NOCE NOCE Contact Lens Fitting and Care 1 — Questions and Answers
Question 1: What does the base curve (BC) of a contact lens refer to?
- The thickness at the center of the lens
- The radius of curvature of the back surface of the lens (Correct answer)
- The total diameter of the lens
- The refractive power of the lens
Correct answer: The radius of curvature of the back surface of the lens
The base curve is the radius of curvature of the posterior (back) surface of a contact lens, typically measured in millimeters.
Question 2: What does the Dk value of a contact lens material represent?
- Lens durability and scratch resistance
- Oxygen permeability of the lens material (Correct answer)
- Refractive index of the lens
- Water content percentage
Correct answer: Oxygen permeability of the lens material
Dk is a measure of oxygen permeability where D is the diffusion coefficient and k is the solubility of oxygen in the lens material.
Question 3: What is the typical overall diameter range for standard soft contact lenses?
- 8.0–9.0 mm
- 9.5–10.5 mm
- 13.8–14.5 mm (Correct answer)
- 16.0–17.0 mm
Correct answer: 13.8–14.5 mm
Most soft contact lenses have an overall diameter of 13.8–14.5 mm to ensure proper corneal coverage and limbal overlap.
Question 4: Which FDA group classification describes soft contact lens materials with HIGH water content and IONIC charge?
- Group I
- Group II
- Group III
- Group IV (Correct answer)
Correct answer: Group IV
FDA Group IV contact lens materials are ionic (charged) with high water content (≥50%), making them more susceptible to deposits.
Question 5: What is the primary function of the pre-lens tear film in contact lens wear?
- To increase lens oxygen permeability
- To lubricate the lens surface and maintain optical clarity (Correct answer)
- To prevent lens dehydration permanently
- To sterilize the contact lens during wear
Correct answer: To lubricate the lens surface and maintain optical clarity
The pre-lens tear film provides lubrication, maintains a smooth optical surface over the contact lens, and supplies nutrients to the cornea.
Question 6: Daily disposable contact lenses are designed to be worn for what maximum duration before disposal?
- One hour per day
- One full day, then discarded (Correct answer)
- One week with nightly removal
- 30 days of continuous wear
Correct answer: One full day, then discarded
Daily disposable lenses are single-use lenses designed to be worn for one day and discarded each evening, eliminating the need for lens care solutions.
NOCE NOCE Contact Lens Fitting and Care 1
What does the base curve (BC) of a contact lens refer to?