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Ophthalmologists who recommend that patients use over-the-counter artificial tears should instruct patients on how to use specific products because it could save or cost patients money, according to a new study.
Lead author Bruce I. Gaynes, OD, PharmD, and colleagues looked at five artificial tear products and found that a significant variation exists in drop volume not only from product to product but also based on administration angle. That difference could financially affect patients, who, for the most part, pay out-of-pocket for those products.
The study's main objectives were to look at variance in drop volume among specific artificial tear products and examine how administration angle (either 90° or 45°) can affect drop sizes from artificial tear bottles.
Dr. Gaynes and his colleagues used a technique based on a density assessment of the drops. They looked at a 100-μl drop volume of the artificial tears and, based on that volume, determined mass and density.
"From that density measurement, we were able to determine the weight of all subsequent drops and by that, we were able to determine drop volume," he said.
The researchers used five artificial tears samples: 0.30% hypromellose with 0.25% carboxymethylcellulose (GenTeal Moderate to Severe, Novartis Ophthalmics); 1% glycerin with 1% polysorbate 80 (Refresh Dry Eye Therapy, Allergan); carboxymethylcellulose (CMC) sodium 1% (Refresh Liquigel, Allergan); 0.4% polyethylene glycol (PEG) 400 with 0.3% propylene glycol (PG) (Systane, Alcon Laboratories); and a meta-stable oil-in-water emulsion (Soothe, recently acquired by Bausch & Lomb from Alimera Sciences).
Other important parts of this equation, according to Dr. Gaynes, are that these products differ in terms of viscosity, surface tension, and density based on chemical composition.
"Some include mineral oil; some involve glycerin-each may affect drop volume in different ways" he said. "The other factor is the physical composition of the bottle-how rigid it is, in terms of elasticity and deformation. The design of the orifice tip is a contributing factor in terms of drop size as well. All of these factors differ among the various products and bottle designs."
The researchers found a significantly higher drop volume with the 90° angle versus the 45° angle for all products except the combination 0.30% hypromellose with 0.25% carboxymethylcellulose preparation.
Notably, they also found that drop volume ranged from a high of 65.9 μl (1% CMC sodium) to 30.8 μl (mineral oil emulsion) while the average number of drops per bottle ranged from a low of 238.3 (0.30% hypromellose with 0.25% carboxymethylcellulose) to a high of 441.4 (mineral oil emulsion), a marked range in available dosage considering that each product carried a labeled bottle volume of 15 ml, Dr. Gaynes said.
"That is a significant range when you consider the human inferior conjunctival sac, where most of the drop is held, is probably about 7 to 10 μl. So, when you consider that you're putting a drop of 65 μl into a container of about 10 μl, you can imagine the wastage that will occur," Dr. Gaynes said.
No drop in the bucket
When they looked at the cost ramifications of their findings, Dr. Gaynes and his colleagues found that patients using artificial tear products could save from $5 to $24 a year by holding the bottles at a 45° angle.