Neurotrophic keratitis is a degenerative disease of the cornea caused by damage to the trigeminal nerve, the nerve responsible for corneal sensation. When that nerve stops working properly, the cornea loses its ability to feel pain and, more critically, its ability to heal and maintain itself. Left unchecked, the surface breaks down in stages, progressing from subtle dryness to open ulcers that can perforate the eye. What makes the condition particularly insidious is that patients often feel almost nothing while the damage accumulates, so diagnosis tends to come later than it should.
Why Corneal Nerves Do Far More Than Detect Pain
The cornea is the most densely innervated tissue in the entire body, packed with sensory nerve endings that dwarf the density found in skin or mucous membranes.1PubMed Central. Immunomodulatory Role of Neuropeptides in the Cornea Most people think of those nerves as a pain alarm, something that makes you flinch when dust hits your eye. That is one of their jobs, but it is far from the only one. Corneal nerves trigger reflexive blinking and tear production, the mechanical and chemical shield that keeps the surface moist and protected.2PubMed Central. Corneal Innervation and Sensation: The Eye and Beyond They also release signaling molecules called neuropeptides that regulate the immune environment of the ocular surface, keeping inflammation in check and coordinating defense against infection.3PubMed. The Intriguing Role of Neuropeptides at the Ocular Surface
Perhaps most importantly for neurotrophic keratitis, corneal nerves release trophic factors, growth signals that tell the surface cells to divide, migrate, and repair wounds. When healthy corneal epithelial cells get scratched, a cascade of nerve-driven signaling kicks off new cell growth to close the gap. One key part of that cascade involves acetylcholine, a chemical messenger produced locally by the nerves. Loss of that signal permanently depresses the rate at which epithelial cells can divide, which is the core problem in neurotrophic keratitis.4PubMed. The molecular basis of neurotrophic keratitis The cornea does not simply lose feeling. It loses the biological machinery that keeps itself alive.
What Damages the Trigeminal Nerve
Any injury, infection, or compression along the trigeminal nerve path, from the brainstem all the way to the corneal surface, can trigger neurotrophic keratitis. The causes cluster into a few broad categories.
Herpes viruses are the most common culprit. Both herpes simplex virus (the type that causes cold sores and herpes simplex keratitis) and varicella-zoster virus (the chickenpox and shingles virus) are well-documented as leading causes of the condition.5PubMed. Post-herpes neurotrophic keratopathy: Aetiopathogenesis, clinical signs and current therapies Herpes simplex can lie dormant in the trigeminal ganglion for years, reactivating periodically and inflaming the nerve each time.6PubMed Central. Herpes simplex keratitis: A brief clinical overview Repeated bouts of herpetic keratitis progressively destroy nerve fibers in the cornea, and after enough cycles of damage, sensation drops permanently.
Neurosurgical procedures are another significant source. Operations to remove acoustic neuromas (tumors on the hearing and balance nerve) or to decompress the trigeminal nerve for conditions like trigeminal neuralgia can injure the nerve directly.7American Journal of Ophthalmology Case Reports. Minimally invasive corneal neurotization for neurotrophic keratopathy: The potential effect of age, denervation chronicity and lesion location Other causes include diabetes (which damages small nerves systemically), chemical or thermal burns to the eye, long-term use of certain topical eye medications that are toxic to nerves, and some congenital conditions where the trigeminal nerve never develops normally.
A Disease That Hides Behind Its Own Mechanism
Here is the cruel irony of neurotrophic keratitis: the very nerve damage that causes the disease also eliminates the symptoms you would normally feel. A healthy cornea screams at you when something is wrong. Even a tiny scratch produces sharp pain, tearing, and light sensitivity. But when the cornea has lost its sensation, a large ulcer can develop without the patient noticing any discomfort at all.
