Learn Connect Succeed JCAHPO Regional Meetings 2017
Refractometry JCAHPO Continuing Education Program Phoenix and Scottsdale, AZ Craig Simms BSc, COMT, CDOS, ROUB Director of Education, IJCAHPO Program Director, KOTC Financial Interest I have no financial interest in any products or equipment I may show, mention, or talk about they are simply the machines and products that we use in our clinic. Objectives Optics review Plus cylinder retinoscopy Minus cylinder retinoscopy Manifest refraction State of Light Divergence Convergence Parallel Divergence Rays that spread apart from an object Minus power Natural state of light Convergence Rays that come toward one another Plus power Not a natural state and must have been changed by passing through an optical system 1
Zero Vergence Rays that are parallel No power Not a natural state and must have been changed by passing through an optical system Spherical Convex Lenses One or both surfaces are curved outward Consider 2 prisms stacked base to base Focal point is determined by the curvature of both surfaces Plus lenses Converge light to a focus behind the lens Spherical Convex Lenses Spherical Concave Lenses One or both surfaces are curved inward Consider 2 prisms stacked apex to apex Focal point is determined by the curvature of both surfaces Emergent rays are divergent Cannot be focussed behind the lens Imaginary focus in front of lens Minus lenses Spherical Concave Lenses Cylindrical Lens A flat surface and a curved surface Rays striking the curved surface are refracted Rays striking the flat surface are not refracted Refracting power in one direction Zero power 90 degrees away (axis) Refracts light to a focal line...not a focal point Focal line is parallel to the cylinder axis and perpendicular to its power 2
Cylindrical Lens Cylindrical lens Designated by axis not by the power meridian Can be plus or minus Conoid of Sturm Spherocylindrical lens is essentially 2 cylinders Produces 2 focal lines 90 degrees apart Distance of each is determined by the power of its individual component Conoid of Sturm or Sturm s interval is the space between the 2 focal lines Review of plus and minus lenses Review of plus and minus lenses Review of plus and minus lenses Review of plus and minus lenses Using the cornea as a reference Plus lenses move the focal point towards the cornea Minus lenses move the focal point away from the cornea 3
Refractive Errors Astigmatism Myopia : near-sighted Hyperopia : far-sighted Astigmatism : different focal lengths in the principle meridians Definitions Refraction Determination of an eye s refractive error and the best corrective lenses to be prescribed Refractometry Objective testing to determine the combination of spheres and cylinders that will optically correct an eye without determining what prescription a patient will accept 3 The clinical procedure for determining a patient s refractive error 4 Reference 3 Reference 3 Retinoscopy Retinoscopy Measuring an eye s refractive error by using a retinoscope You can t learn retinoscopy by reading a book 1 Jack Copeland Reference 3 4
Retinoscopy Objective measure of the optical power of the eye Illuminate the inside of the eye Observe the light that is reflected from the retina Light is altered by the different components of the eye Cornea Lens Vitreous Length of the eye By analyzing how the emerging light changes we can determine the refractive power of the eye Reference 1 Retinoscopy Objective test Evaluate the eye as an optical system No feedback from the patient Does not depend on the patient s vision or judgement Will work on schematic eyes Can be performed on: Children / infants Unresponsive patients Patients with language barriers Reference 1 The Retinoscope Light source Bulb with a linear filament which projects a line or streak Rotate the direction of the streak by turning the sleeve Condensing lens Focuses rays of light from the bulb onto the mirror The Retinoscope Focusing sleeve Varies the distance between the bulb and the lens to allow the retinoscope to project light that is either diverging or converging Controls the vergence of the light and the meridian of the streak Mirror Bends the light at a right angle so it projects from the instrument Reference 1 Reference 1 The Retinoscope Focusing sleeve Question: Sleeve up or sleeve down? Answer: Depends You want the light coming from the retinoscope to be diverging Cannot be focused on the wall Reference 1 5
Retinoscopy What do we do with the retinoscope? Look through the retinoscope Direct it into the patient s eye Move the streak perpendicular to its orientation Retinoscopy What will you see? With motion = focal point is behind the retina Retinoscopy What will you see? Against motion = focal point is in front of the retina Retinoscopy What is really happening? Emerging rays run through the eye s optics and are heading for the eye s far point If emmetropic parallel (neutral) If myopic converging (against motion) If hyperopic diverging (with motion) Reference 2 Emmetropia light emerges parallel pupil is full (neutral) Myopia far point is between the eye and your light against motion 6
Hyperopia far point is behind your light with motion Retinoscopy Our end point is neutral How do we get there? With Motion focal point is behind the retina Add plus lenses to move the focal point onto the retina With Motion focal point is behind the retina Add plus lenses to move the focal point onto the retina Against Motion focal point is in front of the retina Add minus lenses to move the focal point onto the retina Against Motion focal point is in front of the retina Add minus lenses to move the focal point onto the retina 7
