Gas Permeable Contact Lenses Introduction Practice Test 2026 - Free Practice Questions and Study Guide

Surface wettability is the property that describes how a liquid interacts with a solid surface, and it’s quantified by the wetting or contact angle. The contact angle is the angle formed at the edge where the liquid, air, and solid meet, usually measured through the liquid. A smaller angle means the liquid spreads more easily over the surface, indicating good wettability; a larger angle means poorer spreading, or reduced wettability. In gas permeable contact lenses, higher wettability helps tears spread evenly over the lens, promoting comfort and tear film stability.

The other terms don’t describe this interaction: surface roughness relates to texture, not the angle of contact; refractive index is about how light bends at interfaces; color is about light absorption and reflection and is not a measure of liquid spreading on a surface.