types and the mode of refraction

1. S. Arya das
Student at bhartimaiya college of opto

2. SHADOW PLAY - RETINOSCOPY

3. Myopia
Hyperopia
Astigmatism

4. 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

5. 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

6. Illumination Stage Reflex Stage
Projection Stage

7. Illumination

8. • Rays are from S1
• Image is at far point of subject
• Shadow at pupil of subject
• Projected to the examiner

9. Normal Eye
+1.50
66 cm

10. Hyperopia (Small Eyes)
+58 D

11. Myopia (Large Eyes)
+62 D

12. StreakStreak
RetinoscopyRetinoscopy

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
 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

16. 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

17. 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

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. Net - 6.00 DS
- 4.00 DS
90° Axis
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
- 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

22. RefinementRefinement
ofof
RefractionRefraction

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.  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

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

29. Duchrome
 Chromatic aberration

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.
• Increasing the converging power so that
“STRONGEST + LENSES “ are given.
P O
N F
T E
A K

32.  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 O
N F
T E
A K

33. Astigmatic dial technique

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

35. Giving Glasses

36. Giving Glasses
Hyperopia
Age
Fogging
Refinement methods
1) Less than 3 years = Full retinoscopic correction
Eg; +4.00 DS = Give + 4.00 DS
2) 3 to 8 years
Presence 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 +

37. 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
Hyperopia
Correction
with Age

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
: 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

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.

42. Bifocals

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
Bifocal to progressive
Adjust sphere first
E.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

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 
(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

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