ChaseABC treated cornea crosslinked without having collagen, (E) ChaseABC taken care of cornea crosslinked with collagen.Values denote indicate regular deviation p<0.05 compared with the Control corneas p<0.05 compared with the COLG cornea ^p<0.05 compared with the ChaseABC corneas spacing and significantly decreased fibril density. Crosslinking with or without soluble collagen resulted in a significantly decrease of interfibrillar spacing, and an increase of fibril diameter and density.The DSC thermograms highlighted the matrix thermal stability changes after enzyme treatments (Fig 5). All samples presented one peak, which related to the temperature of thermal denaturation of collagen. After degradation, the transit temperature of COLG group and the ChaseABC group shifted to the lower temperature range (Table 3). After UVA crosslinking (with or without soluble collagen), the transition temperature increased as compared to the corneas with the same treatment.Keratoconus is a disease that can cause serious vision loss and necessitate corneal transplantation as it progresses. UVA crosslinking provides an approach to slow or even halt the progression of keratoconus, and restore vision [23]. However, there have been reports of complications with the UVA crosslinking approach, including stromal scaring [24,25], endothelial cell loss [26], and corneal melting [27,28]. The complication rate of crosslinking, defined as the percentage of eyes losing two or more Snellen lines, is 2.9% the failure rate (percentage of eyes with continued progression), by contrast, is 7.6% [29], which indicates that the crosslinking approach needs optimization to avoid failure and complications. Unfortunately, owing to the lack of readily available ex vivo tissue models of keratoconus, systematical studies of mechanisms and potential improvements of UVA crosslinking have been difficult. The main clinical feature of keratoconus is thinning and ectasia of the cornea [21,29,30]. These features have usually been associated with the degradation of the extracellular matrix caused by abnormal matrix metalloproteinase activity [31,32]. Enzymatic malfunction may relate to the ultrastructural change of collagen fibrils[33], decreases in corneal mechanical strength [34,35] and the characteristic cone-shaped textures [368]. In this study, we developed an ex vivo rabbit corneal ectatic model that mimics aspects of keratoconus. Rabbit is the most commonly used animal for corneal research [39]. Although rabbit corneas don't have the thin (812 m)Fig 5. Differential scanning calorimetry thermograms of ectatic corneas before and20171952 after crosslinking.Bowman’s layer that is found in human corneas [40], they are suited for ophthalmological research for several Sunset Yellow FCF reasons. 
Rabbit corneas have similar size, curvature and comparable stromal thickness to human corneas [41].
