ABO Optics and Refraction Principles 2

Question 1

When refining cylinder axis with a Jackson cross cylinder, how is the cross cylinder positioned?

Accepted Answer

Its principal meridians straddle the cylinder axis at 45 degrees

Answer

For axis refinement the JCC axes straddle the correcting cylinder axis, with the handle aligned along it.

Question 2

What is the spherical equivalent of +2.00 -3.00 x 090?

Accepted Answer

+0.50 D

Answer

Spherical equivalent = sphere + half the cylinder = +2.00 + (-1.50) = +0.50 D.

Question 3

What is the plus-cylinder transposition of +1.00 -2.00 x 180?

Accepted Answer

-1.00 +2.00 x 090

Answer

Add the cylinder to the sphere, flip the cylinder sign, and rotate the axis 90 degrees.

Question 4

During the duochrome test, a patient reports letters on the red side are clearer. What should be done?

Accepted Answer

Add minus sphere

Answer

Red clearer means the focus is anterior to the retina (relatively myopic), so minus is added.

Question 5

What is the main purpose of fogging a patient before using an astigmatic dial?

Accepted Answer

To relax accommodation and place both focal lines in front of the retina

Answer

Fogging makes the eye artificially myopic so accommodation cannot shift the conoid of Sturm.

ABO - American Board of Ophthalmology Practice Test