Subconjunctival Botulinum Toxin-A Injection as a Treatment for Neuropathic Corneal Pain

To describe a new perilimbal subconjunctival botulinum toxin type A (BTX-A) injection technique and its outcomes in patients with refractory neuropathic corneal pain.

The procedure involves BTX-A injection into the nasal and temporal perilimbal subconjunctival spaces (10 units per site, 20 units total) under topical anesthesia. Pain levels, corneal sensitivity, and adverse events were assessed during follow-up.

Two patients with chronic neuropathic corneal pain refractory to both topical and systemic treatments received perilimbal subconjunctival BTX-A injections. In patient 1, the initial lower-dose injections did not result in meaningful improvement; clinical response was observed after dose escalation to 10 units per site. Patient 2 received a single injection session (10 units per site). Both patients experienced clinically significant reductions in pain levels and reductions in corneal sensitivity as measured by Cochet-Bonnet esthesiometry within 2 weeks of the injections with the effective dose. The need for artificial tear drops decreased after each set of injections. Pain relief diminished at approximately 3 months. Subconjunctival hemorrhage and intermittent diplopia were reported, but these events were self-limited within a week, with no long-term complications observed.

Perilimbal subconjunctival BTX-A injection may offer a safe, minimally invasive adjunctive treatment for patients with refractory neuropathic corneal pain. The observed analgesic effects are consistent with putative mechanisms and other clinical observations. Larger controlled studies are needed to define optimal dosing, durability, and long-term safety.