Because of this, patients typically experience few symptoms, and diagnosis is often delayed until the disease has already progressed significantly.8PubMed Central. Expert consensus on the identification, diagnosis, and treatment of neurotrophic keratopathy A patient might come in for an unrelated eye check or notice blurred vision, only for the doctor to discover that the corneal surface is already breaking down. The best opportunity to reverse the damage is in the earliest stage, before ulceration begins, but catching it at that point requires the clinician to actively suspect it and test for it. Routine eye exams that do not specifically check corneal sensation will miss early disease.
How Neurotrophic Keratitis Is Staged
Clinicians have historically used a three-stage system, known as the Mackie classification, to grade the severity of the disease based on what the corneal surface looks like under examination.9PubMed. In vivo microscopic and optical coherence tomography classification of neurotrophic keratopathy In broad terms, stage 1 involves superficial irregularities and dryness, stage 2 features a persistent defect in the corneal surface that will not close, and stage 3 involves deep ulceration with potential stromal melting or perforation.
More recently, a newer classification system has expanded this to six stages, aiming to capture subtler distinctions. This system starts with stage 1 as altered sensation without visible damage to the cornea, progresses through punctate surface changes, persistent epithelial defects, stromal haze, ulceration, and finally perforation at stage 6.10PubMed. Neurotrophic keratopathy: An updated understanding The expanded system emphasizes checking corneal sensation early and distinguishing whether the deeper corneal layers are involved. This matters because treatment decisions, and how aggressively clinicians need to intervene, depend on whether the problem is limited to the surface or has reached the stroma beneath.
Testing for Reduced Corneal Sensation
The simplest and oldest test for corneal sensation involves touching the eye with a fine wisp of cotton or a calibrated nylon filament (a device called a Cochet-Bonnet esthesiometer). The filament is pressed against the cornea, and the length at which the patient first feels it indicates how sensitive the surface is. Shorter lengths mean more pressure is being applied, so a patient who only feels the shortest length has markedly reduced sensation. This approach remains widely used, and non-contact esthesiometers that use a puff of air have also been developed.11PubMed Central. The Prevalence of Corneal Sensitivity Loss in Patients with and without Dry Eye Disease
For a more detailed picture, clinicians can use in vivo confocal microscopy, a technique that images the living cornea at a cellular level. This allows direct visualization of the sub-basal nerve plexus, the dense network of tiny nerve fibers just beneath the corneal surface. In neurotrophic keratitis, these fibers are visibly reduced in number, shorter, and thinner than normal.12PubMed Central. Corneal nerve regeneration in neurotrophic keratopathy following autologous plasma therapy Confocal microscopy can also track whether nerves are regenerating in response to treatment, making it useful for monitoring as well as diagnosis.13PubMed. In Vivo Evaluation of Corneal Nerves and Epithelial Healing After Treatment With Recombinant Nerve Growth Factor for Neurotrophic Keratopathy Recent research has also used confocal microscopy to evaluate whether the stem cells at the edge of the cornea (limbal stem cells) are affected, since damage to these cells can compound the healing problem.14PubMed. Association Between Neurotrophic Keratitis and Limbal Stem Cell Deficiency
Conservative and Protective Treatments
Treatment is guided by clinical severity, with the overarching goal of promoting healing and preventing progression to stromal melting or perforation.15PubMed Central. Diagnosis and management of neurotrophic keratitis In early stages, the approach is conservative: preservative-free artificial tears to keep the surface lubricated, withdrawal of any topical eye drops that might be toxic to the nerves, and close monitoring. If a medication you are using contains preservatives like benzalkonium chloride, your ophthalmologist will likely switch it or discontinue it entirely, since these chemicals can further damage an already compromised corneal surface.
When a persistent epithelial defect develops and will not close with lubrication alone, protective strategies become more important. Scleral lenses, large rigid contact lenses that vault over the entire cornea and create a fluid-filled reservoir, have shown promise in clinical case reports and small series at any stage of the disease, preserving surface integrity and sometimes improving vision.16PubMed. Scleral Lens Use in Neurotrophic Keratopathy: A Review of Current Concepts and Practice The evidence for scleral lenses is still limited to case series rather than randomized trials, but clinicians increasingly consider them a useful option.
