Neurotrophic Keratitis

Excerpt

Neurotrophic keratitis is a degenerative corneal disease caused by impaired sensory innervation. The condition is characterized by decreased or absent corneal sensation, leading to epithelial breakdown, delayed healing, and, ultimately, corneal ulceration, melting, and perforation. Initially described as neuroparalytic keratitis, this corneal pathology was first demonstrated experimentally by Magendie in 1824.

Neurotrophic keratitis is a rare but vision-threatening disease that progresses due to corneal nerve dysfunction. The corneal nerves play a crucial role in maintaining ocular surface health by regulating epithelial cell proliferation, tear film stability, and immune responses. When these nerves are compromised by systemic or local conditions, the cornea loses its protective mechanisms, making it vulnerable to ulceration, infection, and mechanical trauma.

The prevalence of neurotrophic keratitis is relatively low, affecting approximately 5 per 10,000 individuals, but it is often underdiagnosed due to its subtle clinical presentation. The disease follows the 3-stage Mackie classification. Stage 1 is characterized by corneal epithelial irregularities and punctate keratopathy. Stage 2 presents with a persistent epithelial defect (PED) and stromal involvement. Stage 3 encompasses corneal ulceration with stromal melting and possible perforation.

Progression is often insidious, with patients rarely reporting pain due to diminished corneal sensation. However, some individuals may experience blurred vision, mild redness, or recurrent ocular surface inflammation. Early recognition and prompt intervention are essential to prevent irreversible damage and vision loss.

Neurotrophic keratitis results from damage to the sensory (afferent) fibers of the trigeminal nerve, the 5th cranial nerve. These fibers maintain corneal sensation and epithelial integrity. Several systemic and ocular conditions can lead to corneal nerve dysfunction, including herpetic infection from herpes simplex (HSV) or varicella-zoster (VZV) virus, diabetes mellitus, postsurgical nerve damage from procedures such as refractive surgery, corneal transplantation, or trigeminal neuralgia surgery, as well as chemical burns, chronic topical drug use, contact lens wear, and autoimmune diseases such as Sjögren syndrome.

Central nervous system disorders affecting the trigeminal ganglion or brainstem can also disrupt corneal innervation, contributing to neurotrophic keratitis. The corneal epithelium relies on trophic factors from corneal nerves, including substance P, nerve growth factor (NGF), and insulin-like growth factor 1 (IGF-1), to maintain ocular surface health and prevent epithelial breakdown. Loss of nerve function slows epithelial turnover, disrupts tear film dynamics, and impairs corneal healing, producing PEDs, ulceration, and corneal thinning. The absence of sensory feedback further reduces reflex tearing and blinking, exacerbating ocular surface desiccation and inflammation.

One of the most challenging aspects of diagnosing neurotrophic keratitis is the lack of significant symptoms despite ongoing corneal damage. Unlike other corneal diseases, where pain and discomfort prompt early medical attention, neurotrophic keratitis often remains undetected until severe complications arise. Common clinical signs include punctate epithelial erosions, PEDs, corneal ulceration, and thinning. In advanced cases, stromal necrosis and perforation may develop, necessitating urgent surgical intervention.

A comprehensive clinical evaluation should include corneal sensation testing with a cotton wisp, a Cochet-Bonnet esthesiometer, or dental floss. A slit-lamp examination can assess epithelial irregularities, tear meniscus height reduction, punctate keratopathy, and stromal opacities. Fluorescein and Rose Bengal staining help detect epithelial damage and conjunctival involvement, while tear film analysis using the Schirmer test, tear breakup time (TBUT), and ocular surface inflammation markers further support diagnosis. Corneal imaging with anterior segment optical coherence tomography (AS-OCT) or in vivo confocal microscopy (IVCM) provides detailed visualization of nerve density, epithelial integrity, and subbasal nerve plexus abnormalities.

The Mackie classification divides neurotrophic keratitis into 3 progressive stages. Stage 1 presents with early epithelial irregularities, corneal haze, reduced tear film stability, and punctate epithelial erosions. Stage 2 involves a PED with underlying stromal involvement, often leading to stromal thinning and edema (see Image. Stage 2 Neurotrophic Keratitis). Stage 3 represents the most severe form, characterized by corneal ulceration, stromal melting, and potential perforation, which significantly increases the risk of infectious keratitis and permanent vision loss. Early recognition and classification are crucial for guiding treatment and preventing disease progression.

Management of neurotrophic keratitis depends on disease severity and focuses on promoting corneal healing, restoring nerve function, and preventing complications. Treatment is multimodal, incorporating topical, surgical, and regenerative approaches. Conservative medical therapy serves as the first-line intervention, including lubrication with nonpreserved artificial tears, hydrogel inserts, and autologous serum tears to maintain ocular surface hydration. Discontinuing toxic medications, such as preserved eye drops, glaucoma drugs, and long-term corticosteroids, is essential to prevent further epithelial toxicity. Therapeutic contact lenses, including bandage, scleral, and amniotic membrane lenses, can support corneal healing in patients with PEDs.

For more advanced cases, biological and pharmacologic treatments have transformed neurotrophic keratitis management. Recombinant NGF (cenegermin-bkbj, Oxervate™) stimulates corneal nerve regeneration and enhances epithelial healing. Platelet-rich plasma (PRP) and autologous serum drops, which contain epithelial growth factors and anti-inflammatory cytokines, support ocular surface repair and reduce inflammation.

Surgical and interventional approaches are reserved for severe or refractory cases. Tarsorrhaphy, a partial or complete closure of the eyelids, reduces corneal exposure and promotes healing. Amniotic membrane transplantation (AMT) provides growth factors and anti-inflammatory properties to facilitate epithelial recovery. Corneal neurotization, a novel technique involving the transplantation of sensory nerves, such as the supraorbital or infraorbital nerve, has shown promise in restoring corneal sensation in severe cases. For patients with corneal perforation, conjunctival flaps and keratoplasty procedures, including lamellar or penetrating keratoplasty (PKP), may be necessary.

Managing neurotrophic keratitis requires an interprofessional approach involving ophthalmologists, cornea specialists, neurologists, and optometrists. Early referral to an ophthalmologist is essential, as delayed diagnosis can lead to irreversible corneal damage.

The future of neurotrophic keratitis treatment lies in regenerative medicine, neuroprotection, and gene therapy. Emerging therapies, including mesenchymal stem cell therapy, gene-based neurotrophic factor delivery, and bioengineered corneal substitutes, offer hope for improved outcomes. Advances in biologic treatments, regenerative medicine, and corneal neurotization are transforming the treatment landscape, enhancing both visual prognosis and quality of life. Increased awareness, research, and accessibility of novel therapies will be crucial in optimizing long-term patient outcomes.