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Optics and Refraction Principles Flashcards

7 cards from real ABO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Optics and Refraction Principles flashcards as text

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

    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.

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

    Answer: +0.50 D

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

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

    Answer: -1.00 +2.00 x 090

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

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

    Answer: Add minus sphere

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

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

    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.

  6. On a fogged astigmatic dial, the patient sees the 6-12 o'clock line darkest. Where is the minus cylinder axis placed?

    Answer: 180 degrees

    Multiply the lower clock number by 30 (6 x 30 = 180) to get the minus cylinder axis.

  7. With a 67 cm working distance, retinoscopy reflex is neutralized with a +3.00 D lens. What is the refractive error?

    Answer: +1.50 D

    Subtract the working distance lens (1/0.67 m = 1.50 D) from the gross retinoscopy value.