The lens design of an ortho-k lens is different from the standard RGP lens as it consists of a treatment curve or what is referred to as the base curve, a reverse curve where the lens allows room for the cornea to shift and reshape, the alignment or fitting curve, and the peripheral curve. The cornea is malleable in that if you apply pressure in one area, that shapeshifts and adds fullness in another area. If you think of a waterbed, the volume inside doesn’t change, but the shapeshifts are dependent on where the pressure is applied. Your treatment curve applies pressure to the cornea and the reverse curve acts as a mold, limiting the amount of shift of the cornea. The alignment or peripheral curve is important to the stability of the lens, ensuring that it stays in place.