Certified Ophthalmic Medical Technologist (COMT) Practice Exam

In contact A-scan biometry, what does the first or left-most spike on the screen represent?

1. The lens

2. The retina

3. A combination of the probe tip and the cornea

4. The vitreous body

The correct answer is: A combination of the probe tip and the cornea

In contact A-scan biometry, the first or left-most spike on the screen represents the combined reflection from the probe tip and the cornea. This initial spike is critical in calibrating the measurements taken because it establishes a reference point for the distance to the eye's structures. The probe tip makes contact with the eye, and the sound waves emitted reflect off the front surface of the cornea, generating this first spike. The timing of the reflections is used to calculate distances accurately throughout the eye. Understanding this fundamental representation is important for interpreting the A-scan results correctly, as it ensures that subsequent measurements, such as those from the lens, vitreous body, or retina, are accurate in relation to the cornea's position. This foundational knowledge is essential in fields such as ophthalmology, where precise measurements are critical for procedures like cataract surgery or intraocular lens calculations.