The Reflex With motion Against motion What about with motion for a +1.00 versus a +12.00 or -1.00 versus -12.00? As a focal point approaches the neutral point it becomes brighter, wider, and moves faster The Reflex Analyse the reflex concentrating on the light not on the shadow for: Brightness Speed Movement Size The Reflex Well behind the retina The Reflex Behind the retina but closer Small reflex Slow movement May look dull Larger reflex Little faster movement A little brighter The Reflex Behind the retina but closer still The Reflex neutral Larger reflex Little faster movement A little brighter Pupil is filled in No movement Bright 8
Retinoscopy Procedure plus cylinder Shine the streak in the eye Analyse the reflex Check all meridians Spin the reflex 360 degrees Find the 2 principal axes Will almost always be 90 degrees apart Retinoscopy Procedure plus cylinder With the 2 principal meridians you may have: With motion in both (same) With motion in both (different) Against motion in both (same) Against motion in both (different) With motion in one and against motion in the other With motion in one and neutral in the other Against motion in one and neutral in the other With motion in both (same) With motion in both (same) Both focal points are the same distance behind the retina = no astigmatism Add plus sphere lenses until neutral Add plus sphere lenses until neutral With motion in both (different) With motion in both (different) Both focal points are behind the retina but at different distances = astigmatism Pick the reflex that is closest to neutral Brightest Fastest Add plus sphere lenses until neutral Switch to the other meridian and neutralize with plus cylinder lenses Add plus sphere lenses until neutral Switch to the other meridian and neutralize with plus cylinder lenses 9
With motion in both (different) All other possibilities Add minus until both focal points are behind the retina (with motion) Pick the reflex that is closest to neutral Brightest Fastest Add plus sphere lenses until neutral Switch to the other meridian and neutralize with plus cylinder lenses Add plus sphere lenses until neutral Switch to the other meridian and neutralize with plus cylinder lenses Retinoscopy Procedure minus cylinder Just as corned beef goes with cabbage, plus cylinders complement retinoscopy. John M. Corboy, M.D. But there is a way to perform retinoscopy in minus cylinder Retinoscopy Procedure minus cylinder Shine the streak in the eye Analyse the reflex Check all meridians Spin the reflex 360 degrees Find the 2 principal axes Will almost always be 90 degrees apart Retinoscopy Procedure minus cylinder Evaluate all meridians Convert all meridians to AGAINST motion using spheres Reduce the sphere, comparing all meridians, until one meridian is neutral Apply minus cylinder to neutralize the opposite meridian BUT, you have to work in against motion! Retinoscopy Procedure minus cylinder Double-click method (with motion) Evaluate all meridians Convert all meridians to WITH motion using spheres Reduce the sphere, comparing all meridians, until one meridian is neutral Set the minus cylinder 90 degrees from the cylinder meridian Neutralize the WITH reflex by using the cylinder and sphere lenses: for each -0.25 or click of cylinder click in +0.25 sphere 10
Retinoscopy Procedure minus cylinder Double-click method (with motion) For every -0.25 cylinder added 90 degrees from the cylinder axis add +0.25 sphere This transposes the minus cylinder into a plus cylinder in the correct meridian Eg: cylinder axis is at 180 degree and showing WITH -0.25 pl +0.25 +0.25 pl +0.25 Fixation during retinoscopy Eyes must be still and accommodation relaxed Patient can fixate on a distant, non-accommodative target Light at the end of the room look out the door look at the end of the room 6/120 letter on the acuity chart Target should lack fine details Fine details can stimulate accommodation These make the patient view the target at optical infinity Arriving wave front is plano Patient is not adding any plus to the system Working Distance Some textbook suggest putting in a working lens of +1.00 to +1.75 depending on how far you are from the patient Others prefer to perform retinoscopy then subtract the +1.00 to +1.75 after retinoscopy is done Average arm s length is roughly 66 cm or 26 inches which corresponds to a +1.50 Working Distance A patient s glasses are best when corrected for infinity When we perform retinoscopy we are neutralizing the eye to the plane of the retinoscope not infinity It is rather inconvenient to perform retinoscopy from infinity We perform retinoscopy at a working distance then account for it as if we are refracting from infinity Subjective Refraction Goal is to find the lens combination that gives the best acuity under conditions approximating daily seeing manifest refraction cyclo refraction if performed while dilated Performed after retinoscopy and after working distance accounted for Requires patient input Subjective Refraction Procedure Test the patient s acuity Should be able to obtain 6/12 (20/40) to 6/15 (20/50) with retinoscopy Perform manifest on each eye separately to complete the refraction But first 11
