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Clinical Refraction Clinical Refraction D avi d M eyer OD FAAO Object i ves Revi ew concept s r el at ed t o cl i ni cal r ef r act i on Lear n pr act i cal appr oaches t o dai l y pat i ent car e Ret inoscopy Very important for: • Obj ect i ve r ef r act i on det er mi nat i on • D et ect i ng opt i cal aber r at i ons ( ker at oconus) • Opaci t i es ( PSC) U sef ul for: • Infants • Wiggly children • Adults and children unabl e t o cooper at e/poor at subj ect i ve r ef r act i on Ret inoscopy U se pl ano mi r r or set t i ng • Sl eeve al l t he way down H ave pt f i xat e on l ar ge di st ance obj ect • Rel axed accommodat i on • 20/400 letter • M ay need t o cycl opl ege ki ds Ret inoscopy Thr ee basi c t ypes of r ef l exes: • “With” motion • “Against” motion • “Neutral” or no motion I nvol ves t he “ f ar poi nt ” • The f ar t hest away t he eye can see cl ear l y wi t h accommodat i on ent i r el y at rest is the FAR POINT (more on this later) Ret inoscopy and t he Far Point I f t he f ar poi nt i s BETW EEN t he exami ner and t he pat i ent , t hen di ver gence of t he light rays occur • “Against” motion I f t he f ar poi nt i s i s BEH I N D t he exami ner , t he l i ght moves i n t he same di r ect i on of t he sweep • “With” motion If the light fills the pupil and does not move, then NEUTRALITY is found • M ovi ng back woul d cause t he f ar poi nt t o be bet ween you and t he pat i ent , so AGAI N ST motion would be seen. Opposite if moving forward. http://www.cyber-sight.org/bins/news_page.asp?cid=1-9436-9441-9482 Ret inoscopy Quiz You are using a retinoscope on Cloyd, your -2.00 D myopic patient I f you wer e si t t i ng 100cm away, what mot i on woul d you see? Cloyd’s far point: 1/D = 1/2 = 0.50m (or 50cm) At 50cm, so the far point is between you and him: “Against” motion At 50cm, you would see “neutral” At any distance closer than 50cm, you would see “with” Ret inoscopy Char act er i st i cs of t he r ef l ex: • Speed . The closer you are, the faster the reflex speed • Brilliance . Brighter reflex as neutrality is approached . “With” reflexes are usually brighter than “against” • Width . The reflex broadens as you approach neutrality Ret inoscopy “With” motion - add plus “Against” motion - add minus Ret inoscopy Working Distance: • Based on how f ar away you ar e f r om t he pat i ent . Inverse relationship • Subtracted from the power of the correcting lens If you are sitting___away Then subtract: 50cm 2.00D 67cm 1.50D 100cm 1.00D Ret inoscopy Finding the axis • The eye i s made up of t wo pr i nci pal mer i di ans • N eut r al i ze t he l ess pl us axi s f i r st • Then, r ot at e t he st r eak 90 degr ees. You shoul d see “ wi t h” mot i on • Align the axis of the phoropter with your streak and add plus cyl until “neutral” is found You are doing retinoscopy on an aphakic child with Down Syndrome. With the streak oriented horizontally you get a neutral reflex with a +22 D lens. With the streak oriented vertically you get a neutral reflex with a +27 D lens. Assume a working distance of 50 cm. What is the distance Rx of the child? +22 -2 +20 +27 -2 +25 Answer: +20.00 +5.00 x 090 +20.00 +5.00 x 90 Subject i ve Refract i on Astigmatic Dial Technique • Rar el y used • St eps: . Fog the patient by adding more (+) sphere . Identify the blackest and sharpest lines . Add plus cylinder with the axis parallel to the blackest and sharpest line until all lines appear equal (plus cyl) . Reduce (+) sphere to un-fog the patient Subject i ve Refract i on -Cr os s -Cylinder Technique By far the most common method +0.25 • Jack son cr oss cyl i nder . -0.25 +0.50 x 180 -0.25 • Refine axis before refining power . Position the JCC’s principal meridians 45 degrees away from the correcting cyl . “Straddle the line” . “Chase the white” (plus cyl) • Refine the power . Align the JCC with the principal meridians of the correcting lens Axis refinement Power refinement Subject i ve Refract i on -Cr os s -Cylinder Technique D on’t f or get about spher i cal equi val ent ! For ever y 0.50 change i n cyl , make a 0.25 change i n t he spher e Cylinder Spherical Equivalent = Sphere + 2 Example: Natalie’s Rx: +2.00 +3.00 x 180 What is the spherical equivalent? 2 + 3/2 = +3.50 Subject i ve Refract i on -Refining the Sphere Goal : The st r ongest ( +) spher e ( or weakest ( -) spher e) t hat yi el ds t he best VA Reduce ( +) spher e unt i l opt i mal VA i s r eached • Watch out for “darker and smaller” = likely over-mi nused D uochr ome Test • RAM -GAP (red add minus, green add plus) • Gr een has shor t er wavel engt hs, r ed has l onger . Green wavelengths focus anterior to red Red is darker and blacker. By adding minus... ...then green becomes darker and blacker Subject i ve Refract i on -Binocular Balance Fogging • Rar el y used • U ses a +2.00 D spher e over each eye and compar e Prism Dissociation • Much more common • Add ver t i cal pr i sm t o one or bot h eyes t o cr eat e t wo i mages • Add pl us t o t he cl ear est i mage Prism Dissociation OD has BD prism in front of it and sees this “The top line is more sharp and clear” F Z B D E OS has BU prism in front of it and sees this F Z B D E If Base DOWN prism was in front of the right eye, then add +0.25 in OD until both lines appear equal in clarity. A Final Word on Subjective Refraction... Ever y 0.25 change i s APPROXI M ATELY equal t o one i mpr oved l i ne i n VA Exampl e: • H edwi g’s habi t ual Rx and VA i n OD : -1.50 DS 20/30 • Adding -0.25 should get him to about 20/25 • Adding another -0.25 should get him to about 20/20 • Expect ed r ef r act i on: -2.00 DS Spect acle Correct i on of Amet ropi as Far Poi nt • The f ar t hest away t he eye can see cl ear l y wi t h accommodat i on ent i r el y at rest is the FAR POINT . For myopia: far point is between infinity and the patient . For hyperopia: far point is behind the retina • To correct the ametropic eye the correcting lens must place its image (Secondary focal point – f2) at t he eye’s f ar poi nt . • The i mage of t he f ar poi nt pl ane becomes t he obj ect t hat i s f ocused on t he r et i na Vert ex Dist ance Changi ng t he posi t i on of t he cor r ect i ng l ens changes t he r el at i onshi p bet ween F2 and t he eye’s f ar poi nt • Very important for prescriptions greater than +5.00/-5.00 . Standard glasses vertex is 12mm • Critical for contact lens prescribing Following Example: • Lonzo wears +10.00 glasses that sit 10mm in front of his eyes. If he prefers to wear those lenses at 5mm in front of his eyes, what power should you prescribe? A +10.00 lens is moved from 10mm to 5mm away from the cornea What power lens has a focal length of 95mm (9.5 cm)? 1 1 D = = = +10.5 D f .095 m 10 mm +10 5 mm +10.5 Far Point - 90mm behind the cornea 95 mm 100 mm Prescribing for Children Myopia • Ret i noscopy and cycl opl egi a ar e cr i t i cal • Chi l dr en t ol er at e cyl i nder wel l • Consi der cont act l enses f or hi gh mi nus or ani somet r opi c eyes Prescribing for Children Hyperopia • M or e compl ex t han myopi a - pat i ent somet i mes can’t see di st ance or near • Of t en accompany st r abi smus and accommodat i on i ssues • Ret i noscopy and cycl opl egi a ar e very critical • Except i n cases of esot r opi a, “ cut t he pl us” .
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