JCAHPO Corrective Lenses 4 โ Questions and Answers
Question 1: 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:
- A spherical lens
- A prismatic lens
- A cylindrical or sphero-cylindrical lens (Correct answer)
- A bifocal lens
Correct answer: A cylindrical or sphero-cylindrical lens
When two meridians require different power settings to focus separately, the lens contains cylinder (astigmatic correction).
Question 2: Photochromic lenses darken in response to:
- Heat from sunlight
- Ultraviolet (UV) radiation (Correct answer)
- Blue light from digital screens
- Infrared radiation
Correct answer: Ultraviolet (UV) radiation
Photochromic lenses contain molecules that undergo structural changes when exposed to UV radiation, causing the lenses to darken.
Question 3: What is the standard interpupillary distance (PD) measurement used when dispensing single-vision distance lenses?
- Near PD measured at 40 cm
- Distance PD measured while patient fixates on a distant target (Correct answer)
- The average of near and far PD
- Monocular PD measured from the nose only
Correct 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.
Question 4: A spectacle lens prescription is written as: +1.00 +2.00 x 090. What is the total power in the 090 meridian?
- +1.00 D (Correct answer)
- +3.00 D
- +2.00 D
- +1.00 D + prismatic effect
Correct answer: +1.00 D
The cylinder axis indicates the meridian where cylinder power is zero; at 090ยฐ, only sphere power (+1.00 D) acts.
Question 5: Which frame material is known for its lightweight properties, hypoallergenic nature, and use in rimless and semi-rimless mountings?
- Zyl (cellulose acetate)
- Titanium (Correct answer)
- Monel (nickel alloy)
- Nylon
Correct answer: Titanium
Titanium is extremely lightweight, corrosion-resistant, and hypoallergenic, making it ideal for rimless and semi-rimless frame styles.
Question 6: Prentice's Rule states that the prismatic effect of a decentered lens equals:
- Power (D) ร decentration (cm) (Correct answer)
- Power (D) รท decentration (mm)
- Decentration (mm) รท power (D)
- Power (D) ร decentration (mm)
Correct answer: Power (D) ร decentration (cm)
Prentice's Rule: Prism (ฮ) = Power (D) ร decentration (cm); decentration must be in centimeters.
Question 7: A patient with a high plus prescription (+10.00 D) would likely experience which optical side effect from their thick spectacle lenses?
- Minification of objects
- Magnification of objects (Correct answer)
- No change in perceived image size
- Pin-cushion distortion only
Correct answer: Magnification of objects
Plus (convex) lenses magnify images, so high plus spectacle lenses cause noticeable magnification of the wearer's visual field.
JCAHPO Corrective Lenses 4
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: