Techniques of refraction is the process of calculation of glass power.
- 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
- 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
- 6. The method of estimating the refractive state of the eye is the technique of retinoscopy . Duke-Elder’s Practice Of Refraction Tenth Edition
- 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 .
- 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.
- 14. A dark room A retinoscope A trial set A trial frame
- 16. Spherical 1. Plano lenses 2. Lenses in 0.25D step up to 5D 3. Lenses in 0.5D step up from 5.5 to 10D 4. Lenses in 1D steps from 11D to 16D 5. High sphere power Cylindrical lenses ( by convention use negative cylindrical 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.
- 20. Bulb Batteries Mirror Sight hole
- 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
- 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
- 28. A one handed technique Manipulate the sleeve at the same time while holding the retinoscope. YOU CONTROL STREAK AXIS VERGENCE OF STREAK
- 31. More light enters the eye Small pupils/media opacities Remember the reflex movements are reversed in comparison with the sleeve down position
- 32. 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
- 33. 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
- 34. 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
- 35. 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!
- 36. 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.
- 37. Sometimes a retinoscope maybe used to provide the intial setting in the phoropter . They also measure phorias, accomodative amplitudes and Vergernces.
- 38. The major components of a phoropter are JCC,prisms and lenses.
- 40. 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.
- 41. Stenopic slit
- 43. Check the direction of the reflex with the direction of the movement of the retinoscope The reflex Direction Brightness Width and speed Axis
- 44. With motion Against motion A neutral reflex An indeterminate reflex (scissor type/too dim) 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
- 46. Is the motion of the reflex parallel to the movement of your retinoscope? No ! Reorient
- 47. The relative brightness of the reflex is an indicator of the degree of ametropia Dim reflex : High refractive errors Small pupil Media opacity
- 48. Increase the luminosity of the light source Dilate the pupil Reduce the working distance Sleeve up !
- 49. 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
- 50. 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.
- 51. To confirm neutralisation,add an extra 0.25D lens and look for reversal Move closer to the patient and a with movement should appear
- 52. Agent Conc Maximu m cyclople gia Duration of cyclople gia Mydriasi s Recovery of mydriasis Tropicam ide 1,2 20-25 4-6 20-30 6 hours Cyclopen tolate 0.5,1 20-45 24 15-45 1 day Homatro pine 2,5 30-90 72 10-30 1-3 days Scopola mine 0.25 30-60 7 days 40 3-10 days Atropine 0.25,0.5, 1 120 15 days 30 7-10 days
- 55. 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
- 56. Sweep the reflex in all directions Is there a change in the speed/brightness/direction of the reflex ? If yes then there is an astigmatism
- 57. 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
- 58. 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
- 59. 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 !
- 60. 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)
- 61. Being stern never helps! Toys fascinate kids Avoid using words like it doesn’t hurt Reschedule appointment if the child is hungry or sleepy .
- 62. 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
- 63. Infant , child Stroke patient Malingerers Mentally challenged
- 64. Determination of the refractive error by asking and relying on the subject When objective findings are determined- retinoscopy/AR/power of glasses/keratometry No data-takes visual acuity in assessment
- 65. Determine the sphere Determine the cylinder- power and axis Binocular balancing
- 66. IDENTIFY THE BEST VISION SPHERE MAXIMUM PLUS OR MINIMUM MINUS TOLERATED DUOCHROME TEST ESTIMATE CORRECTION BASED ON ACUITY DIVIDE BY 18 FOR SPHERE (VALID FOR MANIFEST HYPEROPIA ONLY ) DIVIDE BY 9 FOR CYLINDER Determine visual acuity Snellen ETDRS
- 67. 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 Cylinder error has a better acuity because there is a circle of least diffusion
- 68. 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
- 69. 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.
- 70. • Red background clearer and darker Myope • Green background clearer and darker hyperope
- 72. 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.
- 73. 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
- 74. Ametropia should be corrected to 6/12 before going ahead with the test The test may over minus in elderly patients
- 76. 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
- 78. Establish if the eye has astigmatism Refine the cylindrical power Refine the axis Calculate the near add
- 79. Determine the power of the cross cylinder to be used with the BCVA Flip the JCC and see if any position is better than other – to assess presence of astigmatism Then determine the axis and the power of the cylinder.
- 80. Occlude one eye Rotate the cylinder about the presumed axis ;flip Ask for any change If yes,then move the axis of lens closer to JCC axis by 10 degree steps Line up the power markings of the JCC with the axis of the lens If no change perceived with either plus or minus lenses,then initial power is correct Add the corresponding correction if needed Maintain the spherical equivalent
- 81. Clock dial charts • 30 degree steps like an analog clock;lesser accuracy. Radial line charts • Can be spaced at 10/15/30 degrees
- 83. Test monocularly .Fog the eye to make it compound myopic astigmatic.Patient tells the clearest line on the dial;Multiply by 30 = this is the cylinder axis . Cylinder power is increased until all lines are equally clear . Correct till the highest positive or the weakest negative lens gives the best vision
- 84. Astigmatic fan Needs inactive accomodation Useful in corneal opacity
- 85. 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
- 86. 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
- 87. Do not over correct for near !
- 88. Dynamic retinoscopy Refining of previous add Cross cylinder for near Amplitude of accomodation Expected age value
- 89. 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.
- 90. 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
- 92. Age 10 20 35 45 50 55 60 65 70 Dond ers 14 10 5.5 3.5 2.5 1.75 1 0.5 0.25 Hofst etter 15.5 12.5 8 5 3.5 2 0.5 0.5 0
- 93. To balance the accomodation between the two eyes Assess the best corrected acuity uniocularly
- 95. Rule out Phorias Tropias Convergence insufficiency Fusional reserves
- 96. Infrared source Fixation target Badal optometer ( position of the lens is linearly propotional to the refractive error with a constant magnification )
- 97. COLLIMATION OF IR RAYS BEAM SPLITTER REMOVES REFLECTED LIGHT FROM CORNEA LATERAL MOVEMENT OF THE SYSTEM TO FIND OPTIMAL FOCUS OF SLIT ON RETINA
- 98. Measures at least three meridians of the eye Uses sine squared function to measure the refractive power Power = sphere + ( cylinder sine 2@ )
- 99. 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
- 100. 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
- 102. 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