Corneal neurotization is a recent development in the treatment of neurotrophic keratopathy (NK). NK is a difficult to treat condition in which the loss of corneal nerve function leads to breakdown of the corneal surface and diminished healing. The result is an irregular, scarred surface which causes diminished vision and can lead to serious complications and permanent damage.
The cornea is the clear window at the front of the eye which helps to focus the light coming in to create clear images. Although it is a tiny structure, it has more nerves per square inch than any other part of the body, illustrating how important fragile and critical it is for vision. The sensory nerves that provide feeling for the cornea are key for tear production, regeneration from injury or daily wear and tear, and the protective blink reflex.
Loss of sensation in an eye leaves it more susceptible to chronic deterioration and mechanical injury. Furthermore, the natural nutrients which are crucial for healing and fighting off infections are reduced in corneal anesthesia, compounding the vulnerability. Deterioration of vision may result from erosions, ulcer, and scarring of the cornea.
NK may be caused by direct or indirect injuries to the sensory nerves of the cornea. Direct injuries refer to damage to the nerves in the eye itself. This may be caused by herpes, chemical or physical burns, ocular surgeries or lasers, eyedrop toxicity, contact lens abuse and radiation for nearby cancer. Congenital, acquired, and traumatic loss of trigeminal nerve function are indirect causes of NK. These may include conditions where the trigeminal nerve does not develop properly from birth, is damaged by tumors or aneurysms, or is harmed in serious head trauma.
Treatment often includes very frequent drops and ointments for eye lubrication, serum tears, topical recombinant nerve growth factor, contact lenses, surgical closure of the eyelids, and even eye removal. Neurotization is the first treatment for NK which may offer reversal or resolution as opposed to lifelong management.
Corneal neurotization involves surgically re-innervating the cornea by nerve transfer. This may be accomplished by either relocating a healthy nerve (direct neurotization) or utilizing a nerve graft attached to a healthy local nerve (indirect neurotization). Use of a healthy nerve may be limited by the function of the surrounding nerves and the distance necessary to reach the cornea without tension but has the advantage of not requiring a graft. For indirect neurotization, the nerve graft is attached to the one of the nearby healthy nerve branches in the eye region. The working end of the nerve graft is then secured to the edge of the cornea of the affected eye. Nerve grafts may be harvested from elsewhere on the patient’s body (autograft), or an acellular human nerve graft can be used (allograft). Typically, after surgery the eyelids are held partially or completely closed with sutures for a period of time to facilitate healing.
WHO IS A GOOD CANDIDATE FOR CORNEAL NEUROTIZATION?
Patients with moderate to severe NK may consider neurotization if they experience persistent dysfunction with corneal breakdown and poor vision for six months or longer. In general, it is ideal that patients have considered or tried alternatives such as medicated eye drops, lubrication and/or serum tears prior to progressing to surgery. In cases of treatment failure, or if the patient struggles with the care burden of cost, logistics and treatment of NK, surgery may offer the possibility of long term relief.
At the visit, the surgeon will evaluate the symptoms, ocular health, and corneal sensation. There is a grading scale for severity of NK called the Mackie Stages, which can help determine the benefit and safety of neurotization on an individual basis. If the patient is a candidate for surgery, the method of nerve transfer and selection of a graft will be discussed and decided with the patient.
This is an exciting development for doctors and patients dealing with NK, and we are pleased to offer this surgery through Fante Eye and Face Centre. Please reach out to our office with questions or to schedule a consultation.