convergent and meet at 1 metre with out using any lenses.

16. In myopia of more than 1 Dioptre the converging rays coming out of the eye will focus at the FP which is less than 1 metre from the eye. (between the patient and the observer). So this focus (FP) can be brought to 1 metre by using diverging (concave) lens.

17. When you are sitting at 1 metre from the patient, how do you know that you have brought the FP of the patient's eye (by using lenses) to the nodal point of your eye at 1 metre ? The technique of Objective method of Refraction ( Retinoscopy ) will answer these questions.

18. Retinoscopy

19. Retinoscopy Examiner determines the refractive state of the eye on the basis of the Optical Principles of refraction. Objective measurement of refractive error Starting point for subjective refraction Used to prescribe where subjective refraction can’t be performed Screening for ocular disease Keratoconus , media opacities

20. It is an objective test - it does not need any input from the patient May be the only way of determining refractive error for non-communicative or non-cooperative patients Infants/Children Non-English/Hindi speaking Learning difficulties Malingerers Low vision Laboratory animals

21. The self-illuminating Streak retinoscope Eyepiece Light source Spot or streak bulb Collar Moves up and down to change the vergence of the light Rotates to change the angle of the beam On/off/brightness control

22. Static retinoscopy To determine refractive state by patient fixating at distance so that accommodation is at rest Dynamic retinoscopy To determine refractive state by patient fixating at near, accommodation is active . Principle: Estimate the patients refractive state by bringing patient’s far point at the entrance pupil of examiner with the help of appropriate lens. The state of refraction at this particular point is called as neutralization .

23. Principle : Behaviour of the luminous reflex in the pupil of the patient is studied by moving the illumination across the fundus . This behaviour depends on the vergence of the light rays coming out of the pupil. It also depends on the position of the observer.

24. “WITH” Movement The luminous reflex in the pupil will move in the same direction of movement of the illumination across the retina ('With Movement'): When the observer is at 1 metre from the patient and the rays coming out from the patient's eye form a focus (FP of the patient): behind the observer at a finite distance (myopia< 1D) or at infinity ( emmetropia ) or 'beyond infinity' (virtual point behind patient's retina): hypermetropia

25. “AGAINST” Movement When the observer is at 1 metre from the patient and if the rays coming out from the patient's eye form a focus (FP) in front of the observer (between patient and observer- in myopia> 1D ) the luminous reflex in the pupil will move in the opposite direction of movement of the illumination across the retina ('Against Movement') .

26. When the observer is at 1 metre from the patient and if the rays coming out from the patient's eye form a focus (FP) at the nodal point of the observer then the pupil of the patient will appear uniformly illuminated. By slight tilt of illumination across retina the pupil will appear uniformly dark. This finding we get in myopia of 1D and also as the end point of retinoscopy with the observer at 1 metre from the patient.)

27. Optics of Retinoscopy Illumination stage : Light is directed into the patient’s eye to illuminate the retina . Reflex stage : A image of the illuminated retina is formed at the patient’s far point. Projection stage : The image at the far point is located by moving the illumination across the fundus and noting the behavior of the luminous reflex seen by the observer in the patient’s pupil.

28. Reflex & Projection Stages Rays coming out of Subject's Eye If the illuminated patch on Patient's retina is away from the principal axis, the rays coming out will not enter Observer's eye. When the illumination is moved across the fundus towards the principal axis the rays coming out enters observer's eye.

29. The first ray of light entering observer's eye is from the same edge of the pupil as the first position of retinal illumination. As the illumination on the retina moves towards the principal axis the light reflex in the pupil also moves in the same direction. The last ray of light entering the observer's eye is from the other edge of the pupil. This gives a with movement reflex in the pupil .

30. The first ray of light entering observer's eye is from the opposite edge of the pupil when the position of the retinal illumination is considered. (Light rays cross at FP and the diverging rays are entering observer's eye). As the retinal illumination moves towards the principal axis the light reflex in the pupil moves in the opposite direction. The last ray of light entering the observer's eye is from the other edge of the pupil. This gives an against movement reflex in the pupil. (seen in myopia more than 1D)

31. As the retinal illumination moves towards the principal axis, the rays coming out will focus on the nodal point of observer's eye. This makes the pupil of the patient uniformly illuminated. (The rays coming out through all the parts of the pupil are focused at the nodal point of observer's eye). By a slight shift of retinal illumination this focal point is displaced away from observer's eye making patient's pupil uniformly dark. This finding is observed as end point of retinoscopy and in eyes with 1 D myopia( retinoscopy done at 1 metres ).

32. Illumination Stage Light rays entering subject's eye. Consider only the immediate source of illumination in front of the subject's eye . This may be a virtual image or real image of an original source of illumination behind the subject. When the immediate source is towards one side, the other side of the retina will be illuminated. When the source is shifted to the other side, illumination will be shifted to the opposite side of the retina. This will be the situation in all states of refraction of the eye.

