If a gas permeable lens fits on the 'K' value, what is the lacrimal lens power?

When a gas permeable lens is fitted on the 'K' value, or the curvature of the cornea, it is designed to be placed in such a way that it aligns closely with the natural curvature of the cornea. The 'K' value represents the power of the cornea which is measured in diopters based on its curvature.

When the gas permeable lens is fitting correctly on the 'K' value, the lacrimal lens power—which refers to the power of the tear film layer between the lens and the cornea—is neutralized. This results in a plano power for the lacrimal lens, meaning that it neither adds to nor subtracts from the overall optical power of the system. Thus, the power of the lacrimal lens is effectively zero, indicating that the lens sits neutrally on the eye without changing the refractive power needed for clear vision.

In scenarios where the lens does not fit on the 'K' value properly, one might expect either a plus or minus power in the lacrimal lens, depending on how the lens aligns with the cornea. However, when it fits precisely on the 'K' value, this alignment creates a balance that results in plano power.