ABO Contact Lens Fitting 3 — Questions and Answers
Question 1: What is the primary purpose of the edge lift in an RGP contact lens design?
- Increase oxygen permeability
- Allow tear exchange and lens movement (Correct answer)
- Reduce lens mass
- Improve optical clarity
Correct answer: Allow tear exchange and lens movement
Adequate edge lift creates a reservoir beneath the lens periphery, facilitating tear exchange and preventing lens adherence.
Question 2: A scleral lens is most indicated for which of the following conditions?
- Low myopia with regular astigmatism
- Severe dry eye with irregular corneal surface (Correct answer)
- Early-stage presbyopia
- Mild corneal warpage from soft lens wear
Correct answer: Severe dry eye with irregular corneal surface
Scleral lenses vault completely over the cornea and land on the sclera, providing a fluid reservoir that benefits both irregular corneas and severe dry eye.
Question 3: Which finding during a slit-lamp evaluation of a soft contact lens wearer suggests giant papillary conjunctivitis (GPC)?
- Inferior corneal staining in a smile pattern
- Papillae greater than 0.3 mm on the upper tarsal conjunctiva (Correct answer)
- Limbal hyperemia only
- Punctate epithelial erosions superiorly
Correct answer: Papillae greater than 0.3 mm on the upper tarsal conjunctiva
GPC is characterized by papillae ≥0.3 mm (often ≥1 mm in advanced cases) on the superior tarsal conjunctiva.
Question 4: When assessing soft contact lens fit, acceptable lens movement after a blink should be approximately:
- 0–0.1 mm
- 0.2–0.4 mm (Correct answer)
- 1.0–1.5 mm
- 2.0 mm or more
Correct answer: 0.2–0.4 mm
Optimal soft lens movement is 0.2–0.4 mm on primary gaze blink, indicating neither a too-tight nor too-loose fit.
Question 5: A patient wearing silicone hydrogel lenses develops superior epithelial arcuate lesions (SEALs). The most appropriate initial management is:
- Switch to a thicker, higher-Dk lens
- Refit with a flatter base curve or thinner lens (Correct answer)
- Prescribe topical steroids immediately
- Discontinue lens wear permanently
Correct answer: Refit with a flatter base curve or thinner lens
SEALs are caused by mechanical trauma from a stiff lens edge; refitting with a flatter base curve or thinner lens reduces this mechanical effect.
Question 6: What does the term 'sagittal depth' describe in contact lens fitting?
- The thickness of the lens at its center
- The vertical distance from the chord diameter to the back surface of the lens (Correct answer)
- The oxygen permeability of the lens material
- The refractive index of the lens
Correct answer: The vertical distance from the chord diameter to the back surface of the lens
Sagittal depth (sag) is the depth of the 'bowl' of the lens, determined by both base curve and diameter, and it dictates how the lens vaults the eye.
Question 7: Which corneal staining pattern is most characteristic of solution toxicity from contact lens care products?
- Superior arcuate staining
- Diffuse punctate epithelial staining across the entire cornea (Correct answer)
- 3 and 9 o'clock peripheral staining
- Central corneal staining only
Correct answer: Diffuse punctate epithelial staining across the entire cornea
Solution toxicity typically presents as diffuse superficial punctate keratitis spread across the entire corneal surface.
ABO Contact Lens Fitting 3
What is the primary purpose of the edge lift in an RGP contact lens design?