Blink oscillations associated with dry eye

Purpose: To facilitate our understanding of the role of dry eye in the beginning of benign essential blepharospasm, our experiments investigated whether dry eye alters the excitability and characteristics of trigeminal reflex blinks. Methods : We recorded upper eyelid position using the magnetic search coil technique and/or pretarsal orbicularis oculi EMG (OOemg) activity. We evoked reflex blinks by stimulating the supraorbital branch of the trigeminal nerve (SO) and ascertained trigeminal reflex blink excitability by comparing the response evoked by the second (Test) of two identical SO stimuli to the response evoked by the first (Condition) stimulus. Results: In contrast to control subjects where a SO stimulus elicited only a reflex blink, a single stimulus elicited a reflex blink followed by one to seven additional blinks in people with dry eye. While constant for individual subjects, the interval between these blink oscillations ranged from 200 to 600 ms for different subjects. These oscillations were similar in nature to the bursts of OOemg activity that occur with the spasms of lid closure of benign essential blepharospasm. Because the ratios of test blink amplitude to condition blink amplitude was higher than that of age matched controls, dry eye often produced hyperexcitable reflex blinks. Nevertheless, since some subjects with blink oscillations exhibited normal trigeminal excitability, an increase in trigeminal excitability was not necessary for the generation of blink oscillations. Conclusions: These data demonstrate that an adaptive component of the response to dry eye modifies trigeminal reflex blink circuits to produce multiple blinks in response to a single stimulus. These blink oscillations may improve corneal wetting. Exacerbation of this adaptive process could play a role in the initiation of benign essential blepharospasm. This work was supported by EY07391 (CE).