Techniques of refraction is the process of calculation of glass power.

Refractive errors are most common cause of ocular morbidity. It affects all age groups, and ethnic profiles. There is no g nder discrimination. Most common symptoms are blur vission along with pain in eye ,headache and tiredness. Refraction is process of determination of eye and currect it with power glass power or contact lens power. It can subjective or objective.

1. Techniques Of Refraction

2. History of refraction Definition of retinoscopy Types of retinoscopy Optics of retinoscopy Accessories needed to perform retinoscopy Objective retinoscopy Subjective retinoscopy-Duochrome test,Jackson Cross Cylinder,Astigmatic Fan Near correction Binocular balancing Optics formulae for MCQs Dynamic retinoscopy Automated refractometers Overview

3. William Bowman ( 1859) saw the linear light reflex with a Helmhotz Ophthalmoscope and used it in diagnosis of corneal disorders like keratoconus French militiary ophthalmologist Ferdinand Cuignet ( 1873 ) used the reflexes to measure the errors of refraction. M.Mehgin proved the light reflex to be a fundal reflex. H.Parent (1880 ) introduced the term retinoscopie History of retinoscopy

4. Shadow test Skiascopy Pupilloscopie Koreskopie Synonyms

5. WILLIAM BOWMAN FERDINAND CUIGNET

6. The method of estimating the refractive state of the eye is the technique of retinoscopy . Duke-Elder’s Practice Of Refraction Tenth Edition Definition

7. Accomodation Static Dynamic Types Relaxed Active

8. Illumination stage : illumination of the subject’s retina Reflex stage : reflex imagery of this area onto the observer Projection stage : projection of the image by the observer . Optics

9. Illumination stage

10. Reflex stage

11. Projection stage

12. History of the visual symptoms should be elicited Slit lamp examination should be carrried out Cover tests to determine any latent and manifest deviations should be done Visual acuity should be tested both uniocularly and binocularly and for distance and for near. Before you proceed..

13. How to proceed…

14. A dark room A retinoscope A trial set A trial frame Accessories needed

15. The trial set

16. Spherical Plano lenses Lenses in 0.25D step up to 5D Lenses in 0.5D step up from 5.5 to 10D Lenses in 1D steps from 11D to 16D High sphere power Cylindrical lenses ( by convention use negative cylindrical lenses ) Trial lenses

17. The test lenses should ideally conform to in terms of form and thickness to the spectacle lenses being prescribed. Use reduced aperture lenses(thin lenses of diameter 25mm) Preferably be planoconvex or planoconcave

18. Prisms Occluder Pin hole disc Stenopic slit Red and green filters Maddox rod

19. Comfortable , light weight Adjustable,both vertically and horizontally Fitted with at least three compartments (one for sphere,one for cylinder and the other for accessories) Compartment for cylinder should be having smooth and accurate movement Proper positioning of the dial Have the vertex distance measured. Trial frame

20. Bulb Batteries Mirror Sight hole Retinoscope

21. contd mirror Self illuminating spot streak

22. Spot retinoscopy Streak retinoscopy Easy to neutralise both meridians at the same time Neutralise one meridian at a time Uncooperative patients Needs more time Change in shape of reflex to ellipse with astigmatism Reflex is always a slit Needs skill for axis interpretation Easy axis interpretation Spot versus streak retinoscopy

23. Optics of a plane and concave mirror

24. Mirror retinoscope

25. Optics of a streak retinoscope

26. Halogen light source Battery Mirror The vergence of the light can be controlled by the sleeve by changing the distance between the lens and the light source Components of a retinoscope

27. Streak retinoscope

28. A one handed technique Manipulate the sleeve at the same time while holding the retinoscope . YOU CONTROL Holding the retinoscope STREAK AXIS VERGENCE OF STREAK

29. Changing the sleeve position-optics

30. More light enters the eye Small pupils/media opacities Remember the reflex movements are reversed in comparison with the sleeve down position Why a convergent beam

31. To find the correct position of the sleeve to get a plane mirror effect Hold the scope 33 cm from a flat surface The position of the sleeve that produces the widest beam of light Parastop Plane mirror effect

32. Distance from the retinoscope to the patient’s eye Ideal would be infinity;for practical purposes it is 6m or 20 feet Arm’s length Change the working distance in cases of very small pupils or media opacities Working distance

33. Choose a fixation target larger than 6/60 A plain spot of light can also be used Eye levels of the subject and the examiner should be same The examiner should not obstruct the patient’s view of the fixation target Stay as close to the patient’s visual axis A 10 degree off axis will produce a false astigmatic judgement of 0.5D Before you start ..

