CPOA Spectacle Dispensing 3 — Questions and Answers
Question 1: What does the term 'optical center' of a lens refer to?
- The geometric center of the lens blank
- The point where light passes through without prismatic deviation (Correct answer)
- The thickest point of the lens
- The center of the frame's eye wire
Correct answer: The point where light passes through without prismatic deviation
The optical center is the point on a lens through which light travels in a straight line without being bent by prism effect.
Question 2: Pantoscopic tilt refers to:
- The inward angle of the temples
- The downward tilt of the lens bottom relative to the top (Correct answer)
- The wrap angle of the frame front
- The vertical alignment of the bridge
Correct answer: The downward tilt of the lens bottom relative to the top
Pantoscopic tilt is the angle at which the bottom of the frame tilts toward the face, typically 8–12 degrees for optimum optics.
Question 3: Which of the following best describes 'induced prism' in spectacle lenses?
- Prism intentionally prescribed to treat diplopia
- Prismatic effect caused when the eye views through a point other than the optical center (Correct answer)
- The Fresnel prism applied to lens surface
- Base-down prism in reading glasses
Correct answer: Prismatic effect caused when the eye views through a point other than the optical center
Induced (unwanted) prism occurs when the pupil is decentered from the lens optical center, creating a prismatic shift per Prentice's Rule.
Question 4: A lens with a base curve of 6.00 D and a front surface power of +6.00 D has a back surface power of -2.00 D. What is the approximate total lens power?
- +8.00 D
- +4.00 D (Correct answer)
- -4.00 D
- +6.00 D
Correct answer: +4.00 D
Approximate total power equals front surface plus back surface: +6.00 + (-2.00) = +4.00 D.
Question 5: Which adjustment corrects a frame that sits too low on the patient's face?
- Widen the nose pads
- Close (narrow) the nose pads (Correct answer)
- Increase pantoscopic tilt
- Bend temples downward
Correct answer: Close (narrow) the nose pads
Narrowing (closing) the nose pads raises the frame higher on the nose, lifting it to a better position.
Question 6: Which type of lens tint absorbs more light in the blue end of the spectrum and is often marketed to improve contrast for outdoor activities?
- Gray tint
- Green tint
- Yellow/amber tint (Correct answer)
- Rose tint
Correct answer: Yellow/amber tint
Yellow and amber tints absorb short-wavelength blue light, which can enhance contrast in hazy or low-light outdoor conditions.
Question 7: The term 'monocular PD' refers to:
- The total distance between both pupils
- The distance from each pupil to the center of the nose bridge individually (Correct answer)
- The PD measured for one eye only in monocular patients
- The near PD minus 3 mm
Correct answer: The distance from each pupil to the center of the nose bridge individually
Monocular PD measures the distance from each pupil to the midpoint of the nose separately, allowing for asymmetrical placement of optical centers.
CPOA Spectacle Dispensing 3
What does the term 'optical center' of a lens refer to?