Neurotrophic keratitis
Neurotrophic keratitis (NK) is a degenerative disease of the cornea caused by damage of the trigeminal nerve[1], which results in impairment of corneal sensitivity, spontaneous corneal epithelium breakdown, poor corneal healing and development of corneal ulceration, melting and perforation[2].
Neurotrophic keratitis is classified as a rare disease, with an estimated prevalence of less than 5 in 10,000 people in Europe. It has been recorded that on average, 6% of herpetic keratitis cases may evolve to this disease, with a peak of 12.8% of cases of keratitis due to herpes zoster virus[3].
The diagnosis, and particularly the treatment of neurotrophic keratitis are the most complex and challenging aspects of this disease, as a satisfactory therapeutic approach is not yet available[4].
The cornea, an avascular tissue, is among the most densely innervated structures of the human body. Corneal nerves are responsible for maintaining the anatomical and functional integrity of the cornea, conveying tactile, temperature and pain sensations, playing a role in the blink reflex, in wound healing and in the production and secretion of tears[5].
Most corneal nerve fibres are sensory in origin and are derived from the ophthalmic branch of the trigeminal nerve[6]. Congenital or acquired ocular and systemic diseases[7] can determine a lesion at different levels of the trigeminal nerve, which can lead to a reduction (hypoesthesia) or loss (anesthesia) of sensitivity of the cornea[8].
The most common causes of loss of corneal sensitivity are viral infections (herpes simplex[9] and herpes zoster ophthalmicus[10]), chemical burns, physical injuries, corneal surgery, neurosurgery[11], chronic use of topical medications, or chronic use of contact lenses[12].
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