Refraction and Retinoscopy
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Transcript of Refraction and Retinoscopy
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Dr. Dimple PrakashHead Post Graduate Training Programme
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SHADOW PLAY - RETINOSCOPY
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MyopiaHyperopia
Astigmatism
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in case of Welsch Allen retinoscope when the lens is pushed down the
mirror acts like a plane mirror and the rays are divergent.
Plane Mirror Retinoscopy
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When the lens is pushed up the mirror acts like a concave mirror so the rays are
convergent.Practical importance : in plane mirror
retinoscopy a with movement will need + lenses but in concave mirror retinoscopy
a with movement will need – lenses.
Concave Mirror Retinoscopy
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Illumination Stage Reflex Stage
Projection Stage
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Illumination
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• Rays are from S1
• Image is at far point of subject
• Shadow at pupil of subject
• Projected to the examiner
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Normal Eye
+1.50
66 cm
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Hyperopia (Small Eyes)
+58 D
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Myopia (Large Eyes)
+62 D
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StreakStreakRetinoscopyRetinoscopy
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Break :
Width : Narrowest when allingned with true axis
Intensity : Brightest when along with true axis
Skew : When axis is not assigned reflex breaking into two
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Low Errors High Errors
Speed High Low
Brilliance Bright Dull
Width Wide Narrow
Neutralization point : complete illumination of entire pupillary area.
Swirl
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Checking axis : Swirl 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.
WAKE UP
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GROSS NET
Power of lens that is held in front of the examined eye at which neutralization occurs
Following subtraction of distance and cycloplegic drops
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Distance Subtraction Cycloplegic
1 mt = 1 D
2/3 mt = 1.50 D
Atropine = -1.00 D
Homatropine = -0.50 D
Cyclopentolate = -0.75 D
Example Distance (lm) Atropine+6.00 DS +5.00 DS +4.00 DS
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Few Algebraic rules for signs of Cylinders
- - = + - 6.00 - 4.00 = - 2.00
- + = + - 6.00 + 4.00 = - 10.00
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Practice Situations
Net + 6.00
+ 4.00
Lower Value = Sphere = +4.00
Difference = Cylinder = +2.00
+ 4.00 - +6.00 = - Sign of cylinder
Axis at lower value = 180°
+ 4.00 DS / -2.00 DC @ 180° Axis
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Net - 6.00 DS
- 4.00 DS
90° Axis
180° Axis
* Lower value here is – 6.00 DSThe rest is the same
- - = +- 6.00 DS / +2.00 DC x 90° Axis
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- 8.00 DS
- 10.00 DS
- 10.00 / +2.00 DC x 180° Axis
Sample Transpositions- 2.00 DS / -4.00 DC x 180° Axis
1. Allegebric sum of the sphere and cylinder- 6.00 DS
2. Change the sign of the cylinder- 6.00 DS / +4.00 DC
3. Change the axis if above 90° = minus 90 if below 90° = add 90
- 6.00 DS / +4.00 DC @ 90 ° Axis
WAKE UP
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RefinementRefinementofof
RefractionRefraction
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Methods Easiest : fogging. Over refraction,
over retinoscopy
Duchrome testing
Jackson cross cylinder
Astigmatic dial
Astigmatic fan and block
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Jackson Cross Cylinder Components: sphere
Cylinder
Power: ½ that of cylinder
Axis of Cylinder : 2 are perpendicular to each other
Handle: 45 degrees always.
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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 +.
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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.
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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.
How it works?WAKE UP
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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 visions : Why?
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Duchrome
Chromatic aberration
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Duchrome Normal : both equal Start with Red slightly better Focus on the letters
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Hyperope of +5.00 sees green better, increase to +5.25 D so sees red better.
• Increasing the converging power so that “STRONGEST + LENSES “ are given. (asthenopia)
P ON F
T EA K
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Myope: - 5.00D sees red better leave him alone
-5.00 D sees green then – 4.75 D get the rays in front.
• “WEAKEST (– )LENSES”
P ON F
T EA K
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Astigmatic dial technique
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Fogging
Indications : Young: Recurrent Asthenopia: H/O Squeezing / frowning: Difficulty in near work
(E.g.) Needle work, Microscope
Reference 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 etc
Upto (+6.00 DS. From then upto +4.00 DS : +0.50 DS decrease+5.50, +5.00, +4.50 etc
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Giving Glasses
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Giving Glasses
Hyperopia
Age
Fogging
Refinement methods
1) Less than 3 years = Full retinoscopic correctionEg; +4.00 DS = Give + 4.00 DS
2) 3 to 8 yearsPresence of tropia
Presence of phoria
Esotropia = Full gross value subjective to AC/A ratio
Phoria = Full net optimal, under correction
Eg. Net Value
+4.00 D in phoria = +3.50 / +3.75 which is accepted
3) Adults follow : rule of strongest +
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0 1 2 3 4 5 6 7 8 9 10 11 12 YRS
HM 6.50
6.00
5.50
5.00
4.50
4.00
3.50
3.00
2.50
2.00
1.50
1.00
HyperopiaCorrection
with Age
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Giving Glasses : MYOPIA
Thumb rules Normal patients
1) From -1.00 to -6.00 DS : Full correction
2) Above -6.00 DS : Under correct to meet subjectiveness
Esotropia
High presence of -6.00 DS and above are under correctedmeet acceptance followed by optimal to full correction
ExotropiaOver correct in intermittent EXOTROPIAS
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Giving Glasses : Astigmatism
Normal patients
: 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)
WAKE UP
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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
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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.
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Bifocals
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Bifocals Working distance
0.2 m wide or smallest test type
Blurred/ not readable = near point
No doubling
Keep 1/3rd reserve
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Tips on bifocals
Keep 1/3rd reserve
Undercorrect
Full correction 23 mm of near point max (3.5D)
Prisms for convergence thereafter
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Practical Tips
Do Don't
Read Previous prescription
Bifocal to progressive
Adjust sphere firstE.g.) +1.25 DS / -0.75 DC
Change to +1.75 to +1.50
Don’t make drastic glass changes from past “Suspicion”
progressive to Bifocals
Do not try to change to higher astigmatism+1.25 DS / -1.25 DC
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Practical Tips
Do Don't
4. Try to correct the axis rather than the number
Eg) -0.75 DC @ 90° Axchange to -0.75 DC @ 100° Ax rather than -1.00 DC @ 90° Ax
Final Example-1.25 DS / -0.75 @ 80° Ax
(a) -1.50 DS / -1.75 DS with -0.75 DC @ 80° Ax
(b) -1.25 DS / -0.75 DC @ 90° Ax (c) -1.25 DS / -1.00 DC @ 80° Ax
-1.50 DS / -1.50 DC @ 80° Ax
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Make the right choice
Low powers : smile and bye bye
High plus: think!Chromatic aberrationsprismatic aberrations
High index lenses: 1.6 and 1.74
Thinner, flatter, lighter +4.00 D = high index
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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
-7.00 D above : 1.7 high index.
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Power refraction you are now armed
Retinoscopy
Interpretation of numbers
Giving glasses
Refinement of numbers
What not to do
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Dr. DIMPLE PRAKASHSenior Consultant
Pediatric and SquintHead Post Graduate Training Programme