CPOA Spectacle Dispensing 4 — Questions and Answers
Question 1: Prentice's Rule states that prismatic effect (prism diopters) equals:
- Lens power divided by decentration in mm
- Lens power multiplied by decentration in cm (Correct answer)
- Decentration in mm divided by lens power
- Lens power plus decentration in mm
Correct answer: Lens power multiplied by decentration in cm
Prentice's Rule: Δ = F × c, where F is lens power in diopters and c is decentration in centimeters.
Question 2: A patient picking up new glasses complains the left lens looks darker than the right. Which is the most likely explanation for plastic frames?
- One lens has AR coating and the other does not
- The tinting process was uneven or the lenses were different materials (Correct answer)
- One lens has a higher index of refraction
- The pantoscopic tilt differs between the two sides
Correct answer: The tinting process was uneven or the lenses were different materials
Uneven tint absorption typically results from inconsistent immersion time, temperature, or different lens materials that take dye differently.
Question 3: Which temple style wraps completely around the ear and is commonly used in children's or safety frames?
- Library (skull) temple
- Riding bow (cable) temple (Correct answer)
- Hockey-end temple
- Spring hinge temple
Correct answer: Riding bow (cable) temple
Riding bow (cable) temples curl completely around the ear, providing extra retention used in active-wear, safety, and pediatric frames.
Question 4: The minimum recommended lens size for a given prescription is determined primarily by:
- The patient's pupillary distance and frame PD (Correct answer)
- The temple length
- The bridge size
- The patient's vertex distance
Correct answer: The patient's pupillary distance and frame PD
The minimum blank size must accommodate the optical center placement relative to the patient's PD and the frame's geometric center PD.
Question 5: Which coating is applied to a lens to reduce the build-up of static charge and repel dust particles?
- Hydrophobic coating
- Anti-static coating (Correct answer)
- Anti-reflective coating
- Scratch-resistant coating
Correct answer: Anti-static coating
Anti-static coatings neutralize electrostatic charges on the lens surface, helping prevent dust and lint attraction.
Question 6: When verifying a finished lens with a lensometer, the target (mires) should be focused at what position for reading the sphere power?
- The outermost ring target
- The single dot or cross target at center (Correct answer)
- The cylinder lines target only
- The prism reference point
Correct answer: The single dot or cross target at center
The sphere power is read when the central dot or cross of the lensometer target is in sharp focus, before rotating the cylinder axis.
Question 7: A frame is described as having 'spring hinges.' What is the primary benefit of this feature?
- The frame can be adjusted for pantoscopic tilt
- The temples flex outward and spring back, improving retention and durability (Correct answer)
- The bridge is flexible for wide noses
- The lens can be removed without tools
Correct answer: The temples flex outward and spring back, improving retention and durability
Spring hinges contain a tensioned mechanism that allows temples to flex beyond 90° and return to position, reducing frame stress and improving fit.
CPOA Spectacle Dispensing 4
Prentice's Rule states that prismatic effect (prism diopters) equals: