ABO Contact Lenses 5

Question 1

A patient's spectacle Rx is -4.00 -2.00 x 180. Using the spherical equivalent, what power soft contact lens would you initially trial?

Accepted Answer

-5.00 D

Answer

Spherical equivalent = sphere + (cylinder/2) = -4.00 + (-2.00/2) = -4.00 + (-1.00) = -5.00 D.

Question 2

Which contact lens material property is described by the term 'wettability'?

Accepted Answer

The degree to which the lens surface attracts and retains the tear film

Answer

Wettability refers to how well the tear film spreads and adheres to the lens surface; poor wettability leads to dry spots, discomfort, and visual fluctuation.

Question 3

During slit-lamp evaluation of a newly fitted soft contact lens, what finding indicates the lens may be too tight?

Accepted Answer

Conjunctival blanching at the lens edge

Answer

Conjunctival blanching (vessel compression) at the lens edge indicates excessive tightness causing mechanical restriction of blood flow at the limbus.

Question 4

What is the recommended minimum central corneal clearance (vault) when fitting a scleral contact lens?

Accepted Answer

200–400 microns

Answer

A minimum central clearance of approximately 200 microns (some guidelines say 200–400 µm) is recommended at dispensing to account for settling over the wear period.

Question 5

A rigid contact lens has a Dk of 100 and a center thickness of 0.20 mm. What is its Dk/t value?

Accepted Answer

500

Answer

Dk/t = Dk ÷ thickness in cm = 100 ÷ 0.020 cm = 500 × 10⁻⁹ (Fatt units); dividing 100 by 0.02 gives 500.

ABO - American Board of Optometry Practice Test

ABO - American Board of Optometry Practice Test

ABO Contact Lenses 5