Lenses Rigid gas permeable (RGP) lens In early stages of<unk> , glasses or soft contact lenses can suffice to correct for the mild astigmatism. As the condition progresses, these may no longer provide the person with a satisfactory degree of visual acuity, and most practitioners will move to manage the condition with rigid contact lenses, known as rigid, gas-permeable, (RGP) lenses. RGP lenses provide a good level of visual correction, but do not arrest progression of the condition. In people with<unk> , rigid contact lenses improve vision by means of tear fluid filling the gap between the irregular corneal surface and the smooth regular inner surface of the lens, thereby creating the effect of a smoother cornea. Many specialized types of contact lenses have been developed for<unk> , and affected people may seek out both doctors specialized in conditions of the cornea, and contact lens fitters who have experience managing people with<unk> . The irregular cone presents a challenge and the fitter will endeavor to produce a lens with the optimal contact, stability and steepness. Some trial-and-error fitting may prove necessary. Hybrid lenses Traditionally, contact lenses for<unk>  have been the 'hard' or RGP variety, although manufacturers have also produced specialized 'soft' or hydrophilic lenses and, most recently, silicone hydrogel lenses. A soft lens has a tendency to conform to the conical shape of the cornea, thus diminishing its effect. To counter this, hybrid lenses have been developed that are hard in the centre and encompassed by a soft skirt. However, soft or earlier generation hybrid lenses did not prove effective for every person. Early generation lenses have been discontinued. The fourth generation of hybrid lens technology has improved, giving more people an option that combines the comfort of a soft lens with the visual acuity of an RGP lens. Scleral lenses Scleral lens Scleral lenses are sometimes prescribed for cases of advanced or very irregular<unk> ; these lenses cover a greater proportion of the surface of the eye and hence can offer improved stability. Easier handling can find favor with people with reduced dexterity, such as the elderly. Piggybacking Some people find good vision correction and comfort with a "piggyback" lens combination, in which RGP lenses are worn over soft lenses, both providing a degree of vision correction. One form of piggyback lens makes use of a soft lens with a countersunk central area to accept the rigid lens. Fitting a piggyback lens combination requires experience on the part of the lens fitter, and tolerance on the part of the person with<unk> . Surgery Corneal transplant Corneal transplant for<unk> , approximately one week after surgery – multiple light reflections indicate folds in the cornea that later resolved Cornea transplant after one year of healing; two stitches are visible Between 11% and 27% of cases of<unk>  will progress to a point where vision correction is no longer possible, thinning of the cornea becomes excessive, or scarring as a result of contact lens wear causes problems of its own, and a corneal transplantation or penetrating keratoplasty becomes required.<unk>  is the most common grounds for conducting a penetrating keratoplasty, generally accounting for around a quarter of such procedures. The corneal transplant surgeon trephines a lenticule of corneal tissue and then grafts the donor cornea to the existing eye tissue, usually using a combination of running and individual sutures. The cornea does not have a direct blood supply, so the donor tissue is not required to be blood type matched. Eye banks check the donor corneas for any disease or cellular irregularities. The acute recovery period can take four to six weeks, and full postoperative vision stabilization often takes a year or more, but most transplants are very stable in the long term. The National<unk>  Foundation reports that penetrating keratoplasty has the most successful outcome of all transplant procedures, and when performed for<unk>  in an otherwise healthy eye, its success rate can be 95% or greater. The sutures used usually dissolve over a period of three to five years, but individual sutures can be removed during the healing process if they are causing irritation to the person. In the US, corneal transplants (also known as corneal grafts) for<unk>  are usually performed under sedation as outpatient surgery. In other countries, such as Australia and the UK, the operation is commonly performed with the person undergoing a general anaesthetic. All cases require a careful follow-up with an eye doctor (ophthalmologist or optometrist) for a number of years. Frequently, vision is greatly improved after the surgery, but even if the actual visual acuity does not improve, because the cornea is a more normal shape after the healing is completed, people can more easily be fitted with corrective lenses. Complications of corneal transplants are mostly related to vascularization of the corneal tissue and rejection of the donor cornea. Vision loss is very rare, though difficult-to-correct vision is possible. When rejection is severe, repeat transplants are often attempted, and are frequently successful.<unk>  will not normally reoccur in the transplanted cornea; incidences of this have been observed, but are usually attributed to incomplete excision of the original cornea or inadequate screening of the donor tissue. The long-term outlook for corneal transplants performed for<unk>  is usually favorable once the initial healing period is completed and a few years have elapsed without problems. One way of reducing the risk of rejection is to use a technique called deep anterior lamellar keratoplasty (DALK). In a DALK graft, only the outermost epithelium and the main bulk of the cornea, the stroma, are replaced; the person's rearmost endothelium layer and the Descemet's membrane are left, giving some additional structural integrity to the postgraft cornea. Furthermore, it is possible to transplant freeze-dried donor tissue. The freeze-drying process ensures this tissue is dead, so there is no chance of rejection. Research from two trials in Iran provide low to moderate evidence that graft rejection is more likely to occur in 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<unk> . 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 pair of Intacs after insertion into the cornea 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<unk> . 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<unk> . In 2016, however, the FDA approved cross-linking surgery as a treatment for<unk>  and recommended that a registry system should be set-up to evaluate the long-term treatment effect. The Save Sight<unk>  Registry is an international database of<unk>  patients that is tracking outcomes of cross-linking in patients with<unk> . Radial keratotomy Diagram of MARK incisions 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<unk>  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<unk> .
Keratoconus
Pellucid marginal degeneration
Pinguecula
Corpora arenacea
Epiblepharon
Ecamsule
Enamel pearl
Vitreous bulge