Phoropter Instrument used for refractometry Contains large number of combinations of lenses Spheres Cylinders Jackson cross cylinder Prisms Contains ancillary testing items Maddox rods PD adjustment Phoropter Jackson cross cylinder Sphere Cylinder axis Cylinder power Level PD adjustment Vertex distance Jackson Cross Cylinder Compound lens having a net minus power in one meridian and an equal net plus power in the other Eg -1.00 + 2.00 =1.00 dioptre cross cylinder Jackson Cross Cylinder Labelled by their axis Red dot = minus cylinder White dot = plus cylinder -0.50 + 1.00 = 0.50 dioptre cross cylinder Used to refine the cylinder axis and cylinder power -0.25 + 0.50 = 0.25 dioptre cross cylinder Jackson Cross Cylinder Idea is to present the patient with 2 different choices Refine the cylinder axis first Position the cross cylinder to straddle the cylinder axis Technique used to refine the cylinder axis and cylinder power I am going to show you 2 different lenses. Both may look blurry. Please tell me which you like better. 12
Refine the cylinder axis first Flip the cross cylinder and determine which is clearer to the patient Refine the cylinder axis first Flip the cross cylinder and determine which is clearer to the patient Better 1? or better 2? Refine the cylinder axis first Rotate the cylinder axis towards the white dot for plus cylinder and towards the red dot for minus cylinder Refine the cylinder axis first Rotate the cylinder axis towards the white dot for plus cylinder Rotate 15 o until the patient chooses the other direction 90 75 50 90 75 50 2 Refine the cylinder axis first Rotate back 10 o Always chase the white for plus cylinder and red for minus cylinder Refine the cylinder axis first Rotate back 5 o Always chase the white for plus cylinder and red for minus cylinder End point = where patient reports no difference 90 75 50 90 75 50 13
Refine the cylinder power next Basically collapsing the conoid of Sturm Circle of least confusion must be kept on the retina Anytime cylinder power is adjusted by 0.50 D you change the sphere power by 0.25 D in the opposite direction OR refine the sphere at the end Refine the cylinder power next Position the cross cylinder on axis Flip the cross cylinder and determine which is clearer to the patient Better 1? Refine the cylinder power next Position the cross cylinder on axis Flip the cross cylinder and determine which is clearer to the patient Refine the cylinder power next If the red dot is preferred add minus cylinder power or Take away plus or better 2? Refine the cylinder power next If the white dot is preferred add plus power Or take away minus End point = where patient reports no difference Refine the sphere power Adjust sphere to optimal position Be aware of not over minusing a myope Rule of thumb Only give more minus if it improves vision by an entire line Advanced techniques to avoid giving too much minus Refine the cylinder with the retinoscope Balancing Duochrome test 14
Refine the axis with the retinoscope During retinoscopy you can refine the axis of the cylinder by 2 methods: 1. As you are approaching the neutral position of the cylinder, move the sleeve of the retinoscope towards the diverging position Refine the axis with the retinoscope Both methods narrow the beam Watch for 3 properties Thickness phenomenon Give you a better look at the axis Once the axis is pinpointed, continue neutralizing 2. Lean forward Both methods narrow the beam Give you a better look at the axis Once the axis is pinpointed, continue neutralizing Duochrome Test Chromatic Aberration Red-Green Test Performed after refraction is completed and you have achieved the best corrected vision for each eye individually Uses longitudinal chromatic aberration to help fine tune the refractive error Chromatic Aberration Duochrome Test Red-Green Test Ask the patient this question: Which letters appear more clear, the letters on the red side or the letters on the green side? 15
Duochrome Test Duochrome Test If red add minus If green add plus Duochrome Test If the same = end point Duochrome Test What if your patient is colour deficient? No problem, it works on optics not colour perception, it will still work. Balancing Especially important if glasses are to be prescribed Performed after refinement You now have the best vision in each eye separately Balance the vision under binocular conditions Place a light fog (+0.75 D) before both eyes Ask the patient to compare the blurred letters while you alternatively cover each eye Give the better eye +0.25 D until the end point End point: equally bad Remove the fog Take out what you initially put in The patient may accept +0.25 D more in the one eye Balancing Right eye Left eye Original prescription -4.50 + 1.25 x 22-4.25 + 0.75 x 31 Apply light fog (+0.75) -3.75 + 1.25 x 22-3.50 + 0.75 x 31 Which eye is more clear? Patient: right Add +0.25 to right Which eye is more clear? Patient: right Add +0.25 to right Which eye is more clear? Patient: equally blurry End point. Remove original light fog. -3.50 + 1.25 x 22-3.50 + 0.75 x 31-3.25 + 1.25 x 22-3.50 + 0.75 x 31-4.00 + 1.25 x 22-4.25 + 0.75 x 31 16
References 1. The Retinoscopy Book, A Manual for Beginners, John M Corboy, MD, Charles B. Slack 1979 2. Basic Refraction Techniques, David D. Michaels, Raven Press, Ltd 1988 3. Dictionary of Eye Terminology, 5 th edition, Barbara Cassin, Triad Publishing Company 2006 4. Fundamentals for Ophthalmic Technical Personnel, Barbara Cassin, W.B Saunders Company 1995 Refractometry JCAHPO Continuing Education Program Phoenix and Scottsdale, AZ Craig Simms BSc, COMT, CDOS, ROUB Director of Education, IJCAHPO Program Director, KOTC 17