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 undergoes keratometry revealing readings of 44.00 D at 90 degrees and 42.00 D at 180 degrees. What is the type and amount of corneal astigmatism?
Answer: 2.00 D with-the-rule astigmatism
The steeper meridian at 90 degrees with 2.00 D difference defines with-the-rule corneal astigmatism.
Which aberration causes a point source of light to appear as a comet-shaped blur when imaged through a spherical lens peripherally?
Answer: Coma
Coma produces an asymmetric, comet-shaped image of off-axis point sources due to varying magnification across the lens aperture.
What is the dioptric power of a thin lens with a focal length of 25 cm?
Answer: +4.00 D
Power in diopters equals the reciprocal of the focal length in meters: 1/0.25 = 4.00 D.
During Jackson cross-cylinder testing at axis 90 degrees, the patient reports the red dot (minus axis at 90) is clearer. What adjustment should be made?
Answer: Rotate the correcting cylinder axis toward 90 degrees
When the patient prefers the minus axis position, the correcting cylinder axis should be rotated toward that position.
What is the Prentice rule formula for calculating prismatic effect?
Answer: Prism (PD) = decentration (cm) x lens power (D)
The Prentice rule states that prismatic effect in prism diopters equals the decentration in centimeters multiplied by the lens power in diopters.
Which intraocular lens formula is most appropriate for eyes with axial lengths shorter than 22 mm?
Answer: Hoffer Q
The Hoffer Q formula is most accurate for short eyes with axial lengths under 22 mm due to its superior effective lens position prediction in these cases.