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W. H. Ridder, III, C. Hirata, D. Hwang; Does the Location of Artificial Tear Placement Effect Visual Performance?. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6259.
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Dry eye is frequently encountered and often treated with artificial tears (AT). The administration of an AT applied to the superior ocular surface can disrupt the tear layer resulting in an immediate decrease in contrast sensitivity (CS). Many doctors advise their patients to place artificial tears into the inferior cul-de-sac. The purpose of this investigation was to determine if there is a difference in the visual effect for artificial tears placed in the inferior cul-de-sac versus the superior ocular surface.
Ten normal, adult subjects took part in this project. Snellen acuity was better than 20/25 in the eye tested. The subjects had 1 hour of training with the CS measurement technique before data collection. CS to a 14 cpd sine wave grating was continually tracked (using a 2 AFC technique) before and after (minimum of 35 minutes) 25 µl of Refresh Liquigel (Allergan, Inc.) was instilled in the test eye. The subjects were randomized so that 5 of the subjects had the AT placed in the lower cul-de-sac first and 5 had it placed on the superior ocular surface first. The different AT administration locations were run on separate days. The magnitude of the loss in contrast sensitivity and the time until the maximum loss in CS were compared between the two techniques.
The averaged normalized log CS after AT administration was not different between the two techniques (0.33 ± 0.279 superior, 0.30 ± 0.221 inferior; p = 0.80). The time until the greatest loss in contrast sensitivity was not different either (85.6 ± 41.79 sec superior, 99.5 ± 67.25 sec inferior; p = 0.62). However, the variability in peak times was greater when the drop was placed in the inferior cul-de-sac.
The average loss in CS and the average time to the maximum loss in CS was not different between the two administration locations. However, the variability in the time to peak was greater when the drop was placed in the inferior cul-de-sac. This suggests that an AT applied to the inferior cul-de-sac may not mix quickly and completely with the tear layer. Factors such as a low blink rate, decreased lid tension, greater inferior cul-de-sac volume, and increased conjunctival folds may inhibit or slow tear mixing in some patients.
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