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

Pupil size

Answer

Palpebral fissure width

Answer

Iris color

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

The contact lens material absorbs some light

Answer

The tear film adds plus power

Answer

Manufacturing tolerances require rounding

Question 3

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

Accepted Answer

Excessive movement and edge standoff

Answer

No movement with bubbles trapped underneath

Answer

Lens decentration inferiorly

Answer

Central bearing with peripheral touch

Question 4

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

Accepted Answer

Disinfectant (such as hydrogen peroxide or polyquaternium)

Answer

Surfactant cleaner

Answer

Wetting agent

Answer

Chelating agent

Question 5

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

Accepted Answer

Oxygen transmissibility through the lens

Answer

Lens diameter to thickness ratio

Answer

Lens curvature to power ratio

Answer

Moisture content percentage

Question 6

What is the recommended minimum Dk/t for extended (overnight) contact lens wear?

Accepted Answer

87 (Holden-Mertz criterion)

Answer

24

Answer

125

Answer

50