NBEO Optics & Lens Design — Questions and Answers
Question 1: What is the diopter?
- The unit of measurement for the refractive power of a lens, equal to the reciprocal of the focal length in meters (Correct answer)
- A type of eye disease
- An instrument for measuring pupil size
- A unit of visual acuity
Correct answer: The unit of measurement for the refractive power of a lens, equal to the reciprocal of the focal length in meters
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?
- A refractive error caused by an irregularly curved cornea or lens that creates two focal points, causing blurred or distorted vision at all distances (Correct answer)
- Only a problem for near vision
- An age-related condition
- A disease of the retina
Correct 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
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?
- The age-related loss of accommodation (near focusing ability) due to hardening of the crystalline lens, typically becoming noticeable after age 40 (Correct answer)
- A childhood vision problem
- An infection of the eye
- A type of color blindness
Correct answer: The age-related loss of accommodation (near focusing ability) due to hardening of the crystalline lens, typically becoming noticeable after age 40
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)?
- A multifocal lens with a gradual power change from distance at the top to near at the bottom, without visible dividing lines (Correct answer)
- A lens that changes color in sunlight
- A single-vision lens with progressive tint
- A disposable contact lens
Correct answer: A multifocal lens with a gradual power change from distance at the top to near at the bottom, without visible dividing lines
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?
- CR-39 has better optical clarity; polycarbonate is lighter, thinner, and significantly more impact-resistant (Correct answer)
- They are identical materials
- CR-39 is always preferred
- Polycarbonate has better optics
Correct answer: CR-39 has better optical clarity; polycarbonate is lighter, thinner, and significantly more impact-resistant
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.
Question 6: What is prism in ophthalmic lenses?
- An optical element that shifts the apparent position of images to correct binocular vision problems like strabismus and convergence issues (Correct answer)
- A decorative lens coating
- A type of lens tint
- A measurement of lens thickness
Correct answer: An optical element that shifts the apparent position of images to correct binocular vision problems like strabismus and convergence issues
Prism lenses bend light to shift the image position, helping align images for both eyes in patients with strabismus, convergence insufficiency, or diplopia, measured in prism diopters with a specified base direction.
NBEO Optics & Lens Design
What is the diopter?