Which measurement is essential when fitting a rigid gas permeable lens?

The base curve is a critical measurement when fitting a rigid gas permeable (RGP) lens because it directly affects how the lens will fit on the cornea. The base curve refers to the curvature of the back surface of the lens, which should align closely with the natural curvature of the wearer's cornea. An appropriate base curve ensures that the lens sits comfortably and remains stable on the eye, allowing for proper tear exchange beneath the lens.

If the base curve is too flat or too steep, it can lead to discomfort, inadequate vision correction, or issues with lens movement and positioning. Therefore, precise measurement of the base curve is essential to achieving an optimal fit, promoting the health of the eye, and maximizing visual acuity.

Other measurements, while important for overall fitting, do not have the same foundational impact on the lens’s relationship with the corneal surface as the base curve does.