Optical and visual impact of tear break-up in human eyes

PURPOSE. The purpose of this study was to examine the optical and visual im pact of tear break-up. METHODs. Optical quality of the eye was assessed during periods of nonblink ing by quantifying vessel contrast in the fundus image and by monitoring th e psychophysical contrast sensitivity and the spatial distribution of tear thickness changes by retroillumination. All measures were obtained from thr ee eyes either with or without a soft contact lens. RESULTS. A noticeable decrease in retinal vessel contrast and contrast sens itivity were observed soon after a blink. Both of these measures of optical quality of the eye showed a similar pattern of image degradation both with and without a soft contact lens. Although trial-to-trial variability was c onsiderable, sample means show that image contrast in the low spatial frequ ency range can drop to between 20% and 40% of initial values after 60 secon ds of nonblinking. Retroillumination of the tear film showed local intensit y fluctuations that progressively spread across the pupil with increasing t ime after the blink. CONCLUSIONS. Optical aberrations created by tear break-up contribute to the decline in image quality observed objectively and psychophysically. The de cline in image quality that accompanies tear break-up may be a direct cause of the blurry vision complaints commonly encountered in dry-eye patients.