Minimally Invasive, Maximally Successful

Corneal anesthesia is a debilitating condition in which the function of the ophthalmic division of the trigeminal nerve is impaired and the brain receives little or no pain sensation from the cornea. This loss of sensation, which may be congenital or secondary to a variety of causes, means that, over time, minor corneal injuries add up to significant ulceration, scarring, and ultimately blindness. Not only that, but corneal sensation is critical for limbal stem cell function, so its absence impairs repair of the corneal epithelium. Most treatment options – artificial tears, corneal or scleral contact lenses, and in more severe cases, tarsorrhaphy and keratoplasty – can help, but all fail to address the underlying problem.

All is not completely lost, though. There is a type of surgery that can address the root cause (1): corneal neurotization with locally available donor nerves (typically the supraorbital and supratrochlear nerves). But this has historically been a rather invasive approach – initial procedures took 10 hours to perform and required an incision from ear to ear across the forehead, extensive dissection, and the denervation of the contralateral forehead and scalp. But now, a team of Toronto-based surgeons have refined the procedure into a minimally invasive approach that uses a sural nerve graft from the leg (2,3). The new operation requires only a small upper lid incision to access the supratrochlear nerve for neurotization and the creation of a subcutaneous tunnel along the nasal bridge to connect the supratrochlear nerve to the globe. But crucially, it spares the supraorbital nerve – and with it, forehead sensation – and results in minimal scarring.

What happens to the patients after surgery? The team believe that the graft slowly innervates the cornea at around one millimeter per day, with sensation typically returning within six months. Those with damaged corneal epithelia might experience pain postoperatively, but once protective sensation is established, the discomfort subsides as the ocular surface is allowed to heal. Of note, patients initially reported that mechanical stimulation of the cornea felt like the cutaneous skin territory of the supratrochlear nerve was being stimulated. But over the few months following surgery, patients shifted to perceiving this as true corneal sensation – suggesting that some degree of central nervous system remodeling takes place (3). The first patient to receive the treatment experienced significant improvements in corneal clarity, and is now eligible for a corneal transplant. Of the four children and one adult who have undergone this procedure, all have experienced the development of a protective corneal sensation by six months postsurgery, and to date, follow-up has uncovered no ocular healing problems or loss of forehead sensation.