penetrating keratoplasty than in DALK, though the likelihood for graft failure were similar with both procedures. Epikeratophakia Rarely, a nonpenetrating keratoplasty known as an epikeratophakia (or epikeratoplasty) may be performed in cases of keratoconus. The corneal epithelium is removed and a lenticule of donor cornea is grafted on top of it. The procedure requires a greater level of skill on the part of the surgeon, and is less frequently performed than a penetrating keratoplasty, as the outcome is generally less favorable. However, it may be seen as an option in a number of cases, particularly for young people. Corneal ring implants A possible surgical alternative to corneal transplant is the insertion of intrastromal corneal ring segments. A small incision is made in the periphery of the cornea and two thin arcs of polymethyl methacrylate are slid between the layers of the stroma on either side of the pupil before the incision is closed by a suture. The segments push out against the curvature of the cornea, flattening the peak of the cone and returning it to a more natural shape. The procedure offers the benefit of being reversible and even potentially exchangeable as it involves no removal of eye tissue. Corneal intrastromal implantation surgery involving the implantation of a full ring is also available as a treatment option for keratoconus. Evidence supports that the full-ring implant improves vision outcomes for at least a year. Cross-linking Corneal collagen cross-linking is a developing treatment that aims to strengthen the cornea, however, according to a 2015 Cochrane review, there is insufficient evidence to determine if it is useful in keratoconus. In 2016, however, the FDA approved cross-linking surgery as a treatment for keratoconus and recommended that a registry system should be set-up to evaluate the long-term treatment effect. The Save Sight Keratoconus Registry is an international database of keratoconus patients that is tracking outcomes of cross-linking in patients with keratoconus. Radial keratotomy Radial keratotomy is a refractive surgery procedure where the surgeon makes a spoke-like pattern of incisions into the cornea to modify its shape. This early surgical option for myopia has been largely superseded by LASIK and other similar procedures. LASIK is absolutely contraindicated in keratoconus and other corneal thinning conditions as removal of corneal stromal tissue will further damage an already thin and weak cornea. For similar reasons, radial keratotomy has also generally not been used for people with keratoconus. Prognosis