Subjective Refraction- Refining Cylinder Power with Sphere Compensation

Question 1

Does the patient focus on a near or distant target

Answer 1

distant circular target.

Question 2

When working in plus cyl, what do you do first?

Answer 2

hold the plus JCC axis over the plus cyl axis in the
trial frame (position 3- this increases the cyl power).

Ask the patient to:
Look at the O. Does the O look rounder and clearer with lens 3 [position 3] or lens 4 [position 4 ~twist 180 degrees, this places the minus JCC axis over the plus cyl axis in the trial frame to decrease the cyl power] or about the same?

Question 3

What to do if position 3 is preferred?

Answer 3

add +0.50 cyl to the plus cyl and add -0.25 sphere. This sphere compensation when adjusting the cyl ensures the spherical equivalent of the lenses is maintained (spherical equivalent =sphere +cyl/2). To maintain the spherical equivalent, the sphere must be changed by half the amount of the cyl and in the opposite direction.

Question 4

What to do if position 4 is preferred?

Answer 4

reduce the plus cyl power by 0.50 cyl and add +0.25 sphere to maintain the same spherical equivalent.

Question 5

What to do if cyl power is changed and sphere compensated for?

Answer 5

recheck the axis and challenge the cyl power again. If you do not trust the cyl obtained, reduce the cyl (or remove if small} and see if the patient prefers this (ie. test for rejection of cyl), since patients are more likely to prefer under- rather than over- astigmatic correction.

Question 6

How long do you keep going for?

Answer 6

until the patient reports that position 1 is same as 2, and position 3 is the same as 4

Question 7

What to do after refining cylindrical axis and power?

Answer 7

Re-check the acuity, then proceed to the duochrome test.