The advantage of DALK is even more evident in patients with mental retardation in which PK has a higher incidence of postoperative complications such as globe rupture, corneal ulceration and graft rejection, as well as in phakic patients, and corneas with significant peripheral thinning. In general, despite the excellent outcomes of PK, DALK may be preferred in patients with keratoconus because of the absence of risk of endothelial rejection, earlier tapering of steroids, decreased risk of secondary glaucoma, and increased wound strength. These techniques would permit penetrating keratoplasty (PK) or deep anterior lamellar keratoplasty (DALK) to be postponed or avoided entirely. ![]() These less troublesome therapeutic alternatives will seek to arrest disease progression, re-enable comfortable contact lens, or improve visual acuity to some extent, although rarely do the visual gains exceed one or two lines in advanced disease. In 2014, Bowman Layer transplantation was also described for advanced keratoconus with extreme thinning/steepening. Nevertheless, there has been a strong push to extend other treatment modalities that were originally meant for mild to moderate disease such as ultraviolet crosslinking (UV-CXL) and intrastromal corneal ring segments (ICRS) to treat advanced disease. Therefore, although there is no precise definition for advanced disease, most specialists would agree that a keratoconus patient is eligible for corneal transplant when spectacle correction is insufficient, continued contact lens wear is intolerable, and visual acuity has fallen to unacceptable levels. While there are eyes with milder disease that may exhibit contact lens intolerances, there are other eyes with severe disease that obtain good functional vision with contact lenses. All these different scales do not always correlate well with disease impact. ![]() There are many different grading schemes for keratoconus from scales based on outdated indices such as the Amsler-Krumeich scale, to scales using a variety of detailed metrics of corneal structure provided by anterior segment optical coherence tomography and Pentacam imaging. Corneal graft is the traditional recourse for advanced keratoconus.
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