Blended artificial tears may cause less blurring than high-viscosity agents

September 1, 2005

Fort Lauderdale, FL—A blended artificial tear product that combines high- and medium-viscosity sodium carboxymethylcellulose (CMC) causes less blurring compared with high-viscosity tears and might be more acceptable to patients, according to the results of a small clinical study.

Refresh Liquigel and Refresh Celluvisc tears (Allergan) caused a decrease in contrast sensitivity, but contrast sensitivity returned to baseline significantly faster with the Liquigel blended preparation, investigators reported at the Association for Research in Vision and Ophthalmology annual meeting.

"One of the main complaints people have about artificial tears is that when they put them in, there is blurring of vision," said James LaMotte, PhD, OD, a professor at the Southern California School of Optometry in Fullerton. "When you put in artificial tears and things are blurred for a couple of minutes, people don't like it. This product [Liquigel] reduces blurring but still maintains a more viscous tear that has a more soothing effect on the eye."

Temporal changes in tear film structure can distort the optical wavefront as artificial tears pass through the tear layer and can reduce contrast sensitivity. In theory, any substance applied to the tear that alters its structure could affect contrast sensitivity. Dr. LaMotte and colleagues examined how different formulations of CMC applied to the tear layer affect contrast sensitivity over time.

As a stimulus, the study participants viewed monocularly a stationary, vertically oriented sine wave grating (14 cyclesper degree). A temporal, two-alternative, forced-choice paradigm combined with a self-paced method of limits was employed to monitor threshold over time.

"Patients are presented with a sine wave grating and they blink, which triggers the device and displays the grating," said Dr. LaMotte. "There are two intervals, one with grating and one without, and the patient chooses between them. The program goes back and forth, so it will go above and below the threshold."

Monitoring contrast sensitivity

Following a baseline assessment, a drop of artificial tear was applied to the tear layer, and contrast sensitivity was monitored for 30 minutes, which allowed continual tracking of the threshold.