Lens and Cataract 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 Lens and Cataract flashcards as text
For an eye with an axial length of 21.0 mm, which IOL formula has traditionally been preferred over SRK/T?
Answer: Hoffer Q
Hoffer Q (and newer formulas such as Haigis or Barrett) predicts better than SRK/T in short eyes under 22 mm.
An axial length measurement error of 1 mm produces approximately how much postoperative refractive error?
Answer: 2.5-3.0 D
In an average eye, a 1 mm error in axial length causes roughly 2.5-3.0 D of refractive error, and more in short eyes.
After prior myopic LASIK, using standard keratometry in a conventional IOL formula typically causes which refractive surprise?
Answer: Hyperopic surprise from overestimated corneal power
Standard keratometry overestimates the true power of the flattened cornea after myopic ablation, so too weak an IOL is chosen and the patient ends up hyperopic.
In an eye filled with silicone oil, an uncorrected contact A-scan ultrasound measurement will:
Answer: Overestimate the axial length
Sound travels more slowly through silicone oil (about 980 m/s) than through vitreous, so the device reads the eye as falsely long.
A 3-piece IOL calculated for in-the-bag fixation has to be placed in the ciliary sulcus. How should the power usually be adjusted?
Answer: Decrease by about 0.5-1.0 D
Sulcus fixation puts the optic further anterior, which increases its effective power, so the IOL power is lowered by about 0.5-1.0 D depending on the IOL power.
How much cylindrical correction does a toric IOL lose for each degree it is rotated off axis?
Answer: About 3.3%
Each degree of misalignment loses about 3.3% of the cylinder correction, so a 30-degree rotation removes the astigmatic benefit entirely.
Compared with contact A-scan ultrasound, optical biometry (partial coherence interferometry) usually has which limitation?
Answer: It cannot measure through dense posterior subcapsular or mature cataracts
Optical biometers need a clear enough optical path, so dense cataracts can block the measurement and ultrasound is needed instead.