COT Optometry 3 — Questions and Answers
Question 1: A patient wearing +2.50 D lenses moves a held object away and the image appears to move in the same direction. This is called:
- Against motion
- With motion (Correct answer)
- Scissors motion
- Neutral motion
Correct answer: With motion
Plus lenses act as converging lenses and produce 'with' apparent motion when the object is beyond the focal point.
Question 2: What does the vertex distance affect most significantly in high-powered prescriptions?
- Pupillary distance
- Effective power of the lens (Correct answer)
- Lens tint
- Frame size selection
Correct answer: Effective power of the lens
Vertex distance changes the effective power of a lens; this effect is clinically significant for prescriptions exceeding ±4.00 D.
Question 3: Which refractive surgery procedure reshapes the cornea using a microkeratome or laser to create a flap before ablation?
- PRK
- LASIK (Correct answer)
- LASEK
- RK
Correct answer: LASIK
LASIK (Laser-Assisted In Situ Keratomileusis) involves creating a corneal flap before excimer laser ablation of the stromal bed.
Question 4: A patient with 20/200 best-corrected visual acuity in the better eye meets the definition of legal blindness in the US. What is the other criterion for legal blindness?
- Visual field less than 10 degrees
- Visual field less than 20 degrees (Correct answer)
- Contrast sensitivity below 1.0 log units
- IOP greater than 21 mmHg
Correct answer: Visual field less than 20 degrees
Legal blindness is defined as best-corrected VA of 20/200 or worse, OR a visual field of 20 degrees or less in the better eye.
Question 5: Induced prism from decentered lenses can be calculated using Prentice's Rule. What is the induced prism for a -4.00 D lens decentered 5 mm?
- 0.8 prism diopters
- 2.0 prism diopters (Correct answer)
- 4.0 prism diopters
- 20 prism diopters
Correct answer: 2.0 prism diopters
Prentice's Rule: prism (Δ) = diopters × decentration (cm) = 4.00 × 0.5 = 2.0 prism diopters.
Question 6: Which lens design provides the widest clear optical zone and is preferred for high-power prescriptions to minimize aberrations?
- Flat-top bifocal
- Aspheric lens (Correct answer)
- Toric lens
- Fresnel prism lens
Correct answer: Aspheric lens
Aspheric lens designs reduce peripheral aberrations and distortion, making them particularly beneficial for high-powered prescriptions.
Question 7: When converting a minus cylinder prescription to plus cylinder form, -2.00 -1.00 x 045 becomes:
- -3.00 +1.00 x 135 (Correct answer)
- -1.00 +1.00 x 135
- -3.00 +1.00 x 045
- -1.00 -1.00 x 135
Correct answer: -3.00 +1.00 x 135
To transpose: new sphere = algebraic sum (-2.00 + -1.00 = -3.00), new cylinder = same magnitude opposite sign (+1.00), new axis = 90° from old axis (045+90=135).
COT Optometry 3
A patient wearing +2.50 D lenses moves a held object away and the image appears to move in the same direction.
This is called: