Neurotrophic keratitis (NK) is a rare degenerative disease affecting the cornea, the transparent front part of the eye. The condition arises from impaired nerve function in the cornea, which diminishes sensation and disrupts the eye’s ability to repair itself. This loss of nerve signaling interferes with the blink reflex and tear production, which are needed to shield the eye and maintain its health. Without these protective mechanisms, the cornea becomes vulnerable to damage.
Underlying Causes of Nerve Damage
The health of the cornea is maintained by the trigeminal nerve, which is responsible for sensation and supports cell regeneration. Damage to this nerve is the root cause of neurotrophic keratitis. Viral infections are a frequent cause, particularly ocular herpes and shingles. These viruses can directly invade and damage the nerves supplying the cornea.
Systemic diseases can also lead to NK. Diabetes is a well-known cause, as high blood sugar levels can damage nerves throughout the body, including those in the eye. Multiple sclerosis, which attacks the protective sheath of nerves, can also disrupt corneal innervation.
Medical treatments and direct injuries are another category of causes. Damage can occur during eye surgeries or complex neurosurgical procedures. Radiation therapy targeting the head or neck can also harm the trigeminal nerve. Physical trauma, including chemical burns to the eye or head injuries that compress the nerve, can also lead to NK.
Symptoms and Disease Progression
A defining characteristic of neurotrophic keratitis is the lack of pain. Since the corneal nerves are damaged, a person may not feel irritation or injury, which can delay seeking medical care. Initial symptoms are often subtle and can include redness, tearing, light sensitivity, and blurry vision. Some individuals might also experience a foreign body sensation or notice a mucus discharge.
The disease progresses through distinct stages if left untreated. The first stage involves the breakdown of the cornea’s outermost layer, the epithelium. The surface may appear cloudy or develop dry spots and small, recurring erosions because the lack of nerve input disrupts the normal health of the epithelial cells.
As the condition worsens, it can advance to the second stage, characterized by a persistent epithelial defect (PED). This is a non-healing open sore on the cornea’s surface. The defect remains because the underlying nerve damage prevents the signals needed for wound repair. This stage presents a higher risk for complications.
The third and most severe stage involves the development of a corneal ulcer. The initial sore deepens, extending into the thicker middle layer of the cornea, known as the stroma. This can lead to corneal melting, where the tissue rapidly thins. In advanced cases, a hole, or perforation, can form, which can cause infection inside the eye, severe vision loss, or even the loss of the eye itself.
The Diagnostic Process
Diagnosing neurotrophic keratitis begins with a review of the patient’s medical history to identify known risk factors. This history provides context for why the corneal nerves might be compromised.
Next, a thorough eye examination is performed using a slit-lamp microscope. This instrument provides a magnified view of the eye, allowing the doctor to inspect the cornea for signs of NK. The physician will look for issues like epithelial cloudiness, dry spots, non-healing defects, or ulcers.
The definitive test for NK is the assessment of corneal sensation. A doctor gently touches the cornea’s surface with a sterile wisp of cotton or an esthesiometer. In a healthy eye, this touch triggers a blink reflex and a clear sensation. A reduced or absent response is the hallmark sign of neurotrophic keratitis, confirming the nerves are not functioning properly.
Management and Treatment Strategies
Treatment for neurotrophic keratitis focuses on protecting the cornea, promoting healing, and preventing progression. The approach is staggered, starting with conservative measures. This involves intensive lubrication using preservative-free artificial tears, gels, and ointments to keep the eye surface moist and shielded.
If lubrication is insufficient, interventions that provide a physical barrier for the cornea may be used. A bandage contact lens can shield the eye from eyelid friction and create a stable healing environment. Autologous serum eye drops, made from a patient’s blood, contain growth factors that support healing. Amniotic membranes can also be placed on the eye to act as a biological bandage.
A newer treatment is a medication that targets the underlying nerve issue. Cenegermin is a nerve growth factor administered as an eye drop. This therapy stimulates the regrowth and repair of damaged corneal nerves, addressing the disease’s root cause.
For severe cases that do not respond to other treatments, surgery may be necessary. A tarsorrhaphy involves partially sewing the eyelids together to narrow the opening, reducing the cornea’s exposure and protecting it. A more complex procedure, corneal neurotization, transplants a healthy nerve from another part of the body to the eye to restore sensation.