NOCE NOCE Contact Lens Fitting and Care 1

Question 1

What does the base curve (BC) of a contact lens refer to?

Accepted Answer

The radius of curvature of the back surface of the lens

Answer

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?

Accepted Answer

Oxygen permeability of the lens material

Answer

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?

Accepted Answer

13.8–14.5 mm

Answer

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?

Accepted Answer

Group IV

Answer

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?

Accepted Answer

To lubricate the lens surface and maintain optical clarity

Answer

The pre-lens tear film provides lubrication, maintains a smooth optical surface over the contact lens, and supplies nutrients to the cornea.

NOCE - National Opticianry Competency Examination Practice Test