CPOA Ophthalmic Optics 2 — Questions and Answers
Question 1: A patient's prescription reads +2.50 -1.25 x 090. What type of lens is indicated?
- Simple myopic lens
- Compound hyperopic astigmatic lens (Correct answer)
- Simple hyperopic lens
- Mixed astigmatic lens
Correct answer: Compound hyperopic astigmatic lens
A plus sphere combined with a minus cylinder indicates a compound hyperopic astigmatic correction.
Question 2: Which term describes the bending of light as it passes from one medium to another of different density?
- Reflection
- Diffraction
- Refraction (Correct answer)
- Absorption
Correct answer: Refraction
Refraction is the change in direction of light as it crosses the boundary between two media with different indices of refraction.
Question 3: What is the vertex distance, and why does it matter in ophthalmic prescriptions?
- The width of the lens; affects cosmetics
- The distance from the back of the lens to the cornea; affects effective power (Correct answer)
- The distance between the two lenses; affects binocularity
- The thickness of the lens center; affects weight
Correct answer: The distance from the back of the lens to the cornea; affects effective power
Vertex distance is the distance from the back surface of a lens to the corneal apex, and it affects the effective power delivered to the eye, especially in high prescriptions.
Question 4: A lens with a shorter focal length has which property?
- Lower power
- Higher power (Correct answer)
- Smaller diameter
- Greater weight
Correct answer: Higher power
Lens power in diopters equals 1 divided by the focal length in meters, so a shorter focal length means greater power.
Question 5: Which type of prism is incorporated into spectacle lenses to treat binocular vision disorders?
- Fresnel prism
- Prentice prism
- Base-in or base-out prism (Correct answer)
- Slab-off prism
Correct answer: Base-in or base-out prism
Base-in or base-out prism is prescribed to help patients with convergence or divergence problems align their eyes properly.
Question 6: What does the term 'index of refraction' measure in ophthalmic lens materials?
- The lens's resistance to scratching
- How much the material bends light relative to air (Correct answer)
- The optical clarity of the lens
- The ultraviolet absorption capacity
Correct answer: How much the material bends light relative to air
The index of refraction is the ratio of the speed of light in air to its speed in the lens material, indicating how much the material bends light.
Question 7: When a patient's optical center is decentered from their pupil center, what optical effect occurs?
- Chromatic aberration
- Spherical aberration
- Unwanted prismatic effect (Correct answer)
- Increased magnification
Correct answer: Unwanted prismatic effect
According to Prentice's rule, decentering a lens produces an unwanted prismatic effect proportional to the lens power and the amount of decentration.
CPOA Ophthalmic Optics 2
A patient's prescription reads +2.50 -1.25 x 090.
What type of lens is indicated?