Which statement about GP base curve radius is true?

• A. It varies with OAD and corneal astigmatism
• B. It is fixed
• C. It depends on age only
• D. It depends on color perception

Answer: (A)

GP base curve radius is chosen to match how the cornea actually sits under the lens and how the lens will sit across the chosen overall diameter. The cornea’s curvature isn’t constant: a steeper, more curved cornea needs a steeper base curve (smaller radius) so the lens centers well and maintains a stable tear film with comfortable movement. When corneal astigmatism is present, the curvature differs in meridians, so fitting often involves adjusting the base curve or using a multi-curve/toric design to achieve proper alignment across the meridians. The overall diameter also influences how the lens interacts with the eyelids and tears, which can lead to adjustments in the base curve choice. So, the base curve radius varies with both the intended overall diameter and the corneal astigmatism. The other statements aren’t correct because the base curve isn’t fixed, it isn’t determined by age, and color perception has no impact on GP lens fitting.