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Plane Mirror Retinoscopy in case of Welsch Allen retinoscope when the lens is pushed down themirror acts like a plane mirror and the rays are divergent.
Concave Mirror Retinoscopy When the lens is pushed up the mirroracts like a concave mirror so the rays are convergent. Practical importance : in plane mirrorretinoscopy a with movement will need +lenses but in concave mirror retinoscopy a with movement will need – lenses.
Break :Width : Narrowest whenallingned with true axisIntensity : Brightest whenalong with true axisSkew : When axis is notassigned reflex breakinginto two
Low Errors High ErrorsSpeed High LowBrilliance Bright DullWidth Wide NarrowNeutralization point : complete illumination of entirepupillary area.Swirl
Checking axis : Swirl WAKE UP 2.00DC @ 80 Add 45 degrees = 125 Minus 45 degrees = 35 Keep the streak at 125 and 35 Note the width : should be equal Side that is less : change axis slowly towards wider side.
GROSS NETPower of lens Followingthat is held in subtraction offront of the distance andexamined eye cycloplegicat which dropsneutralizationoccurs
Distance Subtraction Cycloplegic 1 mt = 1 D Atropine = -1.00 D 2/3 mt = 1.50 D Homatropine = -0.50 D Cyclopentolate = -0.75 DExample Distance (lm) Atropine+6.00 DS +5.00 DS +4.00 DS
Few Algebraic rules for signs of Cylinders- - = + - 6.00 - 4.00 = - 2.00- + = + - 6.00 + 4.00 = - 10.00
Practice Situations Net + 6.00 + 4.00Lower Value = Sphere = +4.00Difference = Cylinder = +2.00 + 4.00 - +6.00 = - Sign of cylinderAxis at lower value = 180 + 4.00 DS / -2.00 DC @ 180 Axis
90 Axis Net - 6.00 DS - 4.00 DS 180 Axis* Lower value here is – 6.00 DS The rest is the same - - = +- 6.00 DS / +2.00 DC x 90 Axis
- 8.00 DS WAKE UP - 10.00 DS - 10.00 / +2.00 DC x 180 AxisSample Transpositions - 2.00 DS / -4.00 DC x 180 Axis1. Allegebric sum of the sphere and cylinder - 6.00 DS2. Change the sign of the cylinder - 6.00 DS / +4.00 DC3. Change the axis if above 90 = minus 90 if below 90 = add 90 - 6.00 DS / +4.00 DC @ 90 Axis
Methods Easiest : fogging. Over refraction, over retinoscopy Duchrome testing Jackson cross cylinder Astigmatic dial Astigmatic fan and block
Jackson Cross Cylinder Components: sphere Cylinder Power: ½ that of cylinder Axis of Cylinder : 2 are perpendicular to each other Handle: 45 degrees always.
How it works? Axis first: handle in direction of the cylinder in the frame already. Eg) 2.00DC at 180 then keep handle at 180 Va chart 2 lines above least visible. eg)6/12 if BCVA is 6/6. Flip + 0.50 or – in front of patient. At best vision point, rotate the DC by 10 degrees towards the red mark in case of – and towards white mark in +.
E.g.) DC in trial frame= +2.00DC @ 180 BCVA CLEAR when +0.50 DC is in front Rotate 10 degrees towards white mark +2.00 DC@ 170.
How it works? WAKE UP Power of DC. This is easy. Keeping the correct axis. Flip the JC by + or – and then add or subtract the correct power. E.g.) DC in trial frame = +2.00,Va better at +0.50 DC then final value= +2.50 DC. If equal Va at 2 flips: correct power.
