Which action would tighten the fit of a contact lens?

Steepening the posterior curve of a contact lens is an effective way to tighten the fit. When the curvature of the posterior surface is made steeper, it increases the curvature of the lens that sits against the corneal surface. This tighter fit can enhance stability and comfort for the wearer, particularly if the lens is too loose or has been positioned incorrectly.

As the lens fits more snugly against the eye, it reduces movement on blinking and helps maintain proper alignment on the cornea, which is crucial for optimal vision and wearability.

The other actions, such as widening the peripheral curves or increasing the total diameter of the lens, would typically lead to a looser fit, as they would allow for more space around the lens, potentially leading to instability and discomfort. Similarly, using a thicker lens material alone does not inherently tighten the fit; it may change the overall weight and feel of the lens but does not affect how closely the lens conforms to the eye's shape.