Ophthalmic Optics and Lenses Flashcards

A prism base direction of 'base-up' in the right eye will cause the image seen by that eye to be displaced:

Answer: Downward

Prism displaces images toward the apex, so base-up prism causes the image to appear displaced downward (toward the apex, which is down).

What is the minimum lens thickness required by ANSI Z80.1 for dress eyewear in most materials?

Answer: 1.0 mm

ANSI Z80.1 requires a minimum center thickness of 1.0 mm for most dress eyewear lens materials (except glass, which is 2.0 mm).

The distance vision zone of a progressive addition lens is located:

Answer: Above the fitting cross

In a PAL, the distance zone is positioned above the fitting cross, with the intermediate corridor below and near zone at the bottom.

Which measurement determines where to place the optical center of a single-vision lens vertically?

Answer: Monocular pupillary height

Monocular pupillary height (measured from the lowest point of the frame to the pupil center) determines vertical optical center placement for single-vision lenses.

When a minus cylinder lens is held at a distance and rotated, the scissors effect seen with a retinoscope indicates:

Answer: Oblique cylinder axis

The scissors motion (two reflexes moving in opposite directions) seen on retinoscopy indicates that cylinder is present with an oblique axis.

Polycarbonate lenses require an anti-scratch coating because:

Answer: The material is inherently soft and scratches easily

Polycarbonate is a relatively soft material compared to CR-39 or glass, making scratch-resistant coating essential for durability.

The image formed by a converging lens when the object is placed between the focal point and the lens is:

Answer: Virtual, erect, and magnified

When an object is inside the focal length of a converging lens, the image is virtual (same side as object), erect, and magnified — this is the principle of a magnifying glass.