Diurnal variation of visual function and the signs and symptoms of dry eye.

PURPOSE: Subjects with dry eye often complain of disturbances in visual function and worsening of symptoms in the evening. To clinically substantiate these reports of diurnal variations, the present study tested subjects with dry eye on a series of visual function and ocular physiology measures.
METHODS: Twenty-one subjects with dry eye were enrolled and underwent ophthalmic examinations, including best spectacle-corrected visual acuity, visual function decay as measured by the interblink interval visual acuity decay test without ocular anesthetic, reading rate test, slit-lamp biomicroscopy, and tear film breakup time. Keratitis, conjunctival redness, and corneal sensitivity were also assessed. Examinations occurred once during the morning and for a second time in the evening. Subjects also completed a modified version of the Ocular Surface Disease Index at both study visits.
RESULTS: Subjects with dry eye showed impaired visual function in the evening, as compared to that in the morning; they maintained their best spectacle-corrected visual acuity for a shorter time between blinks (P < 0.01) and had longer readings times (P < 0.05) in the evening as compared with that in the morning. These findings were qualified by Ocular Surface Disease Index results showing greater subjective visual impairment in the evening. Subjects also demonstrated a significant increase in keratitis and conjunctival redness from morning to evening testing. Less ocular discomfort was reported in the evening than in the morning; this effect significantly correlated with corneal sensitivity in the evening.
CONCLUSIONS: Subjects with dry eye experience significant diurnal variations of visual function and ocular surface physiology. These daily rhythms should be considered when designing clinical trials and when quantifying disease severity.