ABO Optics and Refraction Principles 2 — Questions and Answers
Question 1: When refining cylinder axis with a Jackson cross cylinder, how is the cross cylinder positioned?
- Its minus axis is aligned with the cylinder axis
- Its plus axis is aligned with the cylinder axis
- Its handle is perpendicular to the cylinder axis
- Its principal meridians straddle the cylinder axis at 45 degrees (Correct answer)
Correct answer: Its principal meridians straddle the cylinder axis at 45 degrees
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?
- -0.50 D
- +1.00 D
- +0.50 D (Correct answer)
- -1.00 D
Correct answer: +0.50 D
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?
- -1.00 +2.00 x 180
- -1.00 +2.00 x 045
- +3.00 -2.00 x 090
- -1.00 +2.00 x 090 (Correct answer)
Correct answer: -1.00 +2.00 x 090
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?
- Add plus sphere
- Increase cylinder power
- Add minus sphere (Correct answer)
- Rotate the cylinder axis
Correct answer: Add minus sphere
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?
- To enlarge the pupil
- To neutralize the spherical component completely
- To reduce chromatic aberration
- To relax accommodation and place both focal lines in front of the retina (Correct answer)
Correct answer: To relax accommodation and place both focal lines in front of the retina
Fogging makes the eye artificially myopic so accommodation cannot shift the conoid of Sturm.
Question 6: On a fogged astigmatic dial, the patient sees the 6-12 o'clock line darkest. Where is the minus cylinder axis placed?
- 90 degrees
- 135 degrees
- 45 degrees
- 180 degrees (Correct answer)
Correct answer: 180 degrees
Multiply the lower clock number by 30 (6 x 30 = 180) to get the minus cylinder axis.
Question 7: With a 67 cm working distance, retinoscopy reflex is neutralized with a +3.00 D lens. What is the refractive error?
- +4.50 D
- +3.00 D
- +1.50 D (Correct answer)
- -1.50 D
Correct answer: +1.50 D
Subtract the working distance lens (1/0.67 m = 1.50 D) from the gross retinoscopy value.
ABO Optics and Refraction Principles 2
When refining cylinder axis with a Jackson cross cylinder, how is the cross cylinder positioned?