COT - Certified Ophthalmic Technician Biometry and A-Scans Questions and Answers

Question 1

A technician performs applanation A-scan biometry and obtains an axial length of 22.50 mm.
The same eye is then measured using immersion A-scan, yielding a measurement of 22.85 mm.
What is the most likely reason for this discrepancy?

Accepted Answer

Corneal compression from the applanation probe.

Answer

Misalignment of the probe off the visual axis during applanation.

Answer

Incorrect sound velocity setting for the crystalline lens.

Answer

Patient blinking excessively during the immersion scan.

Question 2

When evaluating an A-scan waveform for accuracy, which of the following represents the ideal characteristics for the retinal spike?

Accepted Answer

A tall, steeply rising spike that is perpendicular to the baseline.

Answer

A short, broad spike followed immediately by a series of smaller spikes.

Answer

A spike that is less than 50% of the height of the anterior lens spike.

Answer

A notched or double-peaked spike just before the orbital fat signals.

Question 3

An ophthalmologist is selecting an IOL formula for a patient with a very short axial length of 21.2 mm. Which of the following formulas has traditionally been preferred for this type of eye?

Accepted Answer

Hoffer Q

Answer

SRK/T

Answer

Binkhorst

Answer

SRK II

Question 4

During an A-scan measurement, the technician fails to identify a distinct posterior lens capsule spike, and the lens thickness value appears abnormally large. This is most characteristic of:

Accepted Answer

A dense posterior subcapsular cataract.

Answer

A patient who is aphakic.

Answer

Misalignment onto the optic nerve head.

Answer

Excessive gain setting on the machine.

Question 5

A technician is preparing to perform an A-scan on a patient whose vitreous cavity is filled with silicone oil. Which of the following is the most critical machine setting to adjust for an accurate axial length measurement?

Accepted Answer

The sound velocity setting.

Answer

The signal gain amplification.

Answer

The patient's keratometry values.

Answer

The measurement mode (manual vs. automatic).

Question 6

Which of the following is a primary advantage of optical biometry (e.g., IOLMaster, Lenstar) over ultrasound A-scan biometry?

Accepted Answer

It is a non-contact procedure that avoids corneal compression.

Answer

It is significantly less expensive to acquire and maintain.

Answer

It can successfully measure axial length through a mature, opaque cataract.

Answer

It measures the eye's anatomic axis for better surgical planning.

A technician performs applanation A-scan biometry and obtains an axial length of 22.50 mm.The same eye is then measured using immersion A-scan, yielding a measurement of 22.85 mm.What is the most likely reason for this discrepancy?

A technician performs applanation A-scan biometry and obtains an axial length of 22.50 mm.
The same eye is then measured using immersion A-scan, yielding a measurement of 22.85 mm.
What is the most likely reason for this discrepancy?