Subjective Refraction in details with each steps

About Subjective Refraction

1. SUBJECTIVE REFRACTION Presentor : Sushila Oli BOVS,2 nd year NAMS,LEIRC Moderator: Dikshya Khadka

2. Contents Introduction Principle Monocular Subjective Refraction Monocular Best Sphere Refinement and Finalization of Cylindrical lens Axis and Power Binocular Balancing

3. Clinical Refraction The procedure of determining and correcting the refractive status of the eye is known as clinical refraction. The clinical refraction comprises two complementary methods: Objective refraction Subjective refraction

4. Objective Refraction The examiner determines the type and degree of refractive error on the basis of optical principles of refraction without active participation of the patient. Common method of Objective refraction are: Retinoscopy Keratometry Autorefraction Photorefraction

5. Subjective Refraction Subjective refraction is the method of determining the most suitable lens to be prescribed, with the proper response of patient. It is the technique of comparing one lens against another, using changes in vision as the criterion, to arrive the dioptric lens combination that results in maximum visual acuity.(polasky 1991) The purpose is to find the strongest plus lens or the smallest minus lens which allows the patient to obtain the best possible visual acuity.

6. Principles of Refraction Subjective determination of the combination of sphere and cylindrical lens that artificially places the far point of each eye of patient at infinity. This is the combination of lenses that provides best VA with accomodation relaxed.

7. Monocular subjective refraction : Performed with contralateral eye (not being tested) under occlusion. Binocular subjective refraction : Performed with both eyes viewing a single target while one of the eyes tested. Types

8. MONOCULAR SUBJECTIVE REFRACTION Steps:- Starting point Control of accommodation Monocular best sphere Refinement and finalization of cylindrical Lens Axis and Power 5)Monocular spherical end point

9. Starting Point The refractive errors is determined by objectives techniques and acts as a starting point from which the subjective refraction can take place. Alternatively, the habitual spectacle correction or results of previous subjective refraction may suffice as the starting point.

10. Things to remember while doing subjective refraction The geometric centers of the lens must be aligned with the centers of entrance pupils of the patient's eye. Adjustments of IPD. Appropriate vertex distance. Appropriate pantoscopic angle.

11. 2. Control of Accommodation An initial objective is maintaining accomodation in relaxed state because fluctuating accomodation may confuse retinal focus presented by each change of lens combinations before eyes. Two classic means of keeping accommodation at rest are: Cycloplegia Fogging

12. Cycloplegia Cycloplegia causes paralysis of accommodation. Advantageous in case of accommodative spasm, latent hyperopic, convergent strabismus due to over accommodation. These conditions tend to resist routine technique for accommodative relaxation. However, cycloplegia also inhibits normal ciliary  tonus. So, subjective refraction is done by reducing that amount of ciliary tonus.

13. Fogging Accommodation activity is best controlled by placing the focus of distant target in front of retina i.e. making the eye artificially myopic-fogging technique. Activation of accommodative system moving the focus forward and farther from retina that deteriorates vision. Optimal vision is only attainable by moving the focus towards the retina by interchanging of lenses while accommodation remains inactive – Unfogging.

14. For hypermetropes/compound hyperopic astigmatism: Add sufficient plus to ensure that both primary meridians are focused in front of retina. For myopes/compound myopic astigmatism : Both meridians are already in front of retina. High myopes; minus lenses may be added, but weaker than that of any meridian. For mixed astigmatism : Plus lens of sufficient strength to place hyperopic meridian in front of retina.

15. Classic fogging technique Fogging technique is applied to uncorrected eye. Initial objective is to blur the eye by sufficient plus(or reduce minus) to reduce visual acuity to snellen 20/100(6/30) or worse. Reduce plus power(or add minus) in 0.25D steps until VA is improved to point that patient can distinguish lines in chart at distance for a astigmatic correction (unfogging).

16. 3. Monocular best sphere A patient without astigmatism should be fully corrected by this step alone. However, if astigmatism is present, the aim of this step is to position the two focal lines at retina. Methods : Duochrome method

17. Bichrome or Duochrome test:- Based on chromatic aberration. Duochrome chart is a distance VA chart with black letters, split equally into two equal halves. Letters on one half on red background and others on green background. This test is performed monocularly, and is used to refine the spherical component.

18. Since the red and green foci are nearly equally spaced about yellow, an emmetrope should see black objects on the two backgrounds equally clear. In myopes red are clearer. In hypermetropes, letters on green are clearer. The examiner ask the patient “Do the Black letters stand out more on the red or green background? Or do they appear equal?”

