Contact lens drying and visual performance: the vision cycle with contact lenses.
OBJECTIVE
The purpose of this study was to measure the effect of precontact lens tear film break-up on visual performance.


METHODS
Four asymptomatic soft contact lens wearers had contrast sensitivity measured by a temporal, two-alternative, force choice paradigm combined with a self-paced methods of limits. Stimuli were vertically orientated sine wave gratings (0.5 to 14 cycles per degree [cpd] presented for 16.67 ms. Contrast sensitivity was measured before precontact lens tear break-up by a stimuli presented 2 s after the blink. A post-tear layer break-up measurement taken with the stimuli presented after break-up had been observed by the use of a video camera attached to a Tearscope.


RESULTS
Contrast sensitivity was found to be reduced following precontact lens tear film break-up for stimuli of 4, 6, and 10 cpd; the data approached significance at 14 cpd. Further reductions in contrast sensitivity were observed for one subject when measurements were continued for 4 s following break-up.


CONCLUSIONS
Contrast sensitivity is significantly reduced for middle to high spatial frequencies when the precontact lens tear film dries and breaks up. The combination of observations of visual performance immediately following the blink (from earlier experiments) and measurements following tear film break-up in this experiment allows description of a "vision cycle" for contact lens wearers in the interval between blinks. It is suggested that break-up of the precontact lens tear film could account for the complaints of intermittent blurred vision in some contact lens wearers and may provide a stimulus to blinking in these individuals.
Thai
Lee Choon
LC
Department of Vision Sciences, Glasgow Caledonian University, United Kingdom.
Tomlinson
Alan
A
Ridder
William H
WH
D001767:Blinking / Q000502:physiology; D003263:Contact Lenses, Hydrophilic; D015350:Contrast Sensitivity; D003890:Desiccation; D006801:Humans; D011601:Psychophysics / Q000379:methods; D013666:Tears / Q000502:physiology*; D014743:Videotape Recording; D014785:Vision, Ocular / Q000502:physiology*