American Board of Opticianry (ABO) Practice Test 2026 - Free ABO Practice Questions and Study Guide

Question: 1 / 400

In optical dispensing, what is the term for the distance from the back surface of the lens to the front surface of the cornea?

Focal length

Vertex distance

The term for the distance from the back surface of the lens to the front surface of the cornea is known as vertex distance. This measurement is crucial in optical dispensing because it affects the effective power of the lens as perceived by the patient. Changes in vertex distance can alter the way light is focused on the retina, which can impact the overall visual acuity for the wearer.

In practice, understanding vertex distance is important for ensuring that prescription lenses are fitted in a way that optimizes visual performance. If the lenses are positioned too far away or too close to the eye, the wearer might experience distorted vision or discomfort.

Thus, properly measuring and considering vertex distance during the fitting process helps in achieving the best possible visual correction for the patient.

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Optical center distance

Lenticular distance

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