Fort Lauderdale, FL-Contrast sensitivity and visual acuity improved in a small group of subjects with dry eye following instillation of one of three types of artificial tears administered in a study of tear layer disruption. The fact that only one solution produced an enhancement in visual performance suggests that practitioners need to match a patient's dry eye subtype with an appropriate artificial tear supplement to gain the most improvement, said William H. Ridder III, OD, PhD, FAAO.
Dr. Ridder, professor, Southern California College of Optometry, Fullerton, CA, discussed his conclusions in a presentation at the Association for Research in Vision and Ophthalmology. A paper on the study has been accepted for publication.
"We were interested in seeing how vision is affected by the application of various artificial tears," Dr. Ridder said. "We had already looked at normal subjects to see how vision was affected. Based on those findings, we postulated that vision might be improved in subjects with specific types of dry eye by different types of artificial tears."
"For these subjects, vision was improved when we applied a single drop of a very-low-viscosity artificial tear," Dr. Ridder said. "If we used a more viscous artificial tear, their visual performance did not improve. The main clinical outcome from this study is that we are going to need to start looking at the patient's dry eye subtype to determine what is the best artificial tear for the patient."
Measuring contrast sensitivity
The subjects, who were all adapted to contact lens wear, were fitted with a new Focus Night & Day hydrogel lens (CIBA Vision) for the experiments. A temporal, two-alternative forced-choice paradigm was used to measure contrast sensitivity. Stimuli were presented 2 seconds after blink detection (the control data obtained before tear layer breakup) or 4 seconds after the average tear film breakup time (the experimental data).
The initial measurement consisted of contrast sensitivity without any artificial tear added. A drop of an artificial tear was then applied every 10 minutes during an hour-long sensitivity assessment; the subjects did not know which tear was used. Only one tear product was used during each test session to avoid an interaction, and sessions were at least 24 hours apart. The short-term effect of a single-drop instillation was also measured by continually monitoring contrast sensitivity for a 14-cpd (cycles per degree) grating.
Grouped data indicated that without supplementation, high spatial contrast sensitivity and visual acuity were reduced following tear film breakup. The instillation of Sensitive Eyes improved contrast sensitivity and visual acuity to the level before tear breakup, while Clerz2 and GenTeal produced no enhancements in visual performance. Sensitive Eyes yielded the best results in four of the five subjects, and Clerz2 gave the best results in the remaining individual. In addition, Clerz2 and GenTeal caused a short-term decrease in contrast sensitivity.
These results suggest that the main benefit to the patients in this study was fluid supplementation to the tear layer and that this might be the only treatment necessary to improve visual performance in subjects with evaporative dry eye, although not necessarily with other types of dry eye, he said.
Clerz2 and Sensitive Eyes were chosen for the study because they are contact lens rewetting drops. Sensitive Eyes is very similar to isotonic saline solution and has very low viscosity. Clerz2 contains hydroxyethylcellulose and a polymer 406 and is slightly more viscous, while GenTeal is a very viscous supplement containing 0.3% hydroxypropyl methylcellulose. Although it is not approved for use with contact lenses, it was included to enhance the study of the effect of viscosity on prolonging visual performance, Dr. Ridder said.
This study only looked at visual performance rather than any medical benefit of artificial tears, an area in which a high-viscosity artificial tear might have an advantage by staying in the eye longer and providing more symptom relief, he added.