The base curve radius will vary according to which two factors?

• A. Pupil size, eyelid height
• B. OAD, corneal astigmatism
• C. Corneal thickness, axial length
• D. Lens material, index

Answer: (B)

Base curve radius in a gas-permeable lens is about how the lens sits on the cornea and how it moves with the eyelids. The two main influences are the overall diameter (OAD) of the lens and the shape of the cornea, especially corneal astigmatism. A larger diameter increases the lens’s sagittal depth, which often means adjusting the base curve to keep the lens from bearing too much at the center or riding up at the edges. Corneal astigmatism means the cornea isn’t equally curved in all meridians, so the base curve may need to be steeper or flatter to maintain stable centration and comfortable movement across different meridians. Other factors like pupil size, eyelid height, corneal thickness, axial length, or lens material index don’t drive the base curve radius as directly, so the combination of OAD and corneal astigmatism best explains how the base curve radius is varied.