The scores for the three main outcomes measured were totaled to arrive at the OSDI score.
The two formulations differ in that Refresh Tears is a carboxymethylcellulose-based artificial tear with purite preservatives. Carboxymethylcellulose, according to Dr. Lau, is an ionic polymer with cytoprotective properties, and purite is a stabilized oxychloro complex that dissociates into water, sodium, and chloride ions upon contact with the ocular surface, minimizing the toxic effects of a preservative. Tears Naturale Free is preservative-free artificial tears containing hydroxypropyl methylcellulose; this formulation has no toxic effect on the corneal epithelial cells, he said.
Dr. Yip, consultant, Department of Ophthalmology, Alexandra Hospital and Tan Tock Seng Hospital, Singapore, conducted a randomized, prospective clinical trial with Dr. Lau and his colleagues to compare the subjective effect of the two dry eye formulations on dry eye symptoms.
To be included in the study patients had to be 18 years or older, have symptoms of dry eye, a Schirmer's test result less than 10 mm in both eyes, and be using artificial tears for symptom relief, Dr. Lau explained.
Patients were excluded if they had ocular inflammation or allergies, used punctal plugs, had a disease of the lacrimal drainage system, wore contact lenses, or used topical steroid or immunosuppressant drugs.
Thirty-three patients were randomly assigned to Refresh Tears and 35 patients to Tears Naturale Free. The groups were comparable in age, gender distribution, and the OSDI score before treatment.
"After 3 months of treatment in the group that received Refresh Tears there were significant improvements in the ocular symptom and the environmental triggers subscales as well as in total scoring. In the group that received Tears Naturale Free, there was a significant improvement in all three subscales and in the total score. However, when the two eye drops were compared after 3 months of treatment, there was no difference between the two based on the OSDI scoring system," Dr. Lau reported.
"Dry eye symptoms improved in both treatment groups after 3 months; however, there was no difference between the eye drops in terms of improvement in the OSDI score. Since the formulations have similar efficacy, a consideration might be to use Refresh Tears, which is less expensive," Dr. Lau and Dr. Yip concluded.