Abstract
Corneal cross-linking (CXL) is a surgical procedure able to modify corneal biomechanics and stabilize keratoconus progression. Although it is known that CXL produces changes in corneal collagen distribution, these are still a topic of discussion. Here we quantitatively compare the corneal stroma architecture between two animal models four weeks after in vivo conventional CXL treatment, with second harmonic generation (SHG) imaging microscopy and the structure tensor (ST). The healing stage and the stroma recovery were also analyzed by means of histological sections. Results show that the CXL effects depend on the initial arrangement of the corneal collagen. While the treatment increases the order in corneas with a low level of initial organization, corneas presenting a fairly regular pattern are hardly affected. Histological samples showed active keratocytes in anterior and middle stroma, what means that the recovery is still in progress. The combination of SHG imaging and the ST is able to objectively discriminate the changes suffered by the collagen arrangement after the CXL treatment, whose effectiveness depends on the initial organization of the collagen fibers within the corneal stroma.
Highlights
Collagen cross-linking (CXL) is a minimally invasive technique based on a photochemical reaction carried out by a photosensitizer exposed to ultraviolet A light (UVA, 370 nm)
We have investigated the performance of a standard CXL treatment in two animal models and the ability of second harmonic generation (SHG) imaging microscopy to detect changes produced in the corneal stroma four weeks after the in vivo treatment
Some authors compared the effects of using riboflavin alone or irradiating UVA without riboflavin instillation on the corneal stroma by analyzing TPEF signals [23, 43,44,45]
Summary
Collagen cross-linking (CXL) is a minimally invasive technique based on a photochemical reaction carried out by a photosensitizer (riboflavin, vitamin B2) exposed to ultraviolet A light (UVA, 370 nm). During this operation, reactive oxygen species are produced, which induces covalent bonds [1] between collagen fibrils and fibers, and between collagen and proteoglycans [2]. CXL has been reported to increase stromal stiffness [3, 4] and to be one of the most used clinical procedures to treat ectasias and halt keratoconus progression [3, 5, 6]. While some authors reported no progression during the follow-up [9, 10], others reported different failure rates [13,14,15]
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