Corneal Neurotization Improves Sensory Function, Epithelial Health

Adults and pediatric patients with neurotrophic keratopathy (NK) may present with mild symptoms, although the disease has the potential to progress with domino-like impact, resulting in persistent epithelial defect. Existing treatment typically strives for corneal stability rather than the triggering neurological factors; however, a long-term study has now measured sensory improvement after novel indirect corneal neurotization, demonstrating that the greater the recovery of sensation, the better the protection from epithelial breakdown, according to data published in American Journal of Ophthalmology.

This retrospective case series includes 23 consecutive patients (28 eyes) with stage II or III NK who received corneal neurotization at The Hospital for Sick Children, Toronto, Canada, from November 2012 to June 2019. Participants’ average age was 15.6±13.6 years, ranging from 2 to 62 years of age, and mean follow-up was 37.8±22.5 months.

Three months after surgery, 7 individuals stated they could feel an eyedrop falling onto their eye. Results measured with Cochet-Bonnet Aesthesiometry (CBA) improved significantly from the baseline mean of 3.5±9.1 mm, to 12-months post-op 44.4±19.7 mm, and maintained at 44.1±18.2 mm by 24 months. Patients reached maximum CBA at approximately 11 months (range 3 to 25 months), and all 5 corneal sectors exhibited improvement at 1 year (P <.001). Further, starting mean logMAR BCVA of 0.57±0.79 reached 0.39±0.66 by month 12 (P =.043).

There was strong positive correlation between eyes receiving fewer than 4 fascicles or 4 insertion sites and attaining CBA at least 50 mm, compared with eyes having 4 or more fascicles (P =.087) or insertion points (P =.014). With 60 mm considered full sensation, 60.7% achieved near to normal CBA of ≥50 mm by the last visit. The 16 eyes who displayed CBA of at least 50 mm showed more protection (66.6%) from epithelial breakdowns, compared with 8 eyes who had less than 50 mm and 34.6% probability not to have a breakdown event. The analysis emphasizes the “critical importance of maximizing neural input during neurotization.” 

Participants with an ipsilateral donor sensory nerve achieved higher mean CBA and rate of improvement in the first 3 months compared with those undergoing neurotization using a contralateral nerve, but by 6 and 12 months no large differences occurred. Similarly, eyes that experienced denervation <60 months prior exhibited a higher mean CBA at 3, 6, and 12 months compared with longer periods of injury, but showed no statistical differences by the final visit.

Currently, much of what is known about post-neurotization recovery is from pooled research data, although literature reviews may include diverse participant ages and backgrounds, NK etiologies, and surgical strategies. Investigations using acellular nerve allografts (ANA) have shown modest gains. The study notes that due to the lack of Schwann cells with ANA, there may be limited numbers of axons for best nerve regeneration. 

Limitations of this analysis comprised a relatively small sample of predominantly pediatric patients, no assessment of conjunctival sensitivity, and surgery only performed on eyes without active corneal complications. Strengths were long follow-up and demonstration of incremental progress across time. “It is important to maximize sensory recovery to protect against recurrent ulceration,” the investigators wrote, adding that supplemental medical therapy may well support the process of corneal neurotization and recovery.

Reference

Woo JH, Daeschler DS, Mireskandari K, Borschel GH, Ali A. Minimally invasive corneal neurotization provides sensory function, protects against recurrent ulceration, and improves visual acuity. Am Jour Ophthalmol. Published online May 1, 2022. doi:10.1016/j.ajo.2022.04.013