Kerataconus

Kerataconus is a condition where the cornea, the front surface of the eye, changes shape from being nice and spherical to becoming pointed or cone shaped.

This induces large amounts of astigmatism and very often myopia too. The cause of Kerataconus is unknown, it is believed to occur due to a combination of genetic, environmental, and hormonal factors. Another school of thought is that is is due to an imbalance in the enzymes in the eye.
Kerataconus is a progressive condition and requires a surgical intervention called corneal cross linking to help stabilze the cornea.

Depending on how advanced the condition is, visual correction, by either hard contact lenses or scleral contact lenses, is the method of choice.

Scleral lenses. These are large-diameter gas permeable contacts — large enough that the periphery and edge of the lens rest on the "white" of the eye (sclera). Scleral lenses cover a larger portion of the sclera, whereas semi-scleral lenses cover a smaller area.

Because the center of scleral and semi-scleral lenses vaults over the irregularly shaped cornea, these lenses don't apply pressure to the eye's cone-shaped surface for a more comfortable fit. These larger lenses also are more stable than conventional gas permeable contact lenses, which move with each blink because they cover only a portion of the cornea.