The central base curve should be steep enough to clear which anatomical landmark?

The central base curve should be steep enough to clear which anatomical landmark?

• A. corneal apex
• B. corneal limbus
• C. iris
• D. pupil

Answer: (A)

In gas-permeable lens fitting, the central base curve is chosen to align with the very center of the cornea without pressing on it. The corneal apex is the point of greatest curvature and elevation on the cornea, so ensuring there is clearance at this spot is essential for a comfortable, stable fit and clear vision. If the base curve weren’t shaped to clear the apex, the lens could bear on that central point, leading to lens-induced staining, pressure, and reduced visual quality. The corneal limbus sits at the edge where cornea meets sclera and is more about peripheral alignment than central clearance, while the iris and pupil are posterior to the cornea and lens and aren’t the reference points used to gauge central fit.

In gas-permeable lens fitting, the central base curve is chosen to align with the very center of the cornea without pressing on it. The corneal apex is the point of greatest curvature and elevation on the cornea, so ensuring there is clearance at this spot is essential for a comfortable, stable fit and clear vision. If the base curve weren’t shaped to clear the apex, the lens could bear on that central point, leading to lens-induced staining, pressure, and reduced visual quality. The corneal limbus sits at the edge where cornea meets sclera and is more about peripheral alignment than central clearance, while the iris and pupil are posterior to the cornea and lens and aren’t the reference points used to gauge central fit.