Rare degenerative corneal disease caused by an impairment of trigeminal corneal innervation, leading to a decrease or absence of corneal sensation.
Aetiology
Common causes of corneal anaesthesia:
- Viral infection (M/C): Herpes simplex and herpes zoster keratoconjunctivitis)
- Chemical burns
- Physical injuries
- Corneal surgery
Intracranial space-occupying lesions:
Compression of the trigeminal nerve/ganglion and produce an impairment of corneal sensitivity
- Neuroma
- Meningioma
- Aneurysms
Systemic diseases:
Decrease sensory nerve function or damage sensory fibres leading to corneal anaesthesia
- Diabetes
- Multiple sclerosis (MS)
- Leprosy
Pathophysiology
NK was initially described as “neuroparalytic keratitis” and experimentally demonstrated by Magendie, who hypothesized the presence of trophic nerve fibers in the trigeminal nerve regulating tissue metabolism. It is now demonstrated that the trigeminal nerve provides corneal sensation and also supplies trophic factors to the cornea, playing a key role in maintaining the anatomical integrity and function of the ocular surface. The ocular surface epithelium, tear gland, and sensory and autonomic nerve fibers exert a mutual influence of their structures and functions by the release of cytokines, neuropeptides, and neuromediators. Impairment of corneal trigeminal innervation causes morphological and metabolic epithelial disturbances and leads to development of recurrent or persistent epithelial defects.
Clinical features
Mackie classification:
- Stage I: Alterations of corneal epithelium (dry and opaque, with superficial punctate keratopathy and corneal oedema)
- Stage II: Epithelial defects (often in/near centre of cornea)
- Stage III: Corneal ulcers + stromal oedema and/or melting that may result in corneal perforation
Complications
- Corneal stromal melting
- Corneal perforation
Management
