A novel animal model of corneal neurotization in a Thy1-GFP+ rat: studying a novel solution to neurotrophic keratitis

Abstract

 

Purpose

 

Corneal anesthesia renders the cornea susceptible to occult injury leading to neurotrophic keratitis, progressive scarring and vision loss. Standard medical therapy often fails to prevent disease progression. New surgical techniques involving nerve transfers and grafts to reinnervate the cornea in humans has restored protective sensation and improved visual acuity. Establishing an animal model is necessary to investigate factors that mediate corneal nerve regrowth. Here we present a surgical model of corneal denervation in aThy1-GFP+ rat model, which can then be used to surgically reinnervate the cornea.

 

Methods

 

The Thy1-GFP+ rat strain expresses green fluorescent protein (GFP) in all neurons and axons, permitting reliable imaging of corneal nerves. A perilimbal incision was used to identify the ciliary nerves which were then transected lateral to the optic nerve and inferior to the lateral rectus muscle. Seven days following surgical denervation, confocal microscopy was used to image both the denervated cornea and contralateral intact cornea with a 10x objective.

 

Results

 

All rats tolerated the procedure well. Corneal nerve imaging in the Thy1-GFP+ rat strain with confocal microscopy permitted tracing of stromal, sub-basal and epithelial nerves within the cornea (Figure 1A). Seven days after injury and transection of the ciliary nerves, denervation was complete (Figure 1B).

 

Conclusions

 

Surgical corneal neurotization improves corneal sensation and ocular defense mechanisms, protecting vision in patients who would otherwise lose vision. We have demonstrated that the Thy1-GFP+ rat cornea can be effectively denervated through a minimally invasive intraocular approach and that corneal nerves can be reliably image with whole mount confocal microscopy. The Thy1-GFP+ rat can serve as the basis for a model to investigate corneal nerve regrowth following surgical neurotization, permitting the investigation and identification of treatments that may further potentiate nerve regrowth and improve clinical results.  

 

Figure 1. (A) GFP+ expression allows reliable tracing of corneal nerves with confocal imaging. (B) 7 days following transection there is complete loss of axons. Dotted lines indicate the periphery of the sample. (Note: cornea has been cut in four locations to enable imaging in one focal plane).