The cornea lacks blood vessels and 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. Most corneal nerve fibres are sensory in origin and are derived from the ophthalmic branch of the trigeminal nerve. Congenital or acquired ocular and systemic diseases 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. The most common causes of loss of corneal sensitivity are viral infections (herpes simplex and herpes zoster ophthalmicus), chemical burns, physical injuries, corneal surgery, neurosurgery, chronic use of topical medications, or chronic use of contact lenses. Possible causes also include systemic diseases such as diabetes mellitus, multiple sclerosis or leprosy. Other, albeit less frequent, potential causes of the disease are: intracranial space-occupying lesions such as neuroma, meningioma and aneurysms, which may compress the trigeminal nerve and reduce corneal sensitivity. Conversely, congenital conditions that may lead to this disorder are very rare.
Neurotrophic keratitis
Nummular keratitis
Fungal keratitis
Peripheral ulcerative keratitis
Interstitial keratitis
Fuchs heterochromic iridocyclitis
Lattice corneal dystrophy
Subepithelial mucinous corneal dystrophy