Summary Most plus or least minus sphere: BCVA Va chart 2 lines above least visible. eg)6/12 if BCVA is 6/6. No cylinder, still flip at 90,180,45,135. Axis first : Why? Lower powers 0.25 for 20/30 Va .Flip + 0.50 or 1.00 for lower
Fogging Indications : Young : Recurrent Asthenopia : H/O Squeezing / frowning : Difficulty in near work (E.g.) Needle work, MicroscopeReference Chart :If we start pt +20.00 DS upto +16 D: Decrease in lens in strengths of +2.00 DS(E.g.) +20.00 D = Next lens + 18.00 DS+16 D TO +12/10 D: Decrease in strengths of 1.00 DS (E.g.) +10.00 +9.00 DS, +8.00 etcUpto (+6.00 DS. From then upto +4.00 DS : +0.50 DS decrease+5.50, +5.00, +4.50 etc
Giving Glasses Age Hyperopia Fogging Refinement methods 1) Less than 3 years = Full retinoscopic correction Eg; +4.00 DS = Give + 4.00 DS Presence of tropia 2) 3 to 8 years Presence of phoriaEsotropia = Full gross value subjective to AC/A ratioPhoria = Full net optimal, under correctionEg. Net Value +4.00 D in phoria = +3.50 / +3.75 which is accepted 3) Adults follow : rule of strongest +
Giving Glasses : MYOPIAThumb rules Normal patients1) From -1.00 to -6.00 DS : Full correction2) Above -6.00 DS : Under correct to meet subjectiveness EsotropiaHigh presence of -6.00 DS and above are under correctedmeet acceptance followed by optimal to full correction ExotropiaOver correct in intermittent EXOTROPIAS
Giving Glasses : Astigmatism Normal patients WAKE UP: In a child less than 3 years = 1.25 DC, Regular: Older than 3 years = all astigmatism to be corrected• Child : follow-up 6 months• Adult yearly• Frequent change : over correct (0.25 D)
Giving glasses: child Ideal frame: large, sturdy, well balanced Ideal lenses: plastic, polycarbonates Ideal refraction: Less than 3 years: solely on retinoscopy All strabismus : retinoscopy Beyond 3 years: myopes do not need
Cycloplegic studies Rosenbaum and associates: atropine estimation of hyperopia 0.34 D more as compared to homatropine Hurol et al: no difference between 2 and 3 days of cycloplegia Stolovich: 8 instillations vs 4 instillations.
Bifocals Working distance 0.2 m wide or smallest test type Blurred/ not readable = near point No doubling Keep 1/3rd reserve
Tips on bifocals Keep 1/3rd reserve Undercorrect Full correction 23 mm of near point max (3.5D) Prisms for convergence thereafter
Practical Tips Do Dont Read Previous prescription Don’t make drastic glass changes from past “Suspicion” Bifocal to progressive progressive to Bifocals Adjust sphere first Do not try to change to E.g.) +1.25 DS / -0.75 DC higher astigmatism Change to +1.75 to +1.50 +1.25 DS / -1.25 DC
Practical Tips Do Dont 4. Try to correct the axis rather than the number Eg) -0.75 DC @ 90 Ax change to -0.75 DC @ 100 Ax rather than -1.00 DC @ 90 AxFinal Example-1.25 DS / -0.75 @ 80 Ax(a) -1.50 DS / -1.75 DS with -0.75 DC @ 80 Ax J(b) -1.25 DS / -0.75 DC @ 90 Ax J(c) -1.25 DS / -1.00 DC @ 80 Ax JL -1.50 DS / -1.50 DC @ 80 Ax
Make the right choice Low powers : smile and bye bye High plus: think! Chromatic aberrations prismatic aberrations High index lenses: 1.6 and 1.74 Thinner, flatter, lighter +4.00 D = high index
Gets higher : plastic lenticular lenses Aspheric lenses : curves that flatten away from the center. Prismatic effects Myopes: higher powers -4.00 above 1.6 high index
Power refraction you are now armed Retinoscopy Interpretation of numbers Giving glasses Refinement of numbers What not to do
Dr. DIMPLE PRAKASH Senior Consultant Pediatric and SquintHead Post Graduate Training Programme