ABO Contact Lens Fitting 4

Question 1

Residual astigmatism with an RGP lens is BEST corrected by:

Accepted Answer

Using a back-surface toric RGP lens

Answer

Residual (lenticular) astigmatism uncorrected by the tear lens requires a toric RGP design, typically back-surface toric.

Question 2

The Holladay-Prager formula and similar tools are used in contact lens practice primarily for:

Accepted Answer

Calculating vertex distance power conversion

Answer

Vertex distance power conversion formulas (like Holladay's) convert spectacle Rx to contact lens power, especially important above ±4.00 D.

Question 3

A new soft lens wearer reports blurry vision that clears momentarily after blinking. The MOST likely cause is:

Accepted Answer

Lens dehydration or poor wettability

Answer

Post-blink clearing of blur suggests the tear film temporarily restores optical quality, pointing to lens dehydration or poor wettability.

Question 4

Which of the following BEST describes 'limbal-to-limbal' fitting for a soft contact lens?

Accepted Answer

Lens diameter extends 1–2 mm beyond the HVID onto the sclera

Answer

Standard soft lenses are fit so their diameter extends approximately 1–2 mm beyond the limbus onto the sclera.

Question 5

A contact lens patient shows 3 and 9 o'clock corneal staining with an RGP lens. This is MOST likely caused by:

Accepted Answer

Inadequate edge lift and poor tear meniscus at the lens periphery

Answer

Desiccation at the 3 and 9 o'clock positions occurs when the nasal and temporal tear meniscus is disrupted by a poorly designed lens edge.

ABO - American Board of Optometry Practice Test