4-18-2) accumulates in the epithelium at the base of the cone (Fleischer ring). 4-18-1), thinning of the corneal apex, scarring at the level of Bowman’s layer, and deep stromal stress lines that clear when pressure is applied to the globe. Manifestations of keratoconus include steepening of the cornea, espe-cially inferiorly (Fig. The mechanism by which eye rubbing contributes to kerato-conus is not completely understood, but may be related to mechanical epithelial trauma, triggering a wound-healing response that leads to keratocyte apoptosis. Other investigators have suggested that abnormalities in corneal collagen and its cross-linking may be the cause of keratoconus.7Įye rubbing is strongly associated with the development of kerato-conus. 5 Increased apoptosis of kerato-cytes has been observed.6 It is postulated that this loss of keratocytes results in a decrease in collagen and extracellular matrix production, leading to reduced stromal mass. Loss of stromal keratocytes has also been reported in keratoconus, as suggested by confocal microscopy. This is supported by multiple studies suggesting increased levels of degradative lysosomal enzymes and decreased levels of inhibi-tors of proteolytic enzymes in corneal epithelium.1,2 These findings are consistent with the observation of increased collagenolytic and gelati-nolytic activity in keratoconic cells.3,4 Ectasia can occur after any keratorefractive procedure but, for the sake of this chapter, we will be addressing only laser in situ keratomileusis (LASIK) and surface ablation.Keratoconus is a disorder characterized by progressive corneal steepen-ing, most typically inferior to the center of the cornea, with eventual corneal thinning, induced myopia, and both regular and irregular astigmatism.Ī hallmark of keratoconus is stromal thinning, which may be related to alterations in enzyme levels in the cornea, causing stromal degradation. Ectasia can be defined as progressive non-inflammatory corneal thinning after surgery resulting in irregular topographic steepening and resultant irregular astigmatism. The incidence of ectasia after refractive surgery is not known precisely, but has been estimated to be 0.2%–0.66% in two studies. Post-LASIK ectasia is a rare, but vision threatening complication. Moreover, it will be possible to help patients with advanced disease with stronger ICRS treatments and state of the art corneal lamellar surgery 3. With the advent of cross-linking, and perhaps with the combination of both modalities, the need for keratoplasty for keratoconus, which has an approximately 20% rejection rate, will decrease. Although long-term results with controlled studies are not known, depending on early results, ICRS not only provide better visual quality but also may help in controlling the progression of keratoconus 1, 2. This would allow more patients to be in the older ages when the progression of the keratoconus slows down, without significant complication and visual deprivation. In the future, controlling the progression of the disease will be another important goal for treatment modalities to achieve. The treatment of keratoconus, up to date, was mostly focused on visual rehabilitation. Keratoconus is a progressive disorder and usually its progression rate is higher before the fourth decade. Epidemiologic consideration and terminology
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