What adjustment can be made to loosen a tightly-fitting gas-permeable lens?

To address the issue of a tightly-fitting gas-permeable lens, reducing the size of the optic zone is an effective adjustment. When the optic zone of a lens is made smaller, it generally allows for more movement of the lens on the cornea. This can enhance comfort for the wearer as it can prevent excessive pressure on the corneal surface, leading to a more relaxed fitting of the lens.

A smaller optic zone means that the lens will have a larger area of the lens that can vault over the cornea, thus allowing for greater tear exchange and preventing issues such as lens binding or discomfort due to tightness.

In contrast, steepening the base curve, increasing the overall diameter, or steepening the peripheral curve system would typically result in a tighter fit of the lens rather than a looser one. These adjustments would take the lens closer to the natural contours of the cornea, which is not ideal for a lens that is already fitting too tightly. Therefore, reducing the size of the optic zone is the most relevant option for loosening a gas-permeable lens fitting.