COT Optometry 5 — Questions and Answers
Question 1: Which contact lens parameter describes the curvature of the back surface of the lens and determines how it fits on the cornea?
- Optical zone diameter
- Base curve radius (Correct answer)
- Center thickness
- Sagittal depth
Correct answer: Base curve radius
The base curve radius (BCR) defines the curvature of the posterior contact lens surface and is matched to corneal curvature for proper fit.
Question 2: A rigid gas-permeable (RGP) contact lens that is fit too steeply compared to the cornea will show which fluorescein pattern?
- Alignment pattern with uniform green ring
- Apical clearance (bull's-eye pattern) (Correct answer)
- Apical touch with peripheral pooling
- No fluorescein pooling anywhere
Correct answer: Apical clearance (bull's-eye pattern)
A steep-fitting RGP shows central fluorescein pooling (apical clearance) with peripheral edge seal, creating a bull's-eye appearance.
Question 3: The Snellen fraction 20/40 means the patient sees at 20 feet what a person with normal vision sees at:
- 10 feet
- 20 feet
- 40 feet (Correct answer)
- 80 feet
Correct answer: 40 feet
The denominator in a Snellen fraction represents the distance at which a normal observer can resolve the same letter the patient resolves at the test distance (20 feet).
Question 4: A patient with 20/20 acuity complains of glare and halos at night after LASIK. These symptoms are most likely caused by:
- Residual refractive error
- Ablation zone smaller than scotopic pupil diameter (Correct answer)
- Posterior capsule opacification
- Increased IOP
Correct answer: Ablation zone smaller than scotopic pupil diameter
When the scotopic (night) pupil dilates beyond the laser ablation zone, untreated peripheral cornea causes optical aberrations including halos and glare.
Question 5: Which type of bifocal segment provides the widest near reading area?
- Round segment (22 mm)
- Flat-top 28 segment
- Executive (full-width) bifocal (Correct answer)
- Blended bifocal
Correct answer: Executive (full-width) bifocal
The executive (Franklin-style) bifocal occupies the full width of the lens, providing the largest near viewing area of any bifocal segment design.
Question 6: When prescribing prism for a patient with esophoria, the base direction should be:
- Base-in
- Base-out (Correct answer)
- Base-up
- Base-down
Correct answer: Base-out
Base-out prism displaces images nasally, reducing the convergence demand and relieving the inward deviation of esophoria.
Question 7: A lensometer (lensmeter) is used to measure all of the following EXCEPT:
- Sphere power
- Cylinder power and axis
- Prism amount and direction
- Axial length of the eye (Correct answer)
Correct answer: Axial length of the eye
A lensometer measures the optical properties of ophthalmic lenses (sphere, cylinder, axis, prism); axial length is measured by A-scan ultrasound or optical biometry.
COT Optometry 5
Which contact lens parameter describes the curvature of the back surface of the lens and determines how it fits on the cornea?