Eye dropsThough many eye drop prescription labels instruct patients to use one or two drops, consumers should only use one drop because there is a lesser risk of overdosing, Public Citizen writes in a new September posting on its WorstPills.org Web site.

"By improperly applying eye drops, consumers are putting themselves at risk of overdosing the medication and causing an adverse reaction," said Dr. Sidney Wolfe, director of Public Citizen's Health Research Group. "Applying only one drop can be more effective if that drop is applied correctly."

The consumer advocacy organization cited information published in the June 19 issue of The Medical Letter on Drugs and Therapeutics.

The volume of liquid contained in one eye drop varies with the thickness of the solution, the design of the dropper and the way in which the patient uses the dropper to dispense drops.

By administering a second drop, consumers could lower the effectiveness of the first drop by flushing it out or increase the risk of having an adverse reaction by allowing the medication in the drops to enter the blood stream.

A human eye can hold up to 10 microliters of liquid at a time, whereas a single droplet from an eyedropper can range from 25 to 50 microliters.

The excess medicine has only two places to go -- streaming down the patient's face in harmless, but expensive, tear-like rivulets or through a small duct in the corner of the eye and into the nose, where it is absorbed into the blood and distributed to the rest of the body.

By adhering to the following guidelines when using eye drops, consumers can ensure that they are safely getting the medication they need:

• Apply only one drop within a five-minute period -- the eye cannot hold or absorb more than a drop at a time.

• Lie down when applying drops to prevent solution "tears" from running down the face -- as much as 10 times more drug is wasted when applied in an upright position.

• Use the thumb and middle finger to apply pressure to the inside corners of the eyes for five minutes after inserting droplets to prevent the medicine from draining into the nose.

• Do not touch the dropper's tip to any surface, including the eye, to prevent contamination. Eye drops can be safely used for four weeks if they are stored tightly closed.

• Always wash your hands before applying eye drops. Use the middle finger of the hand on the same side as the eye receiving the drops to apply pressure to the inside corner of the eye to close the drainage duct. Tilt your head back, and use your index finger to pull down the lower eyelid and place a drop of medicine in the pouch. Close your eye gently and continue applying pressure for five minutes.