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Mid-viscosity drops help improve tear film breakup time, study suggests
A blend of high- and medium-viscosity carboxymethylcellulose was more effective on dry eyes than similar drops of low viscosity.
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Artificial tears with a blend of medium- and high-viscosity carboxymethylcellulose increased tear film breakup time more effectively than other drops, according to a recent study.
Peter A. Simmons, PhD, and colleagues found carboxymethylcellulose (CMC) to be effective in extending the relief period for dry eye patients after administration. “It makes the tear fluid much thicker so that it no longer breaks up for substantial periods [of time],” Dr. Simmons said.
A mixture of 0.35% high-viscosity and 0.65% medium-viscosity CMC found in Refresh Liquigel (Allergan) increased the tear film breakup time (TBUT) from 3.8 seconds at baseline to 14 seconds for up to 5 minutes after the drops were used.
The study included 39 patients with dry eye symptoms and a short TBUT of about 3 seconds, as opposed to the normal 15 to 20 seconds. The mean age of the patients in the study was 62 years.
Each subject was dosed on 3 successive weeks with one standard drop of three artificial tear formulas, including Refresh Liquigel. TBUT was recorded at 5-minute intervals up to 20 minutes and then at 30, 45 and 60 minutes after each instillation.
TBUT was measured after the instillation of a minimal amount of 2% fluorescein onto the ocular surface.
“This is actually a crossover study, which is a fairly robust study design in order to show a difference, because you are actually looking at how each patient responded to all three products. Therefore, you are comparing a patient to himself basically,” Dr. Simmons explained.
The other two products analyzed in the study were a brand of drops from Allergan with 0.5% low-viscosity CMC as the active ingredient and a generic drop with hydroxypropyl methylcellulose as the active ingredient. The latter was used as a comparator.
Blink interval ratio
The study authors also measured the breakup time-blink interval ratio, according to Dr. Simmons. This is the ratio of the TBUT to the normal blink interval.
“If your blink interval is once every 10 seconds and your breakup time is 15 seconds, you will always blink before your tears would’ve broken up. So in that case, the ratio would be 1.5, and the cornea is always protected by an intact tear film,” Dr. Simmons explained.
The pre-drop blink interval ratio average was 0.49, indicating lack of protection in the subjects studied. According to the study report, the blink rate was recorded using a standardized video method at the beginning and end of each testing period.
At the peak period of effectiveness, 5 minutes after instillation of the drops, 59.7% of the patients had a blink ratio greater than 1 after being treated with the higher-viscosity CMC drops. Only 28.9% had a ratio greater than 1 after instillation of the low-viscosity CMC drops and 22% after instillation of the generic drops.
Although the percentages go down over time, Dr. Simmons noted that at the 20-minute mark a quarter of patients using the higher-viscosity CMS tears (Refresh Liquigel) still had a ratio greater than 1 while the ratio went back down to baseline after using the comparator tears.
Long-term effects
The study of TBUT, although effective in examining the immediate benefits of a high-viscosity CMC drop, does not come to any conclusions regarding the long-term effects of the drops, Dr. Simmons said.
“One needs to always take this sort of data with a grain of salt, that while it is suggestive that it is beneficial to the ocular surface, we are not actually showing the treatment effect. That’s another type of study all together,” he said.
One such study of 103 subjects using the drops four times a day for 1 month showed a 38.6% reduction in corneal and conjunctival staining at day 7 and 51.9% reduction at day 30 compared to respective scores of 26.2% and 28.9% in patients using drops of lower viscosity.
“Bottom line for a clinician is [that] they want to see that the patient is not going to come back to them in 2 weeks and say that their eyes still feel terrible,” Dr. Simmons said.
 Fluorescein tear film breakup time at 1 sec. |  Fluorescein tear film breakup time at 2 sec. |
 Fluorescein tear film breakup time at 2.5 sec. Images: Hom M |  Fluorescein tear film breakup time at 3 sec. |
For Your Information:
- Peter A. Simmons, PhD, can be reached at Eye Care Clinical Research and Development, Allergan LLC T2-4D, 2525 Dupont Drive, Irvine, CA 92612; 714-246-5514; fax: 714-246-4002; e-mail: simmons_ peter@allergan.com.
- Allergan can be reached at 2525 Dupont Drive, Irvine, CA 92612; 800-433-8871; fax: 714-246-5913; Web site: www.allergan.com.
- Jared Schultz is an OSN Staff Writer who covers all aspects of ophthalmology. He focuses geographically on Europe and the Asia-Pacific region.