Refraction and Retinoscopy
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Transcript of Refraction and Retinoscopy
Dr. Dimple PrakashHead Post Graduate Training Programme
SHADOW PLAY - RETINOSCOPY
MyopiaHyperopia
Astigmatism
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
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
Illumination Stage Reflex Stage
Projection Stage
Illumination
• Rays are from S1
• Image is at far point of subject
• Shadow at pupil of subject
• Projected to the examiner
Normal Eye
+1.50
66 cm
Hyperopia (Small Eyes)
+58 D
Myopia (Large Eyes)
+62 D
StreakStreakRetinoscopyRetinoscopy
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
Low Errors High Errors
Speed High Low
Brilliance Bright Dull
Width Wide Narrow
Neutralization point : complete illumination of entire pupillary area.
Swirl
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
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
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
Few Algebraic rules for signs of Cylinders
- - = + - 6.00 - 4.00 = - 2.00
- + = + - 6.00 + 4.00 = - 10.00
Practice Situations
Net + 6.00
+ 4.00
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
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
- 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
RefinementRefinementofof
RefractionRefraction
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.
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
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?
Duchrome
Chromatic aberration
Duchrome Normal : both equal Start with Red slightly better Focus on the letters
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
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
Astigmatic dial technique
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
Giving Glasses
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 +
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
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
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
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
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 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
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
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
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.
Power refraction you are now armed
Retinoscopy
Interpretation of numbers
Giving glasses
Refinement of numbers
What not to do
Dr. DIMPLE PRAKASHSenior Consultant
Pediatric and SquintHead Post Graduate Training Programme