Contact Lens Practice Flashcards

Scleral contact lenses differ from corneal RGP lenses primarily because they:

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.

Silicone hydrogel lenses have largely replaced conventional hydrogel lenses because they offer:

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.

Acanthamoeba keratitis is uniquely associated with which contact lens behavior?

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.

When fitting toric soft contact lenses, the lens should rotate to the:

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.

Which condition is a primary indication for fitting a patient with rigid gas-permeable lenses instead of soft lenses?

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.

Contact lens-induced corneal neovascularization is primarily caused by:

Answer: Chronic corneal hypoxia stimulating VEGF release

Sustained corneal hypoxia triggers VEGF upregulation, stimulating vessel growth from the limbus into the normally avascular cornea.