The first generation Ortho-K lenses are regular RGP or PMMA lenses. It is a custom spherical design fit 0.5-1.0D flatter than the corneal flattest K. This procedure needs multiple lenses changes in the course of one to two years and is able to reduce 1.00D of myopia. It is still good for the myopia control in teenage.
The second generation Ortho-K lenses are revolutionary designs which came out years ago. The outer zones of the lenses are steeper than the central zone. These designs are contrary to the corneal anatomy and named “Reverse Geometry” lenses that also need multiple lenses changes in the course of 6-12 months. These designs are able to reduce 1 - 3 Diopters of myopia. These lenses designs are still good for myopia control and high corneal astigmatism.
Example of second generation Ortho-K lenses:
Bridge Lens and 3D Lens from E & E Optics
The third generation Ortho-K lenses are breakthrough designs, which were dramatically different from lenses of the previous generations. The lenses are made of several different reverse curves. One lens might consist of five or more different curves. The patients might need to wear the lenses for 8-10 hours and have a functional vision for the rest of the day. For Myopia up to -5.00D, the first lens is the final lens in most cases.
Examples of the third generation Ortho-K lenses: