Corrective Lenses Flashcards

When neutralizing a lens with a lensometer, a practitioner observes two sets of lines that are sharp but do not overlap at the same power. This indicates:

Answer: A cylindrical or sphero-cylindrical lens

When two meridians require different power settings to focus separately, the lens contains cylinder (astigmatic correction).

Photochromic lenses darken in response to:

Answer: Ultraviolet (UV) radiation

Photochromic lenses contain molecules that undergo structural changes when exposed to UV radiation, causing the lenses to darken.

What is the standard interpupillary distance (PD) measurement used when dispensing single-vision distance lenses?

Answer: Distance PD measured while patient fixates on a distant target

Distance PD is measured while the patient fixates at a distant target (6 meters or optical infinity) to align optical centers with the visual axes.

A spectacle lens prescription is written as: +1.00 +2.00 x 090. What is the total power in the 090 meridian?

Answer: +1.00 D

The cylinder axis indicates the meridian where cylinder power is zero; at 090°, only sphere power (+1.00 D) acts.

Which frame material is known for its lightweight properties, hypoallergenic nature, and use in rimless and semi-rimless mountings?

Answer: Titanium

Titanium is extremely lightweight, corrosion-resistant, and hypoallergenic, making it ideal for rimless and semi-rimless frame styles.

Prentice's Rule states that the prismatic effect of a decentered lens equals:

Answer: Power (D) × decentration (cm)

Prentice's Rule: Prism (Δ) = Power (D) × decentration (cm); decentration must be in centimeters.

A patient with a high plus prescription (+10.00 D) would likely experience which optical side effect from their thick spectacle lenses?

Answer: Magnification of objects

Plus (convex) lenses magnify images, so high plus spectacle lenses cause noticeable magnification of the wearer's visual field.