COT Biometry and A-Scans 4

Question 1

Which of the following BEST describes the Haigis formula's approach to IOL calculation?

Accepted Answer

Uses three constants (a0, a1, a2) and measures ACD

Answer

The Haigis formula uses three lens constants and incorporates measured ACD to predict effective lens position.

Question 2

On a properly aligned A-scan, the retinal spike should be:

Accepted Answer

Sharp and perpendicular (90°) with high amplitude

Answer

A perpendicular, high-amplitude retinal spike indicates the probe is aligned along the visual axis and measurement is accurate.

Question 3

What is the typical axial length of an emmetropic adult eye?

Accepted Answer

23.0–24.0 mm

Answer

The average emmetropic adult eye has an axial length of approximately 23.0–24.0 mm.

Question 4

Which instrument combines keratometry, corneal topography, and optical biometry in one device?

Accepted Answer

Lenstar LS 900

Answer

The Lenstar LS 900 uses optical low coherence reflectometry (OLCR) to measure biometry and keratometry simultaneously.

Question 5

In a patient with a dense posterior subcapsular cataract, the BEST biometry method is:

Accepted Answer

Immersion A-scan

Answer

Immersion A-scan is preferred when optical biometry cannot penetrate a dense cataract, as it avoids corneal compression.

COT - Certified Ophthalmic Technician Practice Test