Optics and Refraction Flashcards
7 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 7 Optics and Refraction flashcards as text
Which higher-order aberration is most typical of keratoconus?
Answer: Vertical coma
An inferiorly displaced cone produces a vertically asymmetric cornea, so vertical coma is the dominant higher-order aberration.
Why do aspheric IOLs often have negative spherical aberration?
Answer: To offset the cornea's positive spherical aberration
The average cornea has positive spherical aberration, and an IOL with negative spherical aberration reduces the eye's total and improves contrast sensitivity.
Why do polarized sunglasses reduce glare from water and roads?
Answer: Light reflected off horizontal surfaces is mostly horizontally polarized, and the lenses block it
Glare reflected from horizontal surfaces is mainly horizontally polarized, and polarized lenses with a vertical transmission axis block it.
What wavelength does the Nd:YAG laser used for posterior capsulotomy emit?
Answer: 1064 nm
The Nd:YAG laser emits infrared light at 1064 nm and works by photodisruption. 532 nm is its frequency-doubled output.
A presbyope has 2.00 D of accommodation and wants to read at 40 cm, keeping half the accommodation in reserve. What add is needed?
Answer: +1.50 D
Reading at 40 cm takes 2.50 D. Using 1.00 D (half the amplitude) leaves +1.50 D to come from the add.
Which bifocal segment design minimizes image jump?
Answer: Flat-top segment
Image jump depends on the distance from the top of the segment to its optical center. A flat-top's optical center sits near the top, which minimizes the jump.
A spherical rigid gas-permeable contact lens mainly neutralizes which type of astigmatism?
Answer: Anterior corneal astigmatism
The tear lens under a rigid lens fills in the toric front surface of the cornea, which neutralizes anterior corneal astigmatism. Lenticular astigmatism remains as residual astigmatism.