Gas Permeable Contact Lenses – Lens Anatomy, Verification, And Selection Practice Test

The outer boundary of a GP lens is defined by where the central optical zone ends and the peripheral/landing zone begins. The parameter that directly controls that boundary is the optical zone diameter. By setting the optical zone diameter, you fix where the edge boundary sits across the lens, which matters for how the lens centers on the cornea and how the tear film interacts at the edge. Center thickness affects only how thick the lens is at the center, not where the boundary between optical and peripheral zones lies. Overall diameter determines the overall size of the lens but not the location of the boundary between zones. The physical edge describes the edge profile itself, but the specific boundary location is set by the optical zone diameter, making it the direct factor in defining that outer boundary.