Biometry and A-Scans Flashcards
7 cards from real COT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Biometry and A-Scans flashcards as text
Which of the following BEST describes the Haigis formula's approach to IOL calculation?
Answer: Uses three constants (a0, a1, a2) and measures ACD
The Haigis formula uses three lens constants and incorporates measured ACD to predict effective lens position.
On a properly aligned A-scan, the retinal spike should be:
Answer: Sharp and perpendicular (90°) with high amplitude
A perpendicular, high-amplitude retinal spike indicates the probe is aligned along the visual axis and measurement is accurate.
What is the typical axial length of an emmetropic adult eye?
Answer: 23.0–24.0 mm
The average emmetropic adult eye has an axial length of approximately 23.0–24.0 mm.
Which instrument combines keratometry, corneal topography, and optical biometry in one device?
Answer: Lenstar LS 900
The Lenstar LS 900 uses optical low coherence reflectometry (OLCR) to measure biometry and keratometry simultaneously.
In a patient with a dense posterior subcapsular cataract, the BEST biometry method is:
Answer: Immersion A-scan
Immersion A-scan is preferred when optical biometry cannot penetrate a dense cataract, as it avoids corneal compression.
The keratometry value (K) used in IOL formulas represents the:
Answer: Average corneal curvature in diopters
K values reflect the curvature of the anterior corneal surface, expressed in diopters, and are essential for IOL power calculation.
Post-LASIK eyes present a challenge for IOL calculation primarily because:
Answer: Keratometry readings underestimate the true corneal power
Standard keratometry overestimates corneal power after LASIK due to index of refraction assumptions, leading to hyperopic surprise.