For defects that still refuse to heal, surgical approaches include tarsorrhaphy (partially stitching the eyelids together to protect the cornea) and amniotic membrane transplantation (placing a biological graft over the defect to encourage healing). In a comparative study, tarsorrhaphy achieved faster healing than amniotic membrane transplantation, with an average closure time of roughly ten days versus about eighteen days for amniotic membrane.17PubMed Central. A comparative study of tarsorrhaphy and amniotic membrane transplantation in the healing of persistent corneal epithelial defects Amniotic membrane transplantation achieved rapid surface healing in about three-quarters of cases in another series, and eyes that did not respond to the membrane were salvaged with tarsorrhaphy or, when perforation occurred, a corneal transplant.18PubMed Central. Amniotic membrane transplantation for severe neurotrophic corneal ulcers Both approaches are temporary shields that buy time for the surface to close, but neither addresses the underlying nerve damage.
Cenegermin and the Nerve Growth Factor Approach
The treatment landscape shifted meaningfully with the approval of cenegermin, a recombinant form of human nerve growth factor delivered as eye drops. Unlike lubrication or protective barriers, cenegermin works on the biology of the problem, supporting corneal reinnervation and stimulating healing of the epithelium.19PubMed Central. The use of rh-NGF in the management of neurotrophic keratopathy
In a pivotal randomized trial, roughly 70% of patients treated with cenegermin achieved corneal healing by eight weeks, compared with about 29% in the placebo group. By a stricter measure requiring complete clearance of all residual staining, about 65% of cenegermin patients succeeded versus about 17% on placebo.20Ophthalmology. Recombinant Human Nerve Growth Factor (Cenegermin) for Neurotrophic Keratopathy: Multicenter Randomized Vehicle-Controlled Pivotal Trial Confocal microscopy in treated patients showed increases in sub-basal nerve density and branching during treatment, suggesting that the drug was not just closing surface defects but encouraging nerve fibers to regrow.21PubMed. In Vivo Evaluation of Corneal Nerves and Epithelial Healing After Treatment With Recombinant Nerve Growth Factor for Neurotrophic Keratopathy The treatment involves six drops daily for eight weeks. It requires cold-chain storage, and the cost is substantial, which limits access for many patients.
Corneal Neurotization as a Surgical Frontier
For patients with severe or complete corneal anesthesia, particularly when the nerve damage is upstream in the brain or skull base and unlikely to recover on its own, corneal neurotization offers a more radical solution. The idea is borrowed from reconstructive surgery: a healthy sensory nerve from elsewhere (often the supraorbital nerve from the forehead, or the contralateral supratrochlear nerve) is surgically connected to the corneal limbus, essentially rewiring the eye with a new nerve supply.
In one case, an indirect neurotization using a sural nerve graft from the leg to bridge the gap between a functioning infraorbital nerve and the cornea produced marked improvement in sensation and complete healing of a corneal ulcer, with results stabilizing by six months.22PubMed. Indirect Corneal Neurotization Using the Infraorbital Nerve and Sural Nerve Interposition Graft The procedure remains relatively new and is performed at specialized centers, but early results have been encouraging enough that it is becoming a recognized option for patients who have exhausted other treatments. Factors like age, how long the nerve has been damaged, and where exactly the lesion is located appear to influence outcomes.23American Journal of Ophthalmology Case Reports. Minimally invasive corneal neurotization for neurotrophic keratopathy: The potential effect of age, denervation chronicity and lesion location
Neurotrophic Keratitis in Children
Although the disease is far more common in adults, neurotrophic keratitis does occur in the pediatric population. Both congenital and acquired causes exist in children.24PubMed. Neurotrophic Keratopathy in Pediatric Patients Congenital causes include rare conditions where the trigeminal nerve or its connections fail to develop, such as congenital insensitivity to pain with anhidrosis or Möbius syndrome. Acquired causes in children overlap with those in adults: herpes simplex or varicella-zoster infections, tumors compressing the trigeminal nerve, and trauma. However, diagnosis in children presents particular challenges. Young children cannot reliably report subtle visual changes, and corneal sensation testing requires cooperation that a toddler is unlikely to provide. Parents and pediatricians may attribute a red or watery eye to common childhood infections, delaying referral to a specialist.
