Though both FDA approved, corneal refractive therapy [CRT for short] and orthokeratology [Ortho-k for short] aren't the same product and don't give the same guarantees. Both manufacturers use gas permeable materials for their lenses and both do reshape and flatten the cornea. All of the CRT's cornea-reshaping products are made by the company and no other brands sell or manufacture them. They are approved by the FDA, use only their own proprietary technology and are fit by that company's certified practitioners. Ortho-k, on the other hand, is manufactured and distributed by a variety of lens brands and designs and only one brand of ortho-k lenses is currently FDA approved for overnight wear. The ortho-k FDA approval is for up to five diopters of myopia- unlike CRT, which is approved for use by people with up to six diopters of myopia (-6.00 on your prescription).