Effect of diltiazem on lid tension during light-flash-induced eye blinks in the rabbit

The purpose of this study was to examine the effect of the Ca blocker diltiazem in combination with the Ca chelator EGTA (ethyleneglycol-bis-ta-amino-ethyl ether]N,N'-tetraacetic acid) on eyelid tension generated during the light-induced eyeblink reflex in the adult rabbit. The goal is to develop nontoxic, nonsurgical therapies for blepharospasm.

Blinks were triggered in the alert rabbit, and tension was measured with a strain gauge attached to the eyelid. Strain gauge output was amplified, digitized, and stored on computer for later analysis. Experiments consisted of a set of trials in which identical light stimuli were delivered at 0.1 Hz for 5 min.

In control trials, blink tensions decreased dramatically for the first seven to nine blinks and then levelled off, indicating that with respect to muscle tension output, blinks contained both rapidly habituating and nonhabituating components. After diltiazem and EGTA were injected in the lid, blinks were reduced 30% to 90% over those in control trials. Reductions could not be explained by injection trauma or irritation due to fluid volume, because injections of saline alone did not produce such tension depression.

Diltiazem-EGTA produces a transient reduction in blink tension. A clinical application will depend on developing methods for the sustained release of these drugs in the eyelid.