Abstract
Since the late 1990s corneal crosslinking (CXL) has been proposed as a new possibility to stop progression of keratoconus or secondary corneal ectasia, with the promising aim to prevent progressive visual loss due to the evolution of the pathology and to delay or avoid invasive surgical procedures such as corneal transplantation. The possibility of strengthening corneal tissue by means of a photochemical reaction of corneal collagen by the combined action of Riboflavin and ultraviolet A irradiation (UVA), radically modified the conservative management of progressive corneal ectasia. This is a review of the state of the art of CXL, reporting basic and clinical evidence. The paper describes basic principles, advantages and limits of different CXL techniques and possible future evolution of the procedure.
Highlights
Corneal ectasia is a progressive corneal thinning associated with alterations of stromal collagen matrix resulting in irregular protrusion of the cornea
Post LASIK ectasia represents about 96 % of all secondary ectasias after refractive surgery, while 4 % are related to photorefractive keratectomy (PRK) surgery [6]
Keratoconus generally starts during the second decade of life with a variable rate of progression of corneal steepening that continues until the fourth decade, when the corneal shape generally becomes stable [7]
Summary
Corneal ectasia is a progressive corneal thinning associated with alterations of stromal collagen matrix resulting in irregular protrusion of the cornea. During the second anaerobic phase, when oxygen is depleted, corneal stroma interacts with reactive species of radical ions This photochemical reaction results in an increase of corneal rigidity, of collagen fiber thickness and of resistance to enzymatic degradation, with consequent decrease of stromal swelling and permeability maximally, above all in the anterior stroma [12]. In the last few years, several prospective and retrospective studies with a considerable follow-up period documented the effectiveness of the standard procedure in halting the progression of primary and secondary corneal ectasia, and in many cases, with an improvement of visual performance and topographical indexes. An in vivo confocal microscopy study reported that by increasing the duration of riboflavin application up to two hours, the obtained depth of CXL effect is similar to that achieved with standard epi-off technique [80]. Comparative studies of the effectiveness of the different CXL procedures are described in Table 5 [106,107,108,109,110,111,112,113,114,115]
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