What does the term "base curve" refer to in lens design?

The term "base curve" in lens design specifically refers to the primary curvature of the lens that influences how it conforms to the shape of the cornea. This curvature is crucial for achieving proper fit and alignment of the lens on the eye, which is essential for both comfort and optimal visual performance. A well-matched base curve helps in maintaining the lens's position on the eye, ensuring that it provides the correct optical correction and minimizes issues such as movement or discomfort. This concept is especially significant in fitting contact lenses, where the relationship between the lens surface and the cornea plays a vital role in the overall success of the lens wear.

The other options do not pertain to the definition of base curve. The color tint applied to the lens surface addresses different aspects of lens design related to aesthetics and UV protection, while the thickness of the lens edges pertains to the optical properties and weight of the lens rather than its curvature. The distance between the lens and the eye is relevant to fit and could involve aspects like vertex distance, but it does not define the base curve itself.