Corneal Neurotization Surgery

What Is Corneal Sensory Loss (Neurotrophic Keratopathy)? What Causes It?

Corneal sensory loss, medically known as neurotrophic keratopathy, is a serious eye condition that develops as a result of impaired sensory innervation of the cornea and is characterized by a reduced ability of the corneal surface to regenerate. This eye condition leads to a weakening of the cornea’s protective mechanisms against external factors. In particular, as these protective mechanisms weaken, reflexes do not function adequately. As a result, dryness, epithelial defects, and non-healing ulcers may develop on the eye’s surface. As the condition progresses, corneal ulcers may develop, increasing the risk of infection and potentially leading to serious complications, including vision loss. Therefore, neurotrophic keratopathy is a significant ocular surface disease that can have a progressive course and requires early diagnosis and appropriate management.

What Is Corneal Neurotization Surgery?

Corneal neurotization surgery is an advanced microsurgical treatment method performed to restore corneal innervation in patients who have developed sensory loss in the cornea. The fundamental principle of this surgery is to direct nerve fibers obtained from a healthy donor source to the cornea—either directly or via a nerve graft—thereby restoring sensory perception to the corneal surface. Since the cornea is normally densely innervated by the trigeminal nerve, the development of sensory loss results in significant functional impairment regarding epithelial regeneration, the tear reflex, and protective mechanisms; neurotization surgery aims to reactivate this biological process.

The surgery can be performed using direct (direct nerve transfer) or indirect (transfer using a graft such as the sural nerve) techniques and requires microsurgical precision. Following the procedure, nerve fibers gradually grow toward the cornea (axonal regeneration), enabling the gradual restoration of sensation. In short, corneal neurotization surgery is an innovative treatment approach that not only manages symptoms but also addresses the underlying cause of the disease, aiming to improve the long-term health and function of the corneal surface.

Who Is a Candidate for Corneal Neurotization Surgery?

There are specific patients for whom corneal neurotization is performed. To discuss these patients in detail:

• Patients with Advanced Neurotrophic Keratitis
• Patients with Trigeminal Nerve Damage
• Patients Experiencing Sensory Loss Following Herpetic Keratitis (Eye Cold Sore)

• People Who Have Undergone Acoustic Neuroma Surgery

• Patients with Corneal Damage Due to Diabetic Neuropathy
• Children with Congenital Corneal Anesthesia
• Patients Scheduled for Corneal Transplantation (Keratoplasty)
• Patients at Risk of Corneal Perforation

Corneal Neurotization Surgery Techniques

Corneal neurotization is classified into five main groups based on the surgical technique used to restore nerve loss in the cornea and the source of the nerves employed. The choice of technique depends on the patient’s overall condition, the severity of corneal damage, and the suitability of the donor nerves. The techniques described in this context are as follows:

• Direct Neurotization: This involves freeing healthy sensory nerves located just above the eye in the forehead region (supraorbital or supratrochlear nerves) and routing them directly to the edge of the cornea (limbus). In this method, no additional nerve graft is required; the nerve is guided to the eye by creating a tunnel along its natural course.
• Indirect (Nerve Graft) Neurotization: In cases where the healthy nerve source is too far away to reach the cornea directly, a nerve segment is placed to act as a “bridge.” A sural nerve graft, typically taken from the patient’s leg, is used. One end is sutured to a healthy nerve, and the other end is sutured to the cornea of the affected eye using microsurgical techniques.
• Minimally Invasive and Endoscopic Approaches: These modern techniques involve locating and transferring nerves through much smaller incisions with the aid of an endoscope, rather than traditional large incisions. This approach minimizes tissue trauma and scarring while shortening the postoperative recovery period.
• Combined Keratoplasty Technique: In patients whose cornea is both insensitive and so severely scarred as to impair vision, corneal transplantation (keratoplasty) and neurotization are performed in the same session. This technique ensures that the newly transplanted corneal tissue regains sensation quickly, thereby preventing tissue necrosis or rejection.
• Microsuture and Fascicular Distribution Technique: Under a microscope, the ends of the transplanted nerve are separated into their individual fibers (fascicles) and secured with very fine sutures to a 360-degree area around the cornea or to specific focal points. This technique aims to ensure that the nerve fibers grow evenly and healthily across the entire surface of the cornea in all directions.

How Is Corneal Neurotization Performed?

Since corneal neurotization is an advanced microsurgical procedure performed by redirecting nerve fibers from a healthy nerve source to the cornea in patients with corneal sensory loss, the patient’s corneal sensation, the underlying cause, and the suitability of the donor nerve are evaluated in detail prior to surgery. During the procedure, healthy trigeminal nerve branches in the facial region are typically preferred; if direct access is not possible, indirect neurotization is performed using a graft such as the sural nerve.

In the direct technique, the donor nerve is routed to the area near the cornea via subcutaneous tunnels, and the nerve ends are placed in the limbal region. In the indirect method, the harvested nerve graft acts as a bridge between the healthy nerve and the cornea and is secured with microsurgical sutures. Over time, the nerve fibers migrate toward the corneal tissue, forming a new sensory network.

