Benzalkonium chloride induces anterior chamber inflammation in previously untreated patients with ocular hypertension as measured by flare meter: a randomized clinical trial

The deleterious effects of benzalkonium chloride (BAK) on the ocular surface are well known. However, few clinical data are available to prove a toxic effect at the level of the anterior chamber. The laser flare meter is a reliable tool to detect low levels of inflammation in the anterior chamber. We wanted to know whether instillation of BAK-preserved timolol in one eye would result in higher laser flare values than the instillation of preservative-free timolol in the fellow eye.Randomized prospective, single-masked clinical trial. Twenty-eight untreated patients with ocular hypertension were recruited. After obtaining baseline flare values, we randomly assigned one eye to BAK-preserved timolol and the fellow eye to preservative-free timolol. After 1 month, flare measurements were repeated.There was a significant increase in the flare values in the two treatment regimens, but the increase in the BAK-treated eyes was higher than in the preservative-free treated eyes, and this difference in increase was statistically significant.This is the first study to show that short-term BAK administration produces inflammation in the anterior segment of previously untreated patients whose blood-aqueous barrier was not affected by recent intraocular surgery.