Neurotrophic Keratitis

Neurotrophic keratitis (NK) is a rare degenerative disease affecting the cornea (1).

The cornea is the most densely innervated tissue of the body (2). Sensory innervation of the cornea is derived from the first branch of the trigeminal nerve (2). In addition to serving as an afferent arm of the blink and tear reflex, sensory corneal nerves also provide trophic support to the corneal epithelium while facilitating and maintaining ocular surface homeostasis (3).

In patients with NK, the corneal sensory nerves are impaired leading to reduced corneal sensitivity and lack of trophic support to the corneal tissue (1, 4, 5). Without being able to sense external stimuli such as touch, wind, chemicals, light, heat and cold, the brain does not receive these critical signals to in turn respond with eyelid blinking and reflex tear production, which are protective for the corneal surface. Lack of these protective responses can cause the outer layer of the cornea, the epithelium, to thin and break down and cause an irregular surface distorting light and the tear film. As a result of the parallel lack of trophic support by corneal nerves, a detrimental loop is initiated, and the epithelial damage can progress to impairment of corneal healing (1, 5). In some cases, NK can progress and potentially lead to further damage such as ulceration and in severe cases perforation (1, 5).