Emerging Therapies Beyond Nerve Growth Factor
Cenegermin was a breakthrough, but its cost and logistical demands have motivated the search for additional options. One of the more intriguing candidates is topical insulin. Insulin acts as a growth factor at the corneal surface, promoting epithelial cell division and migration while inhibiting cell death. Early evidence has shown that topical insulin can enhance corneal wound healing in the setting of neurotrophic keratitis.25PubMed Central. Topical Insulin in Neurotrophic Keratopathy: A Review of Current Understanding of the Mechanism of Action and Therapeutic Approach The appeal is obvious: insulin is inexpensive, widely available, and already well-characterized in terms of safety. Clinical trials are still needed to determine optimal dosing and to compare topical insulin head-to-head with cenegermin, but it is a therapy worth watching.
Autologous serum eye drops, made from a patient’s own blood serum, represent another biological approach already in clinical use. Serum contains a cocktail of growth factors, vitamins, and proteins similar to what natural tears provide, and some clinicians use it as a bridge therapy. Platelet-rich plasma preparations fall into the same family of blood-derived treatments. These are not specific to neurotrophic keratitis and are used across a range of ocular surface diseases, but they fit the logic of trying to replace the trophic support that damaged nerves can no longer deliver.
How Neurotrophic Keratitis Differs from Dry Eye
One common point of confusion, both for patients and sometimes for clinicians, is the overlap between neurotrophic keratitis and dry eye disease. Both can produce a rough, irregular corneal surface. Both involve tear film abnormalities. Both can show punctate staining on examination. And reduced corneal sensation has been documented in some dry eye patients as well.26PubMed Central. The Prevalence of Corneal Sensitivity Loss in Patients with and without Dry Eye Disease The critical difference is the underlying mechanism. Dry eye is fundamentally a tear film disorder. Neurotrophic keratitis is a nerve disorder that produces secondary tear film problems. Treating neurotrophic keratitis with standard dry eye therapy, like artificial tears and anti-inflammatory drops alone, will control symptoms at best but will not prevent the disease from progressing, because the nerve-driven healing machinery is broken.
In practice, distinguishing the two requires checking corneal sensation. If you have persistent surface problems that are not responding to aggressive dry eye treatment, and especially if you have a history of herpes eye infections, prior facial or brain surgery, or a neurological condition affecting the trigeminal nerve, reduced corneal sensation should be tested for explicitly. This is a step that does not happen in every routine exam, and it is one reason neurotrophic keratitis is considered underdiagnosed.
The Risk of Limbal Stem Cell Involvement
The cornea renews its surface from a population of stem cells that reside at the limbus, the border between the cornea and the white of the eye. Recent research using confocal microscopy has identified an association between neurotrophic keratitis and limbal stem cell deficiency, meaning that in some patients, the stem cell reservoir itself may be depleted or dysfunctional on top of the nerve damage.27PubMed. Association Between Neurotrophic Keratitis and Limbal Stem Cell Deficiency When both the nerve supply and the stem cell source are compromised, the cornea faces a double hit: it has lost both the signals telling it to heal and the cells capable of doing the healing. This combination makes treatment considerably more difficult and may require stem cell transplantation in addition to therapies targeting the nerve deficit. It also underscores why early intervention matters: the longer the surface goes unprotected, the more likely the stem cells at the limbus are to become collateral damage.