AOA Contact Lens Practice 2 — Questions and Answers
Question 1: Scleral contact lenses differ from corneal RGP lenses primarily because they:
- Vault the entire cornea and rest on the sclera (Correct answer)
- Are softer and conform to the corneal shape
- Have higher water content than soft lenses
- Are designed for daily disposable use only
Correct answer: Vault the entire cornea and rest on the sclera
Scleral lenses have a large diameter (>18 mm) that vaults the cornea completely and lands on the scleral tissue, holding a fluid reservoir over the cornea.
Question 2: Silicone hydrogel lenses have largely replaced conventional hydrogel lenses because they offer:
- Higher oxygen permeability with similar or better comfort (Correct answer)
- Lower modulus of elasticity
- Greater resistance to lipid deposits
- Reduced UV exposure to the cornea
Correct answer: Higher oxygen permeability with similar or better comfort
Silicone hydrogel materials achieve Dk values 5–6× higher than conventional hydrogels, reducing hypoxic complications while maintaining wearable comfort.
Question 3: Acanthamoeba keratitis is uniquely associated with which contact lens behavior?
- Rinsing lenses with tap water or swimming while wearing lenses (Correct answer)
- Sleeping in daily disposable lenses
- Using expired lens care solutions
- Over-wearing annual replacement lenses
Correct answer: Rinsing lenses with tap water or swimming while wearing lenses
Acanthamoeba is a waterborne protozoan; exposure through tap water rinsing or water sports creates the primary risk for this difficult-to-treat corneal infection.
Question 4: When fitting toric soft contact lenses, the lens should rotate to the:
- Correct orientation as marked by the stabilization ballast (Correct answer)
- Superior limbus for maximum stability
- Nasal position regardless of the prescription
- Lower lid position to allow blink-driven rotation
Correct answer: Correct orientation as marked by the stabilization ballast
Toric lenses use prism ballast or peri-ballast stabilization to maintain axis orientation; correct on-eye position is verified by the lens markings aligning with the intended axis.
Question 5: Which condition is a primary indication for fitting a patient with rigid gas-permeable lenses instead of soft lenses?
- Keratoconus with irregular astigmatism (Correct answer)
- Low myopia with no astigmatism
- High water loss dry eye syndrome
- History of giant papillary conjunctivitis
Correct answer: Keratoconus with irregular astigmatism
RGP lenses mask irregular corneal surface and provide superior optical quality for keratoconus patients, unlike soft lenses that drape the irregular surface.
Question 6: Contact lens-induced corneal neovascularization is primarily caused by:
- Chronic corneal hypoxia stimulating VEGF release (Correct answer)
- Mechanical trauma from lens edge
- Solution sensitivity reaction
- Protein deposits on the lens surface
Correct answer: Chronic corneal hypoxia stimulating VEGF release
Sustained corneal hypoxia triggers VEGF upregulation, stimulating vessel growth from the limbus into the normally avascular cornea.
AOA Contact Lens Practice 2
Scleral contact lenses differ from corneal RGP lenses primarily because they: