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? Two things occur:
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 medicine 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 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, and other areas of the body, causing adverse effects.
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” 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 adverse effects.
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. To increase drug absorption, it is best to lie down while applying this medicine. 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 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 “Vaseline”-like character.
Glaucoma is a slowly progressing disorder in which the pressure inside the eye gradually increases. If left untreated, this elevated pressure may lead to nerve damage, decreased vision, and blindness. In general, the higher the pressure inside the eye, the greater the chance of damaging the optic nerve (the nerve to the eye that allows us to see) and losing vision. Most people with glaucoma have no symptoms until extensive, irreversible damage to the optic nerve has occurred, so it is important to have regular eye exams as you grow older. It is also important to take your medicine regularly if you have glaucoma.
To understand what causes glaucoma, it helps to start by discussing how the eye normally works. The eye can be divided into three parts. The vitreous chamber is the large, round area behind the lens. The posterior chamber is the smaller area located behind the iris and in front and to the sides of the lens. The anterior chamber is located in front of the iris. Both the anterior and the posterior chambers are filled with a clear liquid called the aqueous humor. Normally, aqueous humor flows from the posterior chamber through the opening in the iris to the anterior chamber. It leaves the eye through a small opening, called the canal of Schlemm, at the outermost edges of the iris. In glaucoma, less aqueous humor drains from the eye, raising the pressure inside the eye. The disorder is similar to blowing up a balloon: if there is no opening for the air to flow out, the pressure in the balloon steadily increases as the balloon fills with air.
Elevated pressure inside the eye can be treated in two ways:
increasing the amount of aqueous humor that leaves the eye through the canal of Schlemm; or
decreasing the amount of aqueous humor that is produced.
Drugs such as dipivefrin (PROPINE), pilocarpine (ADSORBOCARPINE, ISOPTO CARPINE), and physostigmine (ESERINE) increase aqueous humor outflow from the anterior chamber, whereas acetazolamide (DIAMOX), dorzolamide (TRUSOPT), and beta-blockers such as timolol (TIMOPTIC) decrease aqueous humor production. In either case, the total amount of aqueous humor is reduced and the pressure decreased. Timolol is often used for mild glaucoma, except for older adults who have congestive heart failure, abnormal heart rhythms, asthma, or emphysema. In these patients, pilocarpine or carbonic anhydase inhibitors like dorzolamide or acetazolamide can be an alternative choice. A prostaglandin-containing drug (latanoprost [XALATAN]) is now the most widely used eye-drop product for treating glaucoma. A combination of drugs may be necessary for more severe forms. Surgery is reserved for those people who continue to have optic nerve destruction and visual loss, in spite of multiple drug therapies.