In the trial frame scale, what does a white 5 mm reading indicate?

In the trial frame scale, what does a white 5 mm reading indicate?

• A. Closer to the cornea
• B. Farther from the cornea
• C. No significance
• D. Pupil size

Answer: (A)

The white numbers on the trial frame scale indicate the back vertex distance—the gap between the cornea and the back surface of the lens. A reading of 5 mm means the lens is very close to the eye, only five millimeters away from the cornea. This closeness matters because moving the lens closer to or farther from the eye changes the effective power the eye experiences, especially for higher prescriptions. So this reading shows the lens is nearer to the cornea, rather than farther away or having no significance, and not related to pupil size. Larger numbers would indicate a greater distance from the cornea.

The white numbers on the trial frame scale indicate the back vertex distance—the gap between the cornea and the back surface of the lens. A reading of 5 mm means the lens is very close to the eye, only five millimeters away from the cornea. This closeness matters because moving the lens closer to or farther from the eye changes the effective power the eye experiences, especially for higher prescriptions. So this reading shows the lens is nearer to the cornea, rather than farther away or having no significance, and not related to pupil size. Larger numbers would indicate a greater distance from the cornea.