Cataract and Lens Flashcards
7 cards from real ABO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Cataract and Lens flashcards as text
In an average-length eye, an axial length measurement error of 1 mm results in approximately what postoperative refractive error?
Answer: 2.5-3.0 D
A 1 mm axial length error produces roughly 2.5-3.0 D of refractive error, making axial length the most critical biometric variable.
A patient with prior myopic LASIK undergoes cataract surgery using standard keratometry and a standard third-generation formula. What refractive surprise is most likely?
Answer: Hyperopic surprise
After myopic ablation, standard keratometry overestimates corneal power and the formula's ELP prediction is off, leading to an underpowered IOL and hyperopic surprise.
When performing contact A-scan biometry on an eye filled with silicone oil, what error occurs if the default vitreous sound velocity is not corrected?
Answer: Axial length is falsely long
Sound travels slower through silicone oil (~980 m/s) than vitreous, so an uncorrected A-scan reports a falsely long axial length.
After posterior capsule rupture, a 3-piece IOL is placed in the ciliary sulcus instead of the capsular bag. How should the IOL power typically be adjusted for a mid-range power lens?
Answer: Decrease by approximately 0.5-1.0 D
Sulcus placement moves the optic anteriorly, increasing effective power, so the IOL power is reduced by about 0.5-1.0 D.
Which IOL formula has traditionally been favored for short eyes (axial length less than 22 mm)?
Answer: Hoffer Q
Hoffer Q has historically performed best in short eyes, while SRK/T is favored for long eyes.
A toric IOL rotates 10 degrees off its intended axis after surgery. Approximately what percentage of its cylindrical correction is lost?
Answer: About 33%
Each degree of toric IOL misalignment reduces cylinder correction by roughly 3.3%, so 10 degrees loses about one-third.
If posterior corneal astigmatism is ignored when planning a toric IOL based only on anterior keratometry, what is the typical result?
Answer: Overcorrection of with-the-rule astigmatism
The posterior cornea usually contributes against-the-rule astigmatism, so ignoring it leads to overcorrecting with-the-rule and undercorrecting against-the-rule astigmatism.