FREE Optics and Refraction Questions and Answers Flashcards
6 cards from real Board Certified Ophthalmologist practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 FREE Optics and Refraction Questions and Answers flashcards as text
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?
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.
Which type of astigmatism is present when one focal line falls in front of the retina and the other falls behind it?
Answer: Mixed astigmatism
Mixed astigmatism occurs when the two principal meridians focus on opposite sides of the retina.
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?
Answer: 41.1 degrees
The critical angle is calculated as sin^-1(1/1.52) = 41.1 degrees.
A prism with an apical angle of 10 degrees and refractive index of 1.5 produces what amount of deviation?
Answer: 5 prism diopters
Using the thin prism approximation, deviation = (n-1) x apical angle = (1.5-1) x 10 = 5 prism diopters.
In retinoscopy, a with-the-rule movement is observed in the horizontal meridian. What type of lens should be added to neutralize this meridian?
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.
What is the approximate accommodative demand for a 2.50 D myope who removes their spectacles to read at 40 cm?
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.