NOCE Ophthalmic Optics and Formulas 3

Question 1

Transpose +2.00 −1.50 × 090 into plus cylinder form. What is the result?

Accepted Answer

+0.50 +1.50 × 180

Answer

New sphere = +2.00 + (−1.50) = +0.50; new cylinder = +1.50; new axis = 090 + 90 = 180.

Question 2

A +10.00 D lens is moved 10 mm farther from the eye. What is the approximate effective power at the eye?

Accepted Answer

+11.11 D

Answer

F_eff = F / (1 − d×F) = 10 / (1 − 0.010 × 10) = 10 / 0.90 ≈ +11.11 D.

Question 3

Using the simplified sag formula s ≈ y²/(2r), what is the sag when y = 30 mm and r = 200 mm?

Accepted Answer

2.25 mm

Answer

s = (30²) / (2 × 200) = 900 / 400 = 2.25 mm.

Question 4

What is the correct minus cylinder transposition of −3.00 +2.00 × 045?

Accepted Answer

−1.00 −2.00 × 135

Answer

New sphere = −3.00 + 2.00 = −1.00; new cylinder = −2.00; new axis = 045 + 90 = 135.

Question 5

What is the spherical equivalent of −2.00 −1.50 × 180?

Accepted Answer

−2.75 D

Answer

SE = sphere + (cylinder / 2) = −2.00 + (−1.50 / 2) = −2.00 − 0.75 = −2.75 D.

NOCE - National Opticianry Competency Examination Practice Test