Neurotrophic Keratopathy

Neurotrophic keratopathy (NK) is a degenerative corneal disease caused by impairment of trigeminal sensory innervation. The cornea is the most densely innervated tissue in the body — its sensory nerves provide not only the afferent limb of the blink reflex but also trophic support essential for epithelial maintenance and healing. Loss of this innervation produces a characteristic cascade: reduced blink rate, impaired epithelial healing, persistent epithelial defects, and risk of progressive stromal ulceration and perforation. NK is classified by the Mackie staging system (Stage 1: epithelial changes; Stage 2: persistent epithelial defect; Stage 3: stromal ulceration).

NK is rare, with an estimated prevalence of less than 5 per 10,000. However, subclinical corneal hypoesthesia — which may progress to NK — is far more common, occurring in patients with herpes simplex keratitis, herpes zoster ophthalmicus, diabetes, and following corneal surgery.

Corneal sensory nerves (branches of the ophthalmic division of CN V) provide trophic factors — including substance P and insulin-like growth factor — that are essential for epithelial cell proliferation, migration, and adhesion. Loss of these trophic signals impairs epithelial healing, reduces goblet cell density, and disrupts the epithelial basement membrane. The reduced blink reflex allows desiccation and mechanical trauma to the exposed surface. Nerve growth factor (NGF) is a key trophic mediator — its deficiency is the target of cenegermin (Oxervate®) therapy.

Paradoxically, patients with NK often have minimal symptoms despite significant corneal pathology — reduced sensation blunts the normal pain response. Reduced or absent corneal sensation (tested with a cotton wisp or esthesiometer) is the hallmark finding. Stage 1 presents with superficial punctate keratopathy and epithelial irregularity. Stage 2 presents with a persistent epithelial defect (PED) — a non-healing corneal erosion with smooth, rolled edges. Stage 3 presents with stromal ulceration, melting, and risk of perforation.

Management is stepwise based on Mackie stage. Stage 1: preservative-free lubricants, elimination of toxic topical medications, and treatment of underlying cause. Stage 2 (PED): cenegermin (Oxervate® 0.002%) six times daily for 8 weeks — the first FDA-approved therapy targeting the neurogenic deficit; autologous serum tears; bandage contact lens; amniotic membrane. Stage 3 (stromal ulceration): all Stage 2 measures plus tarsorrhaphy (temporary or permanent) to reduce exposure; urgent referral for surgical management if perforation is threatened.

Monitor corneal sensation, epithelial integrity, and stromal thickness at each visit. Stage 2 and 3 patients require frequent follow-up (weekly or more) until the epithelial defect heals. Esthesiometry provides objective monitoring of sensory recovery.