NBEO Optics & Lens Design

Question 1

What is the diopter?

Accepted Answer

The unit of measurement for the refractive power of a lens, equal to the reciprocal of the focal length in meters

Answer

A diopter (D) measures lens power. A +1.00D lens has a focal length of 1 meter. Higher diopter values indicate stronger lenses. Minus lenses diverge light (myopia correction); plus lenses converge light (hyperopia correction).

Question 2

What is astigmatism?

Accepted Answer

A refractive error caused by an irregularly curved cornea or lens that creates two focal points, causing blurred or distorted vision at all distances

Answer

In astigmatism, the cornea or lens has different curvatures in different meridians (like a football vs. a basketball), creating two focal lines instead of one focal point, corrected with cylindrical lenses.

Question 3

What is presbyopia?

Accepted Answer

The age-related loss of accommodation (near focusing ability) due to hardening of the crystalline lens, typically becoming noticeable after age 40

Answer

Presbyopia occurs as the crystalline lens gradually loses elasticity with age, reducing its ability to change shape for near focus. Corrected with reading glasses, bifocals, progressives, or multifocal contact lenses.

Question 4

What is a progressive addition lens (PAL)?

Accepted Answer

A multifocal lens with a gradual power change from distance at the top to near at the bottom, without visible dividing lines

Answer

PALs (no-line bifocals) provide seamless vision at all distances through a corridor of increasing plus power from the distance zone through intermediate to the near zone, with peripheral distortion areas.

Question 5

What is the difference between CR-39 and polycarbonate lens materials?

Accepted Answer

CR-39 has better optical clarity; polycarbonate is lighter, thinner, and significantly more impact-resistant

Answer

CR-39 plastic offers excellent optical quality and scratch resistance. Polycarbonate is 10x more impact-resistant, lighter, and thinner, making it mandatory for children's glasses, safety eyewear, and sports eyewear.

NBEO - National Board of Examiners in Optometry Practice Test

NBEO - National Board of Examiners in Optometry Practice Test

NBEO Optics & Lens Design