Board Certified Ophthalmologist FREE Optics and Refraction Questions and Answers 2 — Questions and Answers
Question 1: A patient with a cycloplegic refraction of +5.00 D requires a spectacle lens at a vertex distance of 12 mm. What is the effective power at the corneal plane?
- +5.31 D (Correct answer)
- +4.72 D
- +5.00 D
- +4.50 D
Correct answer: +5.31 D
Using the effectivity formula, the effective power at a shorter vertex distance increases for plus lenses: +5.00 / (1 - 0.012 x 5.00) = +5.31 D.
Question 2: Which type of astigmatism is present when one focal line falls in front of the retina and the other falls behind it?
- Mixed astigmatism (Correct answer)
- Simple myopic astigmatism
- Compound hyperopic astigmatism
- Simple hyperopic astigmatism
Correct answer: Mixed astigmatism
Mixed astigmatism occurs when the two principal meridians focus on opposite sides of the retina.
Question 3: What is the critical angle for total internal reflection at a crown glass-air interface if the refractive index of crown glass is 1.52?
- 41.1 degrees (Correct answer)
- 48.8 degrees
- 33.3 degrees
- 55.6 degrees
Correct answer: 41.1 degrees
The critical angle is calculated as sin^-1(1/1.52) = 41.1 degrees.
Question 4: A prism with an apical angle of 10 degrees and refractive index of 1.5 produces what amount of deviation?
- 5 prism diopters (Correct answer)
- 10 prism diopters
- 15 prism diopters
- 7.5 prism diopters
Correct answer: 5 prism diopters
Using the thin prism approximation, deviation = (n-1) x apical angle = (1.5-1) x 10 = 5 prism diopters.
Question 5: In retinoscopy, a with-the-rule movement is observed in the horizontal meridian. What type of lens should be added to neutralize this meridian?
- Plus cylinder at 180 degrees (Correct answer)
- Minus cylinder at 180 degrees
- Plus cylinder at 90 degrees
- Plus sphere only
Correct answer: Plus cylinder at 180 degrees
With movement in the horizontal meridian indicates relative hyperopia in that meridian, corrected by adding plus power at 180 degrees.
Question 6: What is the approximate accommodative demand for a 2.50 D myope who removes their spectacles to read at 40 cm?
- 0 D (Correct answer)
- 2.50 D
- 1.50 D
- 4.00 D
Correct answer: 0 D
A -2.50 D myope has a far point at 40 cm, so reading at 40 cm without glasses requires essentially no accommodation.
Board Certified Ophthalmologist FREE Optics and Refraction Questions and Answers 2
A patient with a cycloplegic refraction of +5.00 D requires a spectacle lens at a vertex distance of 12 mm.
What is the effective power at the corneal plane?