What is indicated by excessive lag in an RGP lens fitting?

Excessive lag in a rigid gas permeable (RGP) lens fitting is indicative of a flat fit. When an RGP lens is too flat for the curvature of the eye, it fails to adequately align with the corneal surface, resulting in increased movement or lag. This movement can be felt by the wearer, and during the fitting assessment, it becomes apparent when the lens moves excessively with blinking or eye movement. A proper fitting should result in a lens that mimics the eye’s contour closely, allowing for a more stable positioning with minimal lag.

In contrast, options describing a steep fit and tight fit refer to scenarios where the lens curves too aggressively around the cornea, leading to either excessive pressure on the eye or insufficient movement, which can also produce discomfort or blurred vision. Therefore, when faced with excessive lag, it’s clear that the issue stems from a lens that does not adequately match the corneal curvature, highlighting a flat fit.