34. Ask the patient to keep both eyes open Not to look at the retinoscope light but at the fixation target Tell him he can blink as he likes! contd

35. Uniquely designed lens holder Ease of changing the lens during retinoscopy Typically, the patient sits behind the phoropter , and looks through it at the distance vision chart and then at near for individuals needing reading glasses. Phoropter

36. Sometimes a retinoscope maybe used to provide the intial setting in the phoropter . They also measure phorias , accomodative amplitudes and Vergernces .

37. Components The major components of a phoropter are JCC,prisms and lenses.

38. Refracting unit

39. Pinhole optics allow the eye to focus on smaller bundles of light entering the eye, improving focus. The stenopic slit found in all the trial sets is 1-2 mm by 15-35 mm in size. It splits an opaque disc into two halves. It is useful in finding out the axis of the cylinder. Pin hole and stenopic slit

40. Stenopic slit

41. The technique

42. Check the direction of the reflex with the direction of the movement of the retinoscope The reflex Direction Brightness Width and speed Axis Objective retinoscopy

43. With motion Against motion A neutral reflex An indeterminate reflex (scissor type/too dim) Direction of the reflex Emmetropia,hyperopia,myopia < the dioptric value of the working distance Myopia more than the dioptric value of the working distance Myopia equal to the dioptric value of the working distance

44. Is the motion of the reflex parallel to the movement of your retinoscope ? The axis of the reflex No ! Reorient

45. The relative brightness of the reflex is an indicator of the degree of ametropia Dim reflex : High refractive errors Small pupil Media opacity Brightness of the reflex

46. Increase the luminosity of the light source Dilate the pupil Reduce the working distance Sleeve up ! Dim reflex ?

47. Tells how far we are from the point of neutrality A narrower and a speedier streak indicates we are nearing neutrality At neutrality the streak widens again and speeds up more Streak width and speed

48. If the movement is “ with” add a plus lens If the movement is “against” add a minus lens If the reflex is dull to begin with start with a higher power Neutralise one meridian with spherical lenses.Then rotate 90 degress and assess the reflex. At neutralisation the patient’s far point is at the plane of the retinoscope and no movement occurs in other words the retinoscope is conjugate with the patient’s retina. To neutralise

49. To confirm neutralisation,add an extra 0.25D lens and look for reversal Move closer to the patient and a with movement should appear Contd

50. Agent Conc Maximum cycloplegia Duration of cycloplegia Mydriasis Recovery of mydriasis Tropicamide 1,2 20-25 4-6 20-30 6 hours Cyclopentolate 0.5,1 20-45 24 15-45 1 day Homatropine 2,5 30-90 72 10-30 1-3 days Scopolamine 0.25 30-60 7 days 40 3-10 days Atropine 0.25,0.5,1 120 15 days 30 7-10 days Mydriatic cycloplegic drugs

51. Video

52. Problems faced during retinoscopy

53. Mixed aberrations( irregular astigmatism,decentred lens,corneal scarring) lead to different nature of the two halves of the reflex ( one part is relatively myopic and the other hyperopic ) Find a lens that makes the two portions to meet at the centre of the pupil Scissor reflex

54. Sweep the reflex in all directions Is there a change in the speed/brightness/direction of the reflex ? Astigmatic reflex If yes then there is an astigmatism

55. Immature cataracts can lead to confusing reflexes An experienced examiner can get a rough guide as to the refractive error and give an appropritae subjective correction Confusing reflexes

56. Vision maynot be a true indication of the degree of hyperopia Do a cycloplegic refraction in hyperopia In a myope perform a dry retinoscopy as far as possible A subjective refraction after objective evaluation is the best method to prescribe in myopes Rule out pseudomyopia due to ciliary spasm Prescribe the correction as accepted under the post mydriatic test Some tips on retinoscopy ..

57. Instruction about visual hygiene When treating larger amounts of astigmatism prefer to undercorrect for the first time and gradually increase. Strive for patient comfort rather than theoretical optical correction. In irregular astigmatism a compromise should be arrived at by subjective refraction Never overplus near correction ! A short statured person may have lesser working distance ! Contd

58. Infant’s eyes are hyperopic with a very strong accomodation A nuclear cataract will have a myopic refraction with various zones of refraction while a cortical cataract will have a good central glow( do an undilated examination) Contd

59. Being stern never helps! Toys fascinate kids  Avoid using words like it doesn’t hurt Reschedule appointment if the child is hungry or sleepy .

