NOCE Ophthalmic Optics and Formulas 3 — Questions and Answers
Question 1: Transpose +2.00 −1.50 × 090 into plus cylinder form. What is the result?
- +0.50 +1.50 × 180 (Correct answer)
- +2.00 +1.50 × 180
- +0.50 +1.50 × 090
- −0.50 +1.50 × 180
Correct answer: +0.50 +1.50 × 180
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?
- +9.09 D
- +10.00 D
- +11.11 D (Correct answer)
- +12.00 D
Correct answer: +11.11 D
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?
- 1.13 mm
- 2.25 mm (Correct answer)
- 4.50 mm
- 0.56 mm
Correct answer: 2.25 mm
s = (30²) / (2 × 200) = 900 / 400 = 2.25 mm.
Question 4: What is the correct minus cylinder transposition of −3.00 +2.00 × 045?
- −1.00 −2.00 × 135 (Correct answer)
- −3.00 −2.00 × 135
- +1.00 −2.00 × 135
- −1.00 +2.00 × 135
Correct answer: −1.00 −2.00 × 135
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?
- −2.00 D
- −2.50 D
- −2.75 D (Correct answer)
- −3.50 D
Correct answer: −2.75 D
SE = sphere + (cylinder / 2) = −2.00 + (−1.50 / 2) = −2.00 − 0.75 = −2.75 D.
Question 6: For the prescription −2.00 −1.00 × 090, what is the power in the 180° meridian?
- −1.00 D
- −2.00 D
- −3.00 D (Correct answer)
- +1.00 D
Correct answer: −3.00 D
With cylinder axis at 090, maximum power acts at 180°: −2.00 + (−1.00) = −3.00 D.
Question 7: When light travels from air (n = 1.00) into glass (n = 1.50) at an oblique angle, it bends toward the normal because:
- The speed of light increases in glass
- The speed of light decreases in glass (Correct answer)
- The wavelength increases in glass
- The angle of incidence equals the angle of refraction
Correct answer: The speed of light decreases in glass
Light slows down in a denser medium, causing it to refract toward the normal per Snell's law.
NOCE Ophthalmic Optics and Formulas 3
Transpose +2.00 −1.50 × 090 into plus cylinder form.
What is the result?