Does increasing the OZD of a CL lens result in a steeper or flatter fit?

Does increasing the OZD of a CL lens result in a steeper or flatter fit?

• A. Steeper
• B. Flatter
• C. No change
• D. Varies with lens type

Answer: (A)

When a contact lens sits on the eye, the fit is largely determined by sagittal height—the amount the lens curves from center to edge. Increasing the overall diameter while keeping the same base curve increases this sagittal height. That added curvature makes the lens bite more into the tear film and sit more tightly on the cornea, producing a steeper, tighter fit. So, expanding the optic zone/overall diameter tends to make the lens fit more steeply. The other options don’t fit because a larger diameter does change how the lens conforms to the eye (not no change), and it generally makes the fit steeper rather than flatter. While lens design can modulate exact behavior, the basic geometric effect of a larger diameter is an increased sagittal height, i.e., a steeper fit.

When a contact lens sits on the eye, the fit is largely determined by sagittal height—the amount the lens curves from center to edge. Increasing the overall diameter while keeping the same base curve increases this sagittal height. That added curvature makes the lens bite more into the tear film and sit more tightly on the cornea, producing a steeper, tighter fit. So, expanding the optic zone/overall diameter tends to make the lens fit more steeply.

The other options don’t fit because a larger diameter does change how the lens conforms to the eye (not no change), and it generally makes the fit steeper rather than flatter. While lens design can modulate exact behavior, the basic geometric effect of a larger diameter is an increased sagittal height, i.e., a steeper fit.