CPOT Contact Lens Fitting & Patient Care 1 — Questions and Answers
Question 1: Which contact lens material has the highest oxygen transmissibility (Dk/t)?
- PMMA (polymethylmethacrylate)
- Conventional hydrogel
- Silicone hydrogel (Correct answer)
- Low-water-content soft lens
Correct answer: Silicone hydrogel
Silicone hydrogel lenses allow significantly more oxygen to reach the cornea than conventional hydrogel or PMMA lenses because the silicone component is highly oxygen-permeable.
Question 2: Which contact lens design is used to correct astigmatism?
- Spherical soft lens
- Toric lens (Correct answer)
- Multifocal lens
- Monovision lens
Correct answer: Toric lens
Toric lenses have different powers in different meridians and include stabilization features to correct astigmatism by staying properly oriented on the eye.
Question 3: What does the measurement 'Dk/t' represent in contact lens specifications?
- Lens diameter-to-thickness ratio
- Oxygen transmissibility (Correct answer)
- Water content percentage
- Base curve radius
Correct answer: Oxygen transmissibility
Dk/t represents oxygen transmissibility, where Dk is the material's oxygen permeability and t is the lens center thickness; higher values mean more oxygen reaches the cornea.
Question 4: Which contact lens replacement schedule carries the lowest risk of deposit buildup?
- Annual replacement
- Monthly replacement
- Bi-weekly replacement
- Daily disposable (Correct answer)
Correct answer: Daily disposable
Daily disposable lenses are discarded after each use, eliminating the accumulation of protein, lipid, and calcium deposits that build up on reusable lenses over time.
Question 5: What is the base curve of a contact lens?
- The lens's refractive power in diopters
- The central posterior radius of curvature (Correct answer)
- The overall lens diameter in millimeters
- The water content of the lens material
Correct answer: The central posterior radius of curvature
The base curve is the radius of the central posterior (back) surface of the contact lens; it must closely match the corneal curvature to achieve an appropriate fit.
Question 6: Rigid gas-permeable (RGP) contact lenses are considered the primary contact lens option for which condition?
- Presbyopia in low-prescription patients
- Mild myopia with low astigmatism
- Keratoconus with irregular corneal shape (Correct answer)
- Dry eye syndrome with frequent lens dropout
Correct answer: Keratoconus with irregular corneal shape
RGP lenses are preferred for keratoconus because their rigid anterior surface creates a smooth optical interface over the irregular cornea, providing superior visual acuity.
Question 7: What is the primary clinical advantage of rigid gas-permeable (RGP) lenses over soft contact lenses?
- Greater initial comfort and immediate adaptation
- Superior oxygen transmissibility and optical clarity (Correct answer)
- Easier insertion and removal technique
- Wider availability in tinted and colored options
Correct answer: Superior oxygen transmissibility and optical clarity
RGP lenses offer excellent oxygen permeability and crisp optical clarity, particularly for patients with irregular astigmatism or high refractive errors where soft lenses underperform.
CPOT Contact Lens Fitting & Patient Care 1
Which contact lens material has the highest oxygen transmissibility (Dk/t)?