Retinoscopy transposition + power cross

Question 1

What is more negative

Answer 1

The distance correction is more negative than the RET results

Question 2

When is the distance correction done

Answer 2

After finding RET result

Question 3

What is the working distance

Answer 3

2/3m OR 1.5 D

Question 4

Principles of transposition

Answer 4

• Cyl stays the same
• Working distance is +1.50
• Minus 1.50 to sphere

Question 5

Example 1

Answer 5

RET
+2.00/ - 1.00 x 90

Distance correction
0.50/ -1.00 x 90

Question 6

Example 2

Answer 6

RET
-15.25/ +2.50 x 90

Distance correction
-16.75/ +2.50 x 90

Question 7

Power cross

Answer 7

Recorded per beam while doing RET

Question 8

Power cross step 1

Answer 8

Draw a line in the direction you move the beam.
Write the power of the lens that gives you reversal on this line

Question 9

Power cross step 2

Answer 9

Rotate the beam to find the second meridian
Draw a line in this direction
Write the power of the lens that gives you reversal on this line

Question 10

Power cross step 3

Answer 10

Narrow the beam to find the orientation of one of the lines
Make sure you write the number on the correct line of your power cross

Question 11

Power cross step 4

Answer 11

Write your working distance next to the power cross

Question 12

Power cross- transposition step 1

Answer 12

Transpose to sphere/cylinder notation using the following steps:
-Write the most positive as the sphere
-The difference between the -two powers is the negative cylinder power
-The direction of the most positive power meridian is the negative cylinder axis

Example in ppt:
+1.25/-2.25 x 60
(NB. This is the retinoscopy result, NOT the distance correction.)

Question 13

Power cross- transposition step 2

Answer 13

Allow for your working distance (in dioptres) and change the sphere only.
Remember, the distance correction is always more negative than the retinoscopy result
Example in ppt:
Distance correction would be: -0.25/-2.25 x 60