When evaluating a gas permeable lens fit, which characteristic should be increased to improve movement?

Increasing the sagittal vault of a gas permeable lens can enhance lens movement because it creates additional space between the back surface of the lens and the cornea. This space allows the lens to move freely with the natural blinking action, which can improve comfort and provide better tear exchange underneath the lens. A higher sagittal vault helps in accommodating ocular changes, such as blinking and eye movements, thereby ensuring that the lens does not stick to the cornea and can maintain proper positioning.

In contrast, modifications such as increasing the lens diameter or altering the optic zone size do not directly influence the lens's movement relative to the cornea. While a larger diameter might initially sound like it would allow for more movement, it could lead to other fitting concerns and wouldn't necessarily promote additional movement in the way that adjusting the sagittal vault would. Additionally, adjusting the peripheral curve steepness mainly affects the lens's fitting characteristics at the edge and can have an influence on how the lens conforms to the shape of the eye, but it does not specifically increase movement under normal conditions.