Contact Lens Fitting Flashcards
7 cards from real ABO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Contact Lens Fitting flashcards as text
Residual astigmatism with an RGP lens is BEST corrected by:
Answer: Using a back-surface toric RGP lens
Residual (lenticular) astigmatism uncorrected by the tear lens requires a toric RGP design, typically back-surface toric.
The Holladay-Prager formula and similar tools are used in contact lens practice primarily for:
Answer: Calculating vertex distance power conversion
Vertex distance power conversion formulas (like Holladay's) convert spectacle Rx to contact lens power, especially important above ±4.00 D.
A new soft lens wearer reports blurry vision that clears momentarily after blinking. The MOST likely cause is:
Answer: Lens dehydration or poor wettability
Post-blink clearing of blur suggests the tear film temporarily restores optical quality, pointing to lens dehydration or poor wettability.
Which of the following BEST describes 'limbal-to-limbal' fitting for a soft contact lens?
Answer: Lens diameter extends 1–2 mm beyond the HVID onto the sclera
Standard soft lenses are fit so their diameter extends approximately 1–2 mm beyond the limbus onto the sclera.
A contact lens patient shows 3 and 9 o'clock corneal staining with an RGP lens. This is MOST likely caused by:
Answer: Inadequate edge lift and poor tear meniscus at the lens periphery
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.
Extended wear (EW) contact lenses primarily require higher Dk/t values because:
Answer: Closed-eye oxygen tension is much lower, requiring higher transmissibility to prevent hypoxia
During sleep, the palpebral conjunctiva reduces corneal oxygen supply to ~8%, so lenses with very high Dk/t (≥87 for EW) are needed to prevent hypoxia.
Which lens material property is most important in reducing lipid deposit formation on contact lenses?
Answer: Ionic surface charge (FDA Group IV materials)
FDA Group IV lenses (high water, ionic) attract the most protein and lipid deposits due to their ionic surface charge.