Either atropine eye drops or ointment are placed on the eye, normally once a day. The treatment is continued as long as myopia progression is considered a risk.
Atropine has been found in several studies to reduce the progression of myopia, meaning that students who were given the drug did not become as myopic as those students without the medication. Different studies show different results. The ATOM study showed nearly a complete halt to myopic changes over a two year period: .25 units of change vs 1.20 units for the "no-drug" group. Another study (Shih 2001) found that atropine combined with multifocal glasses (to allow the student to read) had less effect: .40 units of change vs 1.40 units of change for a "no-drug" group over 18 months. Kennedy (1995) found that the atropine group had essentially no change (.05 units/year) vs. the "no-drug" group (.36 units/year). Lois Tong reported that eyes progressed in myopia faster when atropine drops are stopped. Many other studies have been done. Here's a partial listing from pubmed about atropine and myopia prevention.
Atropine was presumed for many years to have its effect due to its action of stopping the eye's ability to change focus. This was due to its action on the ciliary muscle, the muscle that controls the eye's focus. The thought was that since people who read more