Penetration depth of corneal cross‐linking with riboflavin and UV‐A (CXL) in horses and rabbits

Abstract

CXL penetration depth, as determined by a novel ex vivo fluorescent assay, shows clear differences between species. A distinct effect was observed following epithelium-off CXL treatment in the anterior stroma of rabbits, but no different effect was observed in horses in comparison with nontreated controls. Different protocols need to be established to effectively treat equine patients with infectious corneal disease.

Optimizing corneal riboflavin administration in ex vivo horse, dog, rabbit, and pig samples for use in corneal collagen cross‐linking

“…Therefore, several studies aimed at understanding and controlling CXL depth within the cornea have been described. 1,19 These studies identified species-specific differences in the depth of cross-linked corneal fibrils following CXL. However, it is not clear in these studies whether the limiting factor was UV light penetration or riboflavin penetration.…”

“…Currently, the most common method of riboflavin administration for CXL involves use of riboflavin solution applied as eyedrops to the cornea every 2-5 minutes for at least 30 minutes after the corneal epithelium has been removed. 1,3,[7][8][9][10]13,14,20 This technique is commonly referred to as the Dresden Protocol. 5 The epithelium is removed because epithelium is a substantial barrier to stromal riboflavin penetration.…”

“…5 The epithelium is removed because epithelium is a substantial barrier to stromal riboflavin penetration. 1,[3][4][5]7,11,19 While humans can self-administer these eye drops, when used in animals this drop administration protocol requires considerable time on the part of the veterinarian and their nursing staff. Moreover, applying eye drops in large animals such as horses can be very difficult.…”

“…21 This provides an efficient alternative to the Dresden protocol. 1,3,[7][8][9][10]13,14,20 However, there are significant interspecies differences in corneal epithelium and stromal thickness. [23][24][25] It is not clear whether iontophoresis could overcome the epithelial barrier in horses, or other species with thicker corneal epithelium, or reach the deeper corneal stroma in animals with a thicker cornea than rabbits.…”

Development of a novel ex vivo equine corneal model

“…Equine corneal research to date has typically been performed using either in vitro model systems or in vivo studies utilizing a low number of animals . In vitro models utilize monocultures of representative corneal cell populations and cannot fully evaluate potential pathologic and toxic changes that may occur in the multilayered cornea.…”