Decreasing the optic zone diameter leads to a flatter lens fit:

Decreasing the optic zone diameter leads to a flatter lens fit:

• A. Increasing
• B. Decreasing
• C. No change
• D. Depends on iris size

Answer: (B)

Fitting a gas permeable lens relies on how much of the lens’s central curvature is in contact with the cornea versus how much is governed by the peripheral zones. The optic zone is that central area that defines the main curvature over the cornea. If you decrease the optic zone diameter, the central curvature affects a smaller portion of the lens, so the flatter peripheral curves become more influential in the overall shape of the lens on the eye. This shift reduces the sag the eye would see from the lens, resulting in a flatter, less steep fit. Conversely, increasing the optic zone diameter would extend the central curvature over more of the lens, increasing sag and yielding a steeper fit. The effect isn’t dependent on iris size.

Fitting a gas permeable lens relies on how much of the lens’s central curvature is in contact with the cornea versus how much is governed by the peripheral zones. The optic zone is that central area that defines the main curvature over the cornea. If you decrease the optic zone diameter, the central curvature affects a smaller portion of the lens, so the flatter peripheral curves become more influential in the overall shape of the lens on the eye. This shift reduces the sag the eye would see from the lens, resulting in a flatter, less steep fit.

Conversely, increasing the optic zone diameter would extend the central curvature over more of the lens, increasing sag and yielding a steeper fit. The effect isn’t dependent on iris size.