33. If we are using a Plane mirror, the virtual image of the original source of illumination is formed as far behind the mirror as the original source is in front of it. So, the tilt of the mirror to one side will shift the image (immediate source of illumination) to the other side. Tilt of the plane mirror and the shift of illuminated patch on the retina are in the same direction.

34. If we are using a Concave mirror, the real image of the original source of illumination is formed in front of the mirror ( position depends on the focal length of the mirror). So, the tilt of the mirror to one side will shift the image (immediate source of illumination) to the same side itself. Tilt of the concave mirror and the shift of illuminated patch on the retina are in opposite directions.

35. In Practice we are considering the movement of the mirror. When we use plane mirror we get movement of the mirror and movement of the retinal illumination in the same direction.( because of the movement of immediate source of illumination – ie virtual image formed behind the mirror –is in the opposite direction of movement of the mirror). When we use concave mirror we get movement of the mirror and movement of retinal illumination in opposite directions (because of the movement of immediate source of illumination - ie real image formed in front of the mirror – in the same direction of movement of the mirror). Movement of reflex is decided by the movement of immediate source of illumination and the refractive state of the eye. Movement of immediate source of illumination is decided by the type of mirror used.

36. Identifying end point 1. Intensity In high refractive errors we get a faint reflex and in low refractive errors we get a brighter reflex. 2. Speed In high refractive error we get a slow movement, and in low refractive error a rapid movement of the reflex. As the neutral point is reached the movement of the reflex is fast. 3. Size In high refractive error we get a narrow reflex. Reflex will fill the pupil when the neutral point is reached.

37. To refine result – If your assessment is correct you will get the following results-- After reaching the neutral point (end point) in Retinoscopy (with plane mirror) moving slightly towards the subject will give a ‘with movement’ (because the Far Point is now behind the Observer). Moving slightly away from the subject will get an ‘against movement’ (because now the Far Point is between the observer and the subject).

38. Recording of retinoscopy results- the Cross diagram

39. Determining axes of astigmatism

40. Principle of cycloplegic refraction Determination of total refractive error during temporary paralysis of cilliary muscles as an instillation of cycloplegic drugs which otherwise doesn’t manifest on subjective non-cycloplegic refraction Total Hyperopia Latent hyperopia Manifest hyperopia facultative hyperopia Absolute hyperopia

41. Indication for cycloplegic refraction Accommodative esotropia All children younger than 3 yrs Suspected latent hyperopia Suspected pseudomyopia Uncooperative/noncommunicative patients Variable and inconsistent end point of refraction

42. Indication for cycloplegic refraction Visual acuity not corrected to a predicted level Strabismic children Amblyopic children Suspected malingering and hysterical patients

43. Gauri S Shrestha, M.Optom, FIACLE Selection and use of specific cycloplegic agents Variable degree of pupil dilatation and cycloplegia Instill cycloplegic alone or with mydriatrics Agent [C%] Dosage Max cyclople Duration of effect Residual accom Atropine sulfate 1, 2 1D TID 3 days 3-6 hrs 10-18 days Ngble Sco-mine HBR 0.25% 1D TID 60 mins 5-7 days ngble Cyclo-late HCL 0.5, 1 , 2 1D TID 30-45 mins 24 hrs minimal Tro-mide HCL 0.5, 1 1D TID 20-30 mins 4-8 hrs moderate

44. Indication of Cycloplegic refraction All hyperopes . One who complains of Asthenopic symptoms. Who come for glass for first time Accommodation is abnormally active.

45. When cycloplegics are used, a correction must be made to compensate for the normal tone of ciliary muscles. When atropine is used, 1 D is deducted in final correction. When other cycloplegics are used, 0.5 D is deducted in final correction.

46. Examples +4.0DS +4.0DS +4.0DS +4.0DS For retinoscopy done at 1m ( without any cycloplegic ), final correction would be = +3.0 DS Both eyes For retinoscopy done at 2/3m ( without any cycloplegic ), final correction would be = +2.5 DS Both eyes If atropine had been used for cycloplegia (D=1m), final correction would be= 2.0DS BE

47. +5.0DS +5.0DS +4.0DS +4.0DS For retinoscopy done at 1m ( without any cycloplegic ), final correction would be = +3.0 DS, +1.0 DC @ 180° Both eyes

48. Principle of subjective refraction Subjective determination of the combination of sphere and cylindrical lenses that artificially places the far point of Each Eye of patient at infinity This is the combination of lenses that provides best VA with accommodation relaxed To find the strongest plus lens or the weakest minus lens which allows the patient to obtain the best possible visual acuity

49. When to start subjective refraction? After objective retinoscopy/Auto refraction Accurate refining when objective retinoscopy is inaccurate Media opacities, keratoconus, oblique and irregular astigmatism Post mydriatic cycloplegic refraction When retinoscope or auto-refractor is absent

50. Subjective refraction techniques Fogging Stenopaic slit Jackson’s cross- cylinder

51. Subjective refraction techniques Astigmatic fan/ Clock dial/ Sunburst dial Phoropter