JCAHPO Corrective Lenses 2 — Questions and Answers
Question 1: A patient has a spectacle prescription of -3.00 -1.50 x 090. What is the power in the 180-degree meridian?
- -3.00 D
- -4.50 D (Correct answer)
- -1.50 D
- +1.50 D
Correct answer: -4.50 D
The power at 180° equals the sphere plus the cylinder: -3.00 + (-1.50) = -4.50 D.
Question 2: Which type of bifocal segment provides the widest reading area at the bottom of the lens?
- Executive (Franklin) bifocal (Correct answer)
- Round segment bifocal
- Flat-top (D-seg) bifocal
- Blended bifocal
Correct answer: Executive (Franklin) bifocal
The Executive or Franklin bifocal has a full-width segment line across the entire lens, providing the widest reading area.
Question 3: A prism of 2Δ base-in is prescribed for the right eye. In which direction will the image appear to shift for the patient?
- Nasally (toward the nose)
- Temporally (away from the nose) (Correct answer)
- Superiorly
- Inferiorly
Correct answer: Temporally (away from the nose)
Prism displaces images toward the apex; base-in means the apex is out (temporal), so the image shifts temporally.
Question 4: What is the vertex distance, and why does it matter for high-power prescriptions?
- Distance from cornea to lens; affects effective power for powers >±4.00 D (Correct answer)
- Distance between the two lenses; affects interpupillary distance
- Thickness of the lens center; affects weight
- Distance from lens to the retina; affects magnification only
Correct answer: Distance from cornea to lens; affects effective power for powers >±4.00 D
Vertex distance is the distance from the back surface of the spectacle lens to the cornea, and it significantly affects effective power for prescriptions above ±4.00 D.
Question 5: Polycarbonate lenses are most often recommended for which patient population?
- Patients with presbyopia needing bifocals
- Children and patients requiring impact-resistant lenses (Correct answer)
- Patients with high myopia needing thin lenses
- Patients with UV sensitivity
Correct answer: Children and patients requiring impact-resistant lenses
Polycarbonate is highly impact-resistant and is the material of choice for children and monocular patients requiring eye protection.
Question 6: Which lens design is characterized by a gradual change in power from distance to near with no visible segment line?
- Flat-top bifocal
- Trifocal
- Progressive addition lens (PAL) (Correct answer)
- Occupational bifocal
Correct answer: Progressive addition lens (PAL)
Progressive addition lenses (PALs) provide a smooth corridor of increasing power from the distance zone to the near zone without a visible dividing line.
Question 7: A contact lens prescription reads +2.50 D. When converted to a spectacle prescription for a vertex distance of 12 mm, the spectacle power should be approximately:
- +2.43 D (Correct answer)
- +2.57 D
- +2.50 D (no change)
- +2.75 D
Correct answer: +2.43 D
Moving a plus lens away from the eye reduces effective power; the spectacle equivalent is slightly less than the contact lens power.
JCAHPO Corrective Lenses 2
A patient has a spectacle prescription of -3.00 -1.50 x 090.
What is the power in the 180-degree meridian?