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Many eye drop prescriptions are written with instructions for patients to use one or two drops. But which is the best — one drop or two?
According to the June 19 issue of the respected newsletter The Medical Letter on Drugs and Therapeutics, eye doctors (ophthalmologists) who consult for The Medical Letter generally agree that all eye drops should only be used in a dose of one drop because there is a smaller chance of an overdose with one drop. Also, using one drop instead of two makes more efficient use of the medicine.
Since the volume of a single eye drop can vary with the prescribed solution’s thickness, dropper design and the way in which the dropper is used, in some cases, just one drop could be an overdose.
A second drop could either wash out the first or increase the possibility of an adverse drug reaction because the medications in eye drops can enter the blood stream.
In addition, two drops instead of one doubles the cost of the prescription.
But if an eye doctor prescribes two drops regardless of these considerations, The Medical Letter consultants recommend that the drops be applied at least five minutes apart.
Worst Pills, Best Pills tells how to use eye drops and ointments
Public Citizen’s book Worst Pills, Best Pills also contains detailed instructions about how to use eye drops and eye ointments.
According to Worst Pills, Best Pills, the normal eye can hold about 10 microliters (10 millionths of a quart) of liquid. A single drop formed by an eye dropper, however, ranges from 25 to 50 microliters. What happens to the excess 15 to 40 microliters when you apply eye drops?
• Medicine overflows the eyelids and runs down your face, especially if you are upright when applying the drops. This is not a very efficient use of the medication, but is relatively harmless.
• Medicine drains from the eyes into a small opening located at the inside corner of the eye. This small opening is the entrance to a duct (the nasolacrimal, or tear, duct) through which tears and moisture normally leave the eye and drain into the nose (which is why your nose usually runs when you cry). In the nose, the medicine is absorbed into the blood supply and carried throughout the body, where it can affect the brain, heart, digestive system, lungs and airways, as well as other areas of the body.
What can be done to maximize drug absorption in the eye and minimize drug absorption through the nasal blood vessels?
• Do not apply more than one drop of medicine within a five-minute period, regardless of whether the second drop is the same or a different drug. The eye cannot hold more than one drop at a time, so an extra drop both flushes out the first drop and is diluted by it. It also increases the amount that is absorbed through the nasal blood vessels. Therefore, always wait at least five minutes between drops to give adequate time for the drug to be absorbed by the eye.
• Lie down when applying drops. This helps to prevent “tears” of solution from rolling down your face and through the nasolacrimal duct. As much as 10 times more drug is lost when you are in an upright position than when you are reclining.
• Using your thumb and middle finger (one in the corner of each eye), apply gentle pressure to the inside corner of the eye for five minutes after applying each drop to block the medicine from draining through the nasolacrimal duct. Compressing the duct for five minutes allows enough time for the drug to be absorbed through the eye and decreases the chance of complications.
• To avoid contaminating the eye drops, do not touch the applicator tip to any surface, including the eye. Store the bottle tightly closed. To ensure sterility, periodically discard used bottles of medicine. Drops can be considered safe for four weeks and ointments for three months after they have been opened.
• To apply drops, first wash your hands. With the middle finger of the hand on the same side as the eye (right eye, right hand, for example), apply pressure to the inside corner of your eye to block the drainage duct. After you have begun to apply pressure with your middle finger, tilt your head back. With the index finger of the same hand, pull the lower eyelid away from the eye to form a pouch. Place a drop of medicine into the pouch, remove the index finger, and close your eyes gently, without blinking. Keep your eyes closed and continue to apply pressure for five minutes. Do not close your eyes tightly, and do not blink.
• To apply ointment, first wash your hands. Lie down or tilt your head back. Squeeze about a quarter- to a half-inch of ointment inside your lower lid without actually touching the tube to your lid. Close your eye gently and roll your eyeball in all directions while the eye is closed to evenly distribute the medicine. Wait at least 10 minutes before applying other medicines to your eyes. If you need to apply both ointment and drops, it is best to put the drops in prior to the ointment, as the ointment will all but prevent absorption of the drops because of its viscosity.
What You Can Do
You should use only one drop rather than two if the directions on your prescription read: “Use one or two drops ...” If your physician tells you that two drops are needed, they should be administered five minutes apart.
