CPOA Ophthalmic Optics 5 — Questions and Answers
Question 1: What is the purpose of a trifocal lens segment compared to a bifocal?
- It provides correction for distance only
- It adds an intermediate zone between the distance and near zones (Correct answer)
- It corrects only astigmatism
- It eliminates the need for a reading segment
Correct answer: It adds an intermediate zone between the distance and near zones
A trifocal lens has three zones: distance, intermediate, and near, providing clear vision at all three working distances for presbyopic patients.
Question 2: Which neutralization technique uses a lens clock (Geneva lens measure) to determine the approximate prescription of an unknown lens?
- Keratometry
- Retinoscopy
- Lensometry with neutralization (Correct answer)
- Sagittal depth measurement
Correct answer: Lensometry with neutralization
A lens clock measures the curve on each surface of the lens, and combined with the lens index, the prescription can be approximated through surface power neutralization.
Question 3: A patient's prescription is -3.00 -1.50 x 180. If this is transposed to plus cylinder form, the result is:
- -4.50 +1.50 x 090 (Correct answer)
- -1.50 -1.50 x 090
- -4.50 +1.50 x 180
- -3.00 +1.50 x 090
Correct answer: -4.50 +1.50 x 090
To transpose: algebraically add sphere and cylinder (-3.00 + (-1.50) = -4.50), change cylinder sign (+1.50), and rotate axis 90° (180° + 90° = 90°).
Question 4: What is the purpose of UV-blocking treatment or material in ophthalmic lenses?
- To prevent lens scratching
- To protect the eye from ultraviolet radiation that can cause cataracts and macular damage (Correct answer)
- To enhance contrast sensitivity
- To reduce chromatic aberration
Correct answer: To protect the eye from ultraviolet radiation that can cause cataracts and macular damage
UV-blocking lenses absorb ultraviolet radiation (UVA and UVB) to help protect ocular tissues from cumulative UV damage linked to cataracts and macular degeneration.
Question 5: In ophthalmic optics, what does the term 'meniscus lens' describe?
- A lens with one flat and one curved surface
- A lens with both surfaces curved in the same direction (concave-convex) (Correct answer)
- A lens with equal power on both surfaces
- A bifocal lens with a curved segment
Correct answer: A lens with both surfaces curved in the same direction (concave-convex)
A meniscus lens has one convex and one concave surface curving in the same direction, which is the standard form used in modern ophthalmic lens design to reduce aberrations.
Question 6: What does the term 'slab-off' refer to in ophthalmic lens fabrication?
- Grinding the flat top edge of a bifocal segment
- Removing base-up prism from one lens to correct vertical imbalance in anisometropia (Correct answer)
- Polishing the lens periphery to reduce edge thickness
- Adding a UV protective layer to the lens surface
Correct answer: Removing base-up prism from one lens to correct vertical imbalance in anisometropia
Slab-off is a process that removes base-up prism from one lens (usually the more minus lens) to compensate for vertical prismatic imbalance caused by anisometropia when the patient looks down to read.
Question 7: What is the difference between specular and diffuse reflection in the context of ophthalmic optics?
- Specular reflection occurs only in glass lenses; diffuse in plastic
- Specular reflection is mirror-like from smooth surfaces; diffuse reflection scatters light from rough surfaces (Correct answer)
- Specular reflection increases with AR coating; diffuse decreases
- Specular refers to UV reflection; diffuse refers to visible light
Correct answer: Specular reflection is mirror-like from smooth surfaces; diffuse reflection scatters light from rough surfaces
Specular reflection follows the law of reflection from smooth surfaces (like polished lenses), while diffuse reflection scatters light in many directions from irregular or rough surfaces.
CPOA Ophthalmic Optics 5
What is the purpose of a trifocal lens segment compared to a bifocal?