Acellular nerve allografts in corneal neurotisation: an inappropriate choice

Correspondence to Dr Nate Jowett, Otolaryngology–Head and Neck Surgery, Massachusetts Eye and Ear, Boston, MA 02114, USA; nate_jowett@meei.harvard.edu Neurotrophic keratopathy (NK) is a devastating degenerative disease of the ocular surface, resulting in progressive corneal epithelial defects, ulceration, melting and in severe cases perforation.1 The disease results from dysfunction of trigeminal nerve afferents to the cornea; aetiologies include herpetic infection, ocular surgery, skull base tumours and surgery, brainstem cerebrovascular accidents, and congenital trigeminal nerve hypoplasia. The pathophysiology of NK encompasses loss of trophic support to the cornea, causing morphological and metabolic disturbances, and loss of sensory feedback, resulting in impaired blink and tearing reflexes.2 Though bandage contact lenses and topical medical therapies may halt disease progression and stimulate corneal healing,3 they do not address its underlying cause. Terzis et al described reinnervation of the insensate cornea by direct surgical transfer of contralateral supraorbital and supratrochlear nerve branches to the perilimbal region as a means to reverse NK progression.4 Elbaz et al described a modification of this technique employing an interposition nerve autograft between the cornea and supratrochlear nerve to reduce procedural morbidity.5 6 The largest single-centre experience on the use of nerve autografts in corneal neurotisation for NK demonstrated compelling evidence in support of this approach,7 8 with several other centres reporting encouraging results using similar autografting techniques. The inferior performance of ANAs as compared with autografts has been attributed to the limited capacity for host Schwann cells to divide and migrate long distances away from native nerve stumps.18 Accordingly, leading experts in the field of peripheral nerve surgery advise against use of existing ANAs for repair of critical nerves, large calibre nerves or non-critical small-calibre sensory nerves where gap lengths exceed 3–4 cm.20–22 Surgeons need to be aware that Avance ANAs are not intended for use in direct sensory neurotisation procedures such as corneal neurotisation, wherein otherwise healthy sensory axons supplying non-critical tissue are redirected to restore sensory input to a distant critical region.