Videonystagmography as a tool to assess blepharospasm before and after botulinum toxin injection

Background The aim of this paper was to study blinking parameters using a videonystagmography device, in order to objectively determine disability, and to assess the efficiency of botulinum toxin injection in patients with essential blepharospasm. Methods Blinking was studied using the features of pupillary occlusion (PO) as recorded on a videonystagmography device. In 23 patients presenting with essential blepharospasm, we studied the frequency, the percentage, the mean duration of PO, and the longest PO in a 5-minute test period. Patients were tested prior to botulinum toxin injection, and 1 month and 3 months after injection, respectively. PO levels lower than 0.3 s and higher than 0.3 s were studied separately. Results At 1 month after injection, botulinum toxin significantly influenced PO higher than 0.3 s, both in frequency (9.6/min +/- 8.2 on Day 0 and 4.7/min +/- 7.2 at Month 1; p=0.004), and in mean duration (0.95 +/- 0.84 on Day 0 and 0.58 +/- 0.34 at Month 1; p=0.03). On the other hand, we found no significant effect on PO lower than 0.3 s, both in frequency (32.4/min +/- 28.4 on Day 0 and 31.3/min +/- 29.0 at Month 1; p=0.7) and in mean duration (0.16 s +/- 0.04 on Day 0 and 0.15 +/- 0.03 at Month 1; p=0.04). Botulinum toxin also significantly influenced the mean duration of the longest PO (6.44 +/- 9.4 on Day 0 and 1.55 +/- 1.9 at Month 1; p=0.004) as well as the percentage of PO (29.95%+/- 24.6 on Day 0 and 13.44%+/- 11.1 at Month 1; p=0.003). Conclusions PO can be used as the indirect sign of blinking. Videonystagmography provides a real-time result, and could be used to objectively evaluate the effect of botulinum toxin treatment in essential blepharospasm patients.