COA Contact Lens Fundamentals

Question 1

What does the base curve of a contact lens describe?

Accepted Answer

The curvature of the central posterior surface of the lens

Answer

The base curve describes the radius of curvature of the central posterior (back) surface of the contact lens, which determines how the lens fits against the cornea.

Question 2

What does 'Dk' represent in contact lens terminology?

Accepted Answer

The oxygen permeability of the lens material

Answer

Dk is the oxygen permeability of a contact lens material, where D is the diffusion coefficient and k is the solubility coefficient of oxygen in the material.

Question 3

A patient's contact lens shows a tight-fitting pattern on fluorescein evaluation with a rigid gas-permeable lens. Which of the following best describes this fit?

Accepted Answer

Steep fit with central pooling and minimal edge clearance

Answer

A steep (tight) RGP fit shows central pooling of fluorescein under the center of the lens and reduced edge lift, indicating the lens curves more steeply than the cornea.

Question 4

Which type of contact lens is most appropriate for correcting irregular astigmatism caused by keratoconus?

Accepted Answer

Rigid gas-permeable lens

Answer

Rigid gas-permeable (RGP) lenses vault over the irregular corneal surface and use the tear lens to neutralize irregular astigmatism, making them the preferred option for keratoconus.

Question 5

What is the term for the measurement of the contact lens that describes its total width from edge to edge?

Accepted Answer

Overall diameter (OAD)

Answer

The overall diameter (OAD) refers to the total width of the contact lens measured from one edge to the other, and it is a key parameter in contact lens fitting.

COA - Certified Ophthalmic Assistant Practice Test

COA - Certified Ophthalmic Assistant Practice Test

COA Contact Lens Fundamentals