When I dispense a drop of glaucoma medication into my eye from the Rx bottle, how large is that drop? Can my eye absorb or retain all of that drop, or is some of it wasted?
What is the eye's maximum capacity in terms of absorbing an eye drop?
Conventional eyedroppers deliver large and highly variable macrodoses containing 30–50 µL of ocular medications 6. (I have personally measured this at 40-60 µL, but that could be due to me squeezing the bottle harder or to the specific drops I use.)
These volumes greatly exceed the reservoir and absorptive capacities of the eye, which range between 6 and 8 µL.1 3
Excess medication volumes are associated with ocular and systemic toxicity,4,5. The excess is also costly and wasteful.
NPR Article: Drug Companies Make Eyedrops Too Big, And You Pay For The Waste October 18, 2017
Excerpt: Pharmaceutical companies have done research showing that it's possible to waste less and save consumers money. Some of that research has been around for decades.
Robin, a Baltimore ophthalmologist and adjunct professor at the University of Michigan Medical School, for example, consulted in the early 1990s with Alcon Laboratories, one of the world's largest eye care companies, when its researchers developed a so-called microdrop. Patients, he said, were able to safely and effectively deliver the tiny drops, with nothing wasted. But instead of being a breakthrough, the innovation, he said, became a case study in how business interests trump patient needs.
Bill York recalls his bosses at Alcon coming to him in the early 1990s with a pressing request. Patients were complaining that some of the company's drops caused stinging and burning in their eyes. Could he find a fix?
York, head of the research lab at the company's Fort Worth, Texas, headquarters, knew one way to ease the irritation: Make the drops smaller. The size of eyedrops isn't regulated, he said recently. Some are over 50 microliters, more than twice what the eye can hold.
So his team created a 16-microliter drop — a microdrop — that was about a half to a third of the size of most drops on the market today, he said. The team used a standard bottle with a latex dropper tip that wouldn't cause injury if it touched the eye. Then they recruited 29 glaucoma patients to test the tiny drops. Glaucoma, a leading cause of blindness in the United States, is characterized by increased pressure in the eye, which can damage the optic nerve. Daily use of medicated eyedrops preserves sight by reducing the pressure.
The patients tried different formulations of the same medication in both micro- and regular drops, which were about twice as large, for a week at a time. The researchers tracked the patients' eye pressure and side effects, such as burning, stinging, itching and dryness.
Their results were conclusive: Microdrops worked as well as larger drops to lower eye pressure. They also reduced some of the uncomfortable side effects of larger drops. And all the patients preferred using them.
York and two of his Alcon colleagues published their results in 1992 in the American Journal of Ophthalmology. Robin, who consulted on the research, was the principal investigator.
"The microdrop delivery system worked," York said recently. The drop "was manufacturable. It reduced stinging and the amount of drug needed to produce the same biologic effect. Excess drug draining out of the eye would be significantly reduced."
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