19. When patient tells red letters slightly more clear than green; patient is myopic or under corrected myope . Neutrality is achieved when the patient subjectively reports that the letters on both backgrounds appear equally as prominent.

20. Cont… REFRACTIVE STATE COLOUR SEEN E mmetrop e Red = Green Corrected myope Red(slightly clear) Undercorrected myope Red Over-corrected myope Green Corrected hypermetropia Red =Green Undercorrected hypermetropia Green Overcorrected hypermetropia Red

21. Refinement and finalization of cylindrical lens axis and power Jackson’s cross cylinder technique Stenopaeic slit Clock dial and fogging technique Astigmatic fan dial test / sun burst

22. Jackson’s Cross Cylinder The 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 and mounted in a handle.

23. PRINCIPLE JCC is a spherocylindrical lens having a spherical component which is twice the power of sphere and of opposite sign. Eg: +0.25DS combined with -0.50DC. This result in net power of +0.25DC in one axis and -0.25DC in other axis. The spherical equivalent of JCC is 0.

24. Marking of JCC The principal meridian are marked in the periphery of JCC. Lens mounted on a handle which is placed 45degree to the axis of cylinder. Red mark =minus meridian Black mark=plus meridian

25. Handle of JCC A handle attach between the two marked axes, which enables the lens to be “twirled” before the eye by rotation of handle. In this manner, the position of minus and plus axes are interchanged rapidly and alternately. JCC is often term as flip-cross cylinder.

26. Starting point of JCC After retinoscopy , adjust the sphere. End point of spherical adjustment is the starting point of JCC refinement. Circle of least confusion must be on retina(ILM), so check sphere first.

27. Discovery of Astigmatism Place the JCC at 90° and 180° and flip infront of eye to detect whether astigmatism is present or not. If patient see any change in visual acuity in either of position then astigmatism is present. If no change in visual acuity is detected at either of position then place JCC at 45° and 135° to confirm astigmatism present or not .

28. If Astigmatism is present Refinement of Axis Refinement of Power Reason: The correct axis can be found in the presence of an incorrect power and the full correct power cannot be found in an incorrect axis.

29. Refinement of Axis Put the cylindrical lens(discovered during retinoscopy) in the trial frame. Occlude one eye and ask him to see on the Snellen’s chart. Hold the JCC with the handle parallel to axis of cylindrical lens in the frame. The axis of the JCC (white and red marking) will be at 45° to the axis of the cylinder in trial frame. Flip the JCC so that the position of red and white marking is reversed.

30. 5. Ask the patient to tell about any change in visual acuity. 6. If the patient notice no difference between the two position, the axis of the correcting cylinder in the trail frame is correct . 7. If visual improvement is attained in one of the positions .

31. 8. “Minus” correcting cylinder should be rotated in the direction of the minus cylinder component (red)of the cross cylinder. 9. “Plus” correcting cylinder should be rotated in the direction of the plus cylinder component (white) of the cross cylinder. 10. Repeat test till neutral point is reached.

32. Refinement of Power Optical principle of power refinement While determing the power, JCC will either increase or decrease residual cyl, either expanding or collapsing the astigmatic interval and circle of least confusion. Thereby making the target less or more clear. If “circle of least confusion” at retina, increase in size results in longer interval of strums and “That’s look awful” and if decrease in size results in shorter interval of strums and “That is much better”.

33. Put the cylindrical lens (discovered during retinoscopy) in the trial frame. Occlude one and ask the patient to look at clear line on Snellen chart. JCC is placed with its axis parallel to the axis of the cylinder in the trail frame. The axis of the JCC(white and red marking) will be at the axis of the cylinder in the trail frame. Flip the JCC so that the position of the red and white marking is reversed. Refinement of Power

34. Cont… 5. Ask the patient to tell about any change in visual acuity. 6. If the patient notices no difference between the two positions, the power of the correcting cylinder in the trail frame is correct. 7. If visual improvement is attained in one of the positions. 8. A corresponding corrections should be made. 9. Verified till final correction is attained.

35. Cont... Examples Retinoscopy: -1.00DS / -0.75DC *120 ° If the patient prefers the lens When red marks are aligned with trial cyl axis(120 ° ), add -0.50 DC When white marks are aligned with trail cyl axis (120 ° ),reduce -0.50DC Equally clear : you have the right power

36. Cont ... For each -0.50DC changes, you need to add +0.25DS, to keep the circle of least confusion on the retina. Add - 0.25DS for each +0.50DC change So in example: -1.00DS/-0.75DC*120 ° If the patient prefers red marks Final power is : -0.75/-1.25DC*120 °

37. Stenopaeic slit Stenopaeic slit is a black disk with aperture ranging from 0.5 to 1.0mm in width and up to 15 mm in length. This is used to check the principal axis of astigmatism when there will be no clear view due to media opacity . Width of slit approximates to that of a pin hole- assumed to limit light to one meridian

38. Procedure Occlude one eye. Put the stenopaeic slit in the trail frame at 90° or 180°and note vision improves or not. If vision does not improve , rotate the slit till the vision is sharpest at a point. After finding the axis of cylinder power. Add spherical power using stenopaeic slit till best VA is reached.

