A study examining the effect of artificial tear instillation on contrast sensitivity found that, in patients with dry eye a temporary loss with initial use disappears as the treatment is continued. Further investigations are evaluating if the finding reflects a benefit on the tear layer.
"It is possible that, after continued use, [the CMC solution] is not just providing relief for patients with dry eye by increasing lubrication of the ocular surface, but that it may be altering the tear chemistry or suppressing the detrimental effects of the dry eye condition in such a way that its instillation no longer disrupts the tear layer," explained Dr. Ridder, professor, Southern California College of Optometry, Fullerton.
"We are now conducting further studies using wavefront aberrometry to investigate if the tear layer stabilizes with ongoing use of this artificial tear."
Results showed that the contrast sensitivity effects of artificial tear instillation differed between patients with dry eye and normal subjects and depending on the product.
In the normal subjects, contrast sensitivity was not significantly affected by instillation of the older, lower-viscosity product at any visit. Following instillation of the newer, higher-viscosity drop, a significant loss of contrast sensitivity was noted at the 1-week and 2-week visits, but the change in contrast sensitivity with instillation was not significantly different across visits.
Among the subjects with dry eye, there was a significant loss in contrast sensitivity with the first instillation of the older product but no significant change after instillation at the week 1 and week 2 visits nor any significant difference in the change in contrast sensitivity across visits.
Instillation of the higher-viscosity drop was associated with a significant decrease in contrast sensitivity at baseline, and the magnitude of the effect was greater than that measured with lower-viscosity product. A statistically significant loss in contrast sensitivity also was measured after 1 week of use of the newer drop, but the magnitude of the change was lower than at baseline. At the final visit, instillation of this product had no significant effect on contrast sensitivity.
"These findings are consistent with previous studies we've conducted that show [that] instillation of many different artificial tears in normal subjects can affect contrast sensitivity and that the amount of loss increases with increasing viscosity of the drop," Dr. Ridder said. "Those investigations looked at the acute consequences of instillation and the observed effects are consistent with drop-induced temporary disruption of the tear layer leading to alteration of the modulation transfer function of the eye.
"However, there have not been longitudinal studies of changes in contrast sensitivity with longer-term artificial tear use," Dr. Ridder added. "Studies suggesting that the tear layer may be changing with continued treatment provided further rationale for the present investigation."
No significant changes in the slit-lamp findings were noted over the course of the study in the normal subjects or patients with dry eye. In the patients with dry eye, significant improvements in both the Schein questionnaire and OSDI were noted after 2 weeks of use of both drops.