What does a flat fit in an RGP lens imply?

A flat fit in a rigid gas permeable (RGP) lens denotes that the lens is designed to rest on the cornea in a way that its central portion touches the corneal apex. This fit is essential for several reasons. When the lens touches the corneal apex, it allows for optimal tear exchange beneath the lens, providing comfort and improved visual function without causing excessive pressure or discomfort.

In fitting RGP lenses, achieving the right relationship between the lens and the cornea is critical. A flat fit may also indicate the proper alignment of the lens to the shape of the cornea, which can help maintain stability and prevent lens displacement during blinking or movement of the eye. Therefore, the correct understanding of a flat fit is that the lens is indeed making contact with the corneal apex, which is vital for effective vision correction and wearing comfort.