39. Clock dial and fogging technique Obtain best VA by best sphere method and fog the eye at VA up to 6/12 by adding enough plus lens . Ask the patient which of the lines are sharpest or most distinct? To determine the axis of correct cylinder, the smaller of two numbers reported by patients multiplied by 30 deg.

40. For example, if patient reports 12 to 6 o’clock l ine are most distinct ; then axis is 180 deg and add minus cylinder perpendicular to the darkest line( i.e 180 deg) till all lines are equally clear. If the lines are darker but the vision is not so clear then reduce the plus sphere until the patient achieve maximum vision for distance .

41. Astigmatic fan dial test/ sun burst Consists of dial of lines radiating at 10 deg. interval to one another Patient is asked to see fan after fogging by +0.50 D P atient without astigmatism will see all lines equally clear

42. Cont.. In astigmatism, one or more line will be seen more sharply defined . The concave cylinder is then added with its axis at 90 deg to the clearest line until all the lines are equally clear.

43. Binocular balancing This is the final steps in subjective refraction also known as equalization of vision or accommodative effort which allows both the retinal imag es simultaneously in focus . If the corrected VA is same in both eye, the balancing procedure may consists of comparision of the VA for the two eyes. If the corrected VA is not same in both eyes, then a method not based on VA must be used.

44. Unequal accommodation response between the two eyes Inequality in the clarity or size of the retinal images Reduce stereo acuity or fusional amplitudes Discomfort and visual inefficiency

45. Common techniques of spherical equalization are: 1. Alternate occlusion method 2. Prism dissociation method

46. Alternate occlusion > Both eyes are alternately occluded repeatedly while patient views VA chart at distance through the spherocylindrical correction determined monocularly Performed with handheld cover paddle. Patient compares and informs which eye resolves more letters on chart. The examiner then adjusts the spherical balance so as to produce equality between the eyes.

47. Not helpful in aniso-oxyopia and amblyopia Subject compares a visible object with a previous one remembered but no longer visible. Must be repetitive and slow enough for patient to recognize and accurately state the eye with clearer vision Also be fast enough so that patient cannot accommodate for residually hyperopic eye while the other is occluded

48. Prism dissociation Placing 3A of base-down prism in front of the right eye and 3 of base- up prism in front of the left eye. The charts gets separated vertically, the upper chart being seen by the RE and lower by the LE Patient is asked to report whether the letters are more distinct or easier to read in the upper chart or lower chart. If the two 20/25 lines are equally distinct for the two eyes, the accommodative state of the two eyes is considered to be balanced.

49. If the patient reports a difference in clarity of the letters for the two eyes. +0.25 D is added in front of the eye with the better vision and the test is repeated. Once the patients VA is balanced at 20/25, the patient is defogged binocularly to the criterion. Endpoint-balance at equality of acuity. When end point of balance is reached, remove prism and find binocular spherical end point.

50. Methods of binocular balancing A) Fogging and alternate occlusion : In this method both the eyes equally fogged by + 1.0DS lens and cover test is performed to know the balancing . If both the eyes have equal blur the power are balanced, if one eye is clear than other the +0.25 DS is added in the eye having clear image until both eyes have equal blur then reduced the power till the patient achieve 6/6 vision in both the eyes.

51. Cont... B) Duochrome test with fogging : Both the eyes are fogged by +1.0 DS lens and duochrome test is applied . C) Prism Dissociation Test : Both the eyes are fogged with +1.0 DS lens then 3 or 4PD base down prism is place in RE and 3 or 4 PD base up prism is placed in LE with 6/12 line in snellenschart , if patient see single line binocularly then power is correct, if see two line with difference in clarity then +0.25 DS is added in the eye with clear image until two lines are equally distinct .

52. Cont ... D) Turville infinity balance Technique : A set of letters is seen with a septum in the middle which mask some letters from each eye. If all letters are seen clearly and equally then there is binocular balance E) Polaroid filters

53. Reference Theory and optics of Refraction Primary Care Optometry Borish’s Clinical Refraction https://www.ophthalmictechnician.org/index.php/tech-tips/160-to-fog-or-not-to-fog

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