60. Lens power formula 100 cm / focal length Lens effectivity formula D2 = d1 /1-s*d1 Spherical equivalent is sum of the (sphere + cylinder/2) Amplitude of accomodation = 100/ near point of accomodation To tranpose :add the sphere and cylinder,change the sign of the cylinder and add 90 to the axis of the cylinder Prentice rule : amount of deviation= decentration of visual axis with respect to lens center * power of lens Optics formulae

61. Infant , child Stroke patient Malingerers Mentally challenged Usefulnes of objective retinoscopy

62. Subjective retinoscopy

63. Determine the sphere Determine the cylinder- power and axis Binocular balancing

64. Determining the sphere

65. Visual acuity Spherical error Cylindrical error 6/6 - - 6/9 0.75 1.5 6/12 1 2 6/18 1.5 3 6/24 1.75 3.5 6/36 2.25 4.5 6/60 3 High Approximate error from visual acuity Cylinder error has a better acuity because there is a circle of least diffusion

66. Contd Objective refraction present Blur below 6/18 Reduce plus lenses and refine Remove the old lens only after Putting a newer lens in the hyperopic correction Control accomodation

67. DUOCHROME TEST Described by Brown and Freeman Principle : Chromatic aberration wherein green light (535nm) is focussed 0.25D in front of retina and red light ( 620 nm ) is focussed 0.25D behind it with yellow light being taken as a reference. Refinement of the sphere

68. Procedure : Determine the best sphere Do this test monocularly Ask which of the numbers or letters on the red or green appear darker,sharper and clearer.

69. Interpretation The two colours should appear equally bright If not possible to balance,then leave on the red to avoid over minusing On near addition leave it “on the green “ MORE RED-OVERPLUSSED MORE GREEN-OVERMINUSED

70. Ametropia should be corrected to 6/12 before going ahead with the test The test may over minus in elderly patients Contd

71. JACKSON CROSS CYLINDER ASTIGMATIC FAN Determinig the cylinder –Axis and Power

72. A lens with a plus cylinder at right angles to the minus cylinder mounted in a rim with a handle Available in 0.25D,0.37D,0.5D and 1 D To read it in spherocylinder form: +0.5DS/-1DC Red dots indicate minus while white dots indicate plus cylinder Axis of a cross cylinder is 45 degress to the axis of the cylinder and is in line with the handle Jackson cross cylinder

73. Establish if the eye has astigmatism Refine the cylindrical power Refine the axis Calculate the near add Contd

74. Contd

75. Axis and power determination

76. Astigmatic fan

77. The procedure

78. Astigmatic fan JCC versus Astigmatic fan Needs inactive accomodation Useful in corneal opacity

79. To measure the refractive state when the patient fixates for the near Test monocularly Aim is to use the reading addition to substitute for about one third to half of the existing amplitude of accomodation Near correction

80. The reading correction is added to the power for the distance No correction is made for the cylinder Eg : to a distance prescription of +2.5DS/-1D CY at 180 the near prescription would read + 4DS/-1DCY at 180 The near prescription

81. Do not over correct for near !

82. Simulate the patient’s habitual viewing circumstances such as lighting and working distance If tested binocularly may lead to a false low near add due to convergent accomodation Give the distance prescription and measure the amplitude of accomodation . The procedure

83. Amplitude of accomodation = 1 / near point Measure the near point by a near point ruler with a target carrier “Push up” or “push away” method NPA

84. Near point ruler

85. Age 10 20 35 45 50 55 60 65 70 Donders 14 10 5.5 3.5 2.5 1.75 1 0.5 0.25 Hofstetter 15.5 12.5 8 5 3.5 2 0.5 0.5 Accomodation with age

86. To balance the accomodation between the two eyes Assess the best corrected acuity uniocularly Binocular balancing

87. Various methods for balancing

88. Rule out Phorias Tropias Convergence insufficiency Fusional reserves Binocular vision status

89. Infrared source Fixation target Badal optometer ( position of the lens is linearly propotional to the refractive error with a constant magnification ) Autorefractor

90. Optics of AR COLLIMATION OF IR RAYS BEAM SPLITTER REMOVES REFLECTED LIGHT FROM CORNEA LATERAL MOVEMENT OF THE SYSTEM TO FIND OPTIMAL FOCUS OF SLIT ON RETINA

91. Measures at least three meridians of the eye Uses sine squared function to measure the refractive power Power = sphere + ( cylinder sine 2@ ) Contd

92. Autorefractors measure the refractive error of the patient. Not dependent on patient or operator judgement Not reliable in pathological corneas like post graft,keratoconus and post refractive surgery Pseudomyopia due to accomodation (can use cycloplegics or auto-fogging ) Anomalies in vitreous cause errors Is retinoscopy dead?

93. Patient fixates with both eyes on a near object Magnetic fixation cards incorporated in the retinoscopes A small “ with “ movement is seen for near in emmetropes with a normal accomodation Add lenses to achieve the neutral point – this represent the accomodative power Dynamic retinoscopy

94. Magnetic fixation cards

95. To check for accomodative disorders To determine the adequacy of cycloplegia Alert the practitioner to the presence of uncorrected hypermetropia or anisometropia Useful in amblyopia therapy Uses

96. Thank you …