ABO Contact Lens Fitting

Question 1

What is the primary measurement needed before fitting rigid gas permeable (RGP) contact lenses?

Accepted Answer

Corneal curvature (keratometry readings)

Answer

Keratometry readings provide the corneal curvature measurements essential for selecting the initial base curve of an RGP lens.

Question 2

A contact lens prescription of -3.00 D corresponds to a spectacle prescription of -3.25 D at a 12mm vertex distance. Why is the contact lens power less minus?

Accepted Answer

The contact lens sits closer to the eye, requiring less minus power

Answer

When a minus lens moves closer to the eye (decreasing vertex distance), less minus power is needed because the effective power of the lens increases at shorter distances.

Question 3

What does a flat-fitting soft contact lens typically demonstrate on slit lamp evaluation?

Accepted Answer

Excessive movement and edge standoff

Answer

A flat-fitting soft lens has a base curve that is flatter than the cornea, causing excessive movement, poor centration, and visible edge standoff.

Question 4

Which contact lens care solution component is responsible for killing microorganisms?

Accepted Answer

Disinfectant (such as hydrogen peroxide or polyquaternium)

Answer

The disinfectant component, such as hydrogen peroxide or polyquaternium-1, is specifically designed to kill bacteria, fungi, and other microorganisms on the lens surface.

Question 5

What is the Dk/t value of a contact lens measuring?

Accepted Answer

Oxygen transmissibility through the lens

Answer

Dk/t measures oxygen transmissibility, where Dk is the oxygen permeability of the material and t is the lens thickness. Higher Dk/t values indicate more oxygen reaches the cornea.

ABO - American Board of Optometry Practice Test

ABO - American Board of Optometry Practice Test

ABO Contact Lens Fitting