Benefits of Corneal Neurotization Surgery

Corneal neurotization surgery offers both physical and psychological benefits to the patient. These benefits are as follows:

• The primary benefit of the procedure is the restoration of sensory nerve fibers to the cornea. As a result, the cornea becomes capable of defending itself against external factors, and natural protective reflexes (blinking, tearing) return.
• Since there is no sensation in a neurotrophic cornea, the epithelial tissue cannot regenerate, leading to non-healing ulcers. After neurotization, as corneal nutrition improves, the risk of ulcer formation is minimized.
• When nerve fibers reach the cornea, they release “neurotrophic factors” that promote the division of epithelial cells and ensure they adhere to the surface in a healthy manner. This enables the permanent closure of chronic epithelial defects.
• When the corneal surface becomes healthy and smooth, light refraction becomes more regular. Additionally, since the risk of corneal perforation is eliminated, the patient’s current visual acuity is preserved.
• If neurotrophic keratitis is left untreated, the cornea may thin and perforate. This procedure is a vital intervention that restores tissue integrity and prevents anatomical loss of the eye.
• Unlike temporary solutions such as saline drops or protective lenses, neurotization provides permanent biological healing by utilizing the body’s own repair mechanism (nerve conduction).
• Following a successful surgery, patients’ need for continuous artificial tears, antibiotic eye drops, or special bandage lenses decreases significantly, thereby improving their quality of life.
• If a corneal transplant is necessary, the prior neurotization procedure ensures that the transplanted tissue regains sensation and guarantees the healthy survival of the new tissue.

Precautions to Take Before Corneal Neurotization Surgery

There are certain key points to keep in mind to ensure a smooth surgical procedure during corneal neurotization surgery. These points are as follows:

• Detailed Ophthalmological Examination and Diagnosis: Prior to the procedure, the primary cause triggering neurotrophic keratitis (herpes infection, head trauma, tumor surgery, etc.) must be fully identified. The stage of corneal damage, tear function, and the eyelid closure reflex must be thoroughly analyzed.
• Evaluation of the Donor Nerve Site: For neurotization, nerve grafts are typically harvested from the leg (sural nerve) or the facial region (supraorbital or supratrochlear nerves). The health of the nerves in the donor site and their suitability for surgery must be assessed by a specialized team.
• Control of Active Infection and Inflammation: Performing surgery while there is an active infection or severe inflammation in the eye is risky. Any existing infections must be treated prior to surgery, and the ocular surface must be in its most stable condition for the procedure.
• Medication Management: Patients taking blood-thinning medications (such as aspirin or warfarin) must either discontinue these medications or adjust their dosage under a doctor’s supervision. Additionally, the surgeon must clarify which of the patient’s current eye drops should be continued.
• Systemic Health Assessment: Corneal neurotization is a microsurgical procedure that can sometimes take a long time. The patient’s overall health status, whether there are any conditions preventing them from receiving anesthesia, and whether chronic conditions such as diabetes—which could delay healing—are under control are of critical importance.
• Managing Expectations and Patient Education: The results of this procedure are not immediately visible. It may take months (typically 6–12 months) for nerve fibers to reach the cornea and restore sensation. Informing the patient about this healing timeline and encouraging patience helps facilitate the process.
• Maintaining Corneal Moisture: Until the day of surgery, protective measures—such as the use of artificial tears or a bandage lens—must be strictly followed to prevent the corneal surface from drying out and to ensure existing ulcers do not deepen.
• Avoiding Smoking and Alcohol: Smoking can impair microvascular circulation, negatively affecting nerve healing and graft take. It is recommended to quit smoking at least several weeks before surgery.

Precautions to Take After Corneal Neurotization

To achieve a successful outcome in corneal neurotization and optimize the healing process, the following points should be considered prior to surgery:

• Avoid Contact with Water: For the first few days after surgery (or for the duration specified by your doctor), water should not come into direct contact with the eye; you must be very careful when showering or washing your face. You should avoid environments with a high risk of infection, such as swimming pools, the ocean, and saunas, for a while.
• Monitoring Eyelid Movement: Eyelid drooping (ptosis) or eyelid closure issues may occur following corneal neurotization. If the eyelid does not close completely, this should be reported to the surgeon immediately, as the cornea may dry out and become damaged.
• Monitoring Blurred Vision and Pain: While mild discomfort and blurred vision are considered normal after surgery, you should seek immediate medical attention if you experience severe pain, sudden vision loss, or excessive redness.
• Restrictions on Strenuous Exercise and Activities: For the first few weeks, you should avoid strenuous sports that require straining, lifting heavy weights, or bending over. Such activities can increase intraocular pressure and damage the sutures or the graft site.
• Donor Site Care: If the nerve graft was taken from another area, such as the leg (sural nerve), the wound site in that area must be kept clean, and dressings should be changed regularly. Temporary numbness or tingling in the donor site is a normal part of the process.
• Patience and Long-Term Follow-Up: In corneal neurotization, nerve healing and the return of sensation can take months (typically between 6 months and 1 year). During this process, regular follow-up appointments must not be missed, and the healing progress of the corneal surface should be closely monitored by the surgeon.
• Sun Protection: Since the eye surface will be sensitive after surgery, high-protection sunglasses should be worn when going outside to prevent the harmful effects of ultraviolet rays.

The Recovery Process Following Corneal Neurotization Surgery

The recovery process following corneal neurotization surgery is gradual and long-term, due to the nature of nerve regeneration. For this reason, protecting the ocular surface is a top priority immediately after surgery, particularly during the early stages (the first few weeks). In this context, artificial tear drops, protective treatments, and regular follow-up visits are recommended for the patient.

During the first 1–3 months, as healing continues in the surgical area, the transferred nerve fibers (axons) begin to grow gradually toward the corneal tissue. Typically, the first signs of restored corneal sensation can be detected between 3–6 months; during this period, patients may notice a reduction in dry eye, accelerated epithelial healing, and improved surface integrity. Between 6–12 months, nerve regeneration becomes more pronounced, and the cornea’s protective reflexes are gradually restored. However, the healing timeline may vary depending on the patient’s age, underlying medical conditions, the extent of nerve damage, and the surgical technique employed. In conclusion, the healing process following corneal neurotization requires patience and regular follow-up; however, with proper patient selection and appropriate surgical techniques, it is a process that significantly improves corneal health and function in the long term.