Background To evaluate the efficacy of botulinum toxin A (BoNT-A) in reducing photophobia and dry eye symptoms in individuals with chronic migraine. Additionally, we aimed to evaluate tear film volume as a potential contributor to symptoms in these patients.

Methods Retrospective review of 76 patients who received BoNT-A for chronic migraine between 23 August 2017 and 13 December 2017 at the Miami Veterans Affairs Medical Center Neurotoxin Clinic. Demographic data and all comorbidities were queried via chart review. Standardised validated surveys were administered to assess symptoms prior to and after BoNT-A injection. Preinjection tear volumes were obtained using the phenol red thread (PRT) test.

Results Preinjection migraine, photophobia and dry eye symptom scores were all significantly correlated, p<0.05, and none were associated with preinjection PRT results. After BoNT-A, improvements in migraine, photophobia and dry eye symptoms were also significantly correlated, p<0.05 and similarly did not associate with preinjection PRT results. Photophobia scores significantly improved following BoNT-A, while dry eye symptoms significantly improved in those with severe symptoms at baseline (DEQ-5 score ≥12), p=0.027. In logistic regression analysis of all individuals with dry eye symptoms (DEQ-5 ≥6), individuals with more severe dry eye symptoms were more likely improve, OR 1.27, 95% CI 1.06 to 1.51, p<0.01.

Conclusions BoNT-A significantly improved photophobia in patients being treated for migraine and also improved dry eye symptoms in patients with severe symptoms at baseline, independent of baseline tear film volume. These improvements may be due to modulation of shared trigeminal neural pathways.