Drops decrease tear evaporation

Cheryl Guttman Krader, BS, Pharm

Use of a commercially available artificial tear product containing propylene glycol as a demulcent and phospholipids in a proprietary emulsion technology reduces tear evaporation for at least 60 minutes post-instillations in patients with aqueous deficient dry eye disease associated with a MGD.

"Lubrication with artificial tears is a cornerstone of therapy for every patient with dry eye disease," said Dr. McCulley, the David Bruton Jr. Professor and chairman, Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas.

"While this newer phospholipid-containing eye drop was particularly formulated for patients with evaporative dry eye associated with MGD, based on the benefit it demonstrated in this study for reducing aqueous tear evaporation rate and [on] some previous research in which we found that the absolute aqueous tear evaporation rate is similar in patients with dry eye disease regardless of whether there is associated MGD, I consider [this lubricant eye drop] my first-line choice for artificial tears in all patients with dry eye," Dr. McCulley added.

"Its prolonged effect suggests that patients could potentially use it just four times a day and maintain benefit throughout the waking hours," Dr. McCulley explained. "This is a reasonable dosing schedule for an artificial tear product and one with which patients should be able to comply."

The study enrolled 12 patients with aqueous tear deficiency and obstructive MGD but without inflammation evident at slit-lamp examination and with no history of systemic diseases or medication use that could contribute to dry eye.

Aqueous tear evaporation was measured at baseline and then 30 and 60 minutes after instillation of a 40-µl drop of the artificial tear. Testing was repeated under two relative humidity conditions-25% to 35% and 35% to 45%.

Baseline aqueous tear evaporative rates were a mean of 0.092 ± 0.27 µl/cm2 /min at the lower relative humidity and 0.069 ± 0.022 µl/cm2 /min at the higher relative humidity. For both humidity testing conditions, the tear evaporative rate had decreased from baseline at 30 minutes after instillation of the artificial tears (mean values, 0.083 ± 0.16 and 0.062 ±0.13 µl/cm2 /min, respectively), and the rates measured at 60 minutes postinstillation were nearly identical to the 30-minute values. There was a strong trend for a statistically significant reduction in tear evaporation after 30 and 60 minutes.

"The persistence of the effect at the 60-minute test interval was particularly surprising," Dr. McCulley said. "If I had a crystal ball and could have foreseen these results, I would certainly have designed the study to repeat the testing even at 4 and 6 hours post-instillation."

The prolonged benefit of the artificial tear can be explained by its novel formulation. The lubricant eye drop contains HP-guar and borate that crosslink on the ocular surface to form a stable, polymer gel matrix retaining the demulcent ingredient, propylene glycol. In addition, its proprietary emulsion technology slowly releases essential lipids to replenish the lipid layer of the precorneal tear film, thereby reducing evaporation.

FYI

James P. McCulley, MD
E-mail: james.mcculley@utsouthwestern.edu

The study was supported with funding from Alcon Laboratories. Dr. McCulley is a consultant to that company.