Purpose:
Previous studies have examined the relationship between corneal shape and normal eyelid morphology, gold weight implants, eyelid tumors or masses, prolonged gaze tasks, and eyelid surgery. Only one study, however, has examined the change in astigmatism that occurs after botox injection. That study found a reduction of with-the-rule astigmatism and an increase in against-the-rule astigmatism one month after injection; after six months there was a return toward pre-injection astigmatism. Our study will also examine whether blepharospasm and hemifacial spasm induce changes in corneal curvature that can be detected with corneal topography-to either support or contradict these previous results.
Methods:
Volunteers were selected from patients who are treated with botulinum toxin-A injections for blepharospasm and hemifacial spasm. Scheimpflug corneal topographic readings (Pentacam) were taken on the day of (and prior to) therapeutic injection. Subsequent corneal topography measurements were taken at 6 weeks after injection (the time when botox would expected to have peak effect) and 6 months after injection, or before the next injection, (the time when the botox effect would be expected to have worn off). Additionally, patients filled out 2 surveys that investigate subjective perception of symptoms; autorefraction was completed at each visit. Computer software was then used to calculate a difference map to assess for topographic shift; comparisons of shift in astigmatism to either with-the-rule or against-the-rule were also made.
Results:
There was no significant difference between eyes with hemifacial spasm and fellow eyes in regards to corneal steepness and astigmatism (p=0.74 and p=0.11). This was also true for eyes with benign essential blepharospasm compared to control for corneal steepness and astigmatism (p=0.98 and p=0.58). There were no significant changes in in astigmatism in hemifacial spasm eyes or fellow eyes at 6 weeks after botox injection and again 6 months after injection. Blepharospasm eyes did show a significant decrease in astigmatism (p=0.04) 6 weeks after injection; there was no significant change at 6 months.
Conclusions:
For the patients in our study, there were no significant differences in corneal topography between eyes with hemifacial spasm and their fellow eyes; this was also true for the comparison of eyes with blepharospasm when compared to controls. The only significant change noted in our study was a decrease in astigmatism eyes with blepharospasm 6 weeks after botox injection; there didn't appear to be a trend back toward pre-botox values 6 months after injection.
Keywords: astigmatism • cornea: clinical science