Practice Quiz

Ophthalmic Technician

Category - Lensometry and Spectacle Skills

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How is vertex distance measured?
  1. From the back of the glasses to the front of the cornea
  2. From the front of the glasses to the outer margin of the orbit
  3. From the back of the glasses to the bridge of the nose
  4. From the front of the glasses to closed eyelids without corrections
Explanation
Answer: A - Vertex distance is measured from the back of the glasses to the front of the cornea.

Calculation of the vertex distance is very important for prescriptions of higher powers, especially over and above 4 diopters. The effective power of the lenses reduces when they are placed closer to the eye and vice versa.
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