4. Plane Mirror Retinoscopy
in case of Welsch Allen retinoscope
when the lens is pushed down the
mirror acts like a plane mirror and the
rays are divergent.
5. Concave 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.
13. 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
14. Low Errors High Errors
Speed High Low
Brilliance Bright Dull
Width Wide Narrow
Neutralization point : complete illumination of entire
pupillary area.
Swirl
15. 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.
16. GROSS NET
Power of lens Following
that is held in subtraction of
front of the distance and
examined eye cycloplegic
at which drops
neutralization
occurs
17. Distance Subtraction Cycloplegic
1 mt = 1 D Atropine = -1.00 D
2/3 mt = 1.50 D Homatropine = -0.50 D
Cyclopentolate = -0.75 D
Example Distance (lm) Atropine
+6.00 DS +5.00 DS +4.00 DS
18. Few Algebraic rules for signs of Cylinders
- - = + - 6.00 - 4.00 = - 2.00
- + = + - 6.00 + 4.00 = - 10.00
19. 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
20. 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
21. - 8.00 DS
WAKE UP
- 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
23. Methods
Easiest : fogging. Over refraction,
over retinoscopy
Duchrome testing
Jackson cross cylinder
Astigmatic dial
Astigmatic fan and block
24. Jackson Cross Cylinder
Components: sphere
Cylinder
Power: ½ that of cylinder
Axis of Cylinder : 2 are
perpendicular to each other
Handle: 45 degrees always.
25. 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 +.
26. 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.
27. 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.
28. 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
30. Duchrome
Normal : both equal
Start with Red slightly better
Focus on the letters
31. Hyperope of +5.00 sees green
better, increase to +5.25 D so sees
red better.
TE
A K
• Increasing the converging power so that
“STRONGEST + LENSES “ are given.
(asthenopia)
32. Myope: - 5.00D sees red better leave
him alone
-5.00 D sees green then – 4.75 D get
the rays in front.
PO
N F
• “WEAKEST (– )LENSES”
34. 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
36. 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 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 +
38. 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 corrected
meet acceptance followed by optimal to full correction
Exotropia
Over correct in intermittent EXOTROPIAS
39. 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)
40. 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
41. 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.
43. Bifocals
Working distance
0.2 m wide or smallest test
type
Blurred/ not readable = near
point
No doubling
Keep 1/3rd reserve
44. Tips on bifocals
Keep 1/3rd reserve
Undercorrect
Full correction 23 mm of near
point max (3.5D)
Prisms for convergence thereafter
45. Practical Tips
Do Don't
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
46. Practical Tips
Do Don't
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 Ax
Final 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 J
L -1.50 DS / -1.50 DC @ 80 Ax
47. 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
48. 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
49. Power refraction you are now armed
Retinoscopy
Interpretation of numbers
Giving glasses
Refinement of numbers
What not to do
50. Dr. DIMPLE PRAKASH
Senior Consultant
Pediatric and Squint
Head Post Graduate Training Programme