COT Biometry and A-Scans 3

Question 1

In A-scan biometry, the velocity used for the vitreous cavity is approximately:

Accepted Answer

1532 m/s

Answer

The vitreous humor has a sound velocity of approximately 1532 m/s, similar to water.

Question 2

Which measurement does optical biometry (IOLMaster) rely on rather than ultrasound?

Accepted Answer

Partial coherence interferometry

Answer

Optical biometry uses partial coherence interferometry (PCI) to measure axial length with high precision.

Question 3

A-scan biometry measures axial length as the distance from the:

Accepted Answer

Corneal vertex to the fovea

Answer

Axial length is measured from the anterior corneal surface (vertex) to the fovea (macula).

Question 4

When performing A-scan on a silicone oil-filled eye, the technician must:

Accepted Answer

Use a silicone-specific velocity setting (~980 m/s)

Answer

Silicone oil has a much lower sound velocity (~980 m/s) than vitreous, requiring adjustment to avoid axial length errors.

Question 5

The A-constant in IOL power calculation is specific to:

Accepted Answer

A particular IOL model and its position in the eye

Answer

The A-constant is lens-specific and accounts for the IOL's design and expected effective lens position.

COT - Certified Ophthalmic Technician Practice Test