What is the maximum vertex distance shown on the trial frame scale?

What is the maximum vertex distance shown on the trial frame scale?

• A. 0 to 15 mm
• B. 0 to 25 mm
• C. 0 to 5 mm
• D. 0 to 50 mm

Answer: (A)

Vertex distance is the space between the back surface of the lens and the eye, and in a trial frame you adjust this distance using a built-in scale. In most clinical trial frames, the scale runs from 0 up to a maximum that corresponds to typical eyewear fittings. The common maximum shown on the scale is 15 mm, which aligns with the average range of vertex distances encountered when refraction and lens power are adjusted to resemble real-world wear. Distances like 25 or 50 mm would place the lens far too close or far from the eye for ordinary frames, and a range only up to 5 mm would not cover the practical needs for vertex adjustments. Therefore, 0 to 15 mm is the standard maximum vertex distance represented on the trial frame scale.

Vertex distance is the space between the back surface of the lens and the eye, and in a trial frame you adjust this distance using a built-in scale. In most clinical trial frames, the scale runs from 0 up to a maximum that corresponds to typical eyewear fittings. The common maximum shown on the scale is 15 mm, which aligns with the average range of vertex distances encountered when refraction and lens power are adjusted to resemble real-world wear. Distances like 25 or 50 mm would place the lens far too close or far from the eye for ordinary frames, and a range only up to 5 mm would not cover the practical needs for vertex adjustments. Therefore, 0 to 15 mm is the standard maximum vertex distance represented on the trial frame scale.