What optical characteristic is vital for fitting contact lenses properly?

The correct choice emphasizes corneal curvature as a vital optical characteristic for properly fitting contact lenses. The curvature of the cornea is critical because it determines how the contact lens will align and sit on the eye's surface. Each individual's cornea has a unique shape, impacting the fit and comfort of the lens. A well-fitted contact lens should match the curvature of the cornea to ensure optimal vision correction, comfort, and health of the eye.

When lenses do not properly align with the corneal curvature, it can lead to issues such as discomfort, blurred vision, and potential damage to the corneal surface, highlighting the importance of this characteristic in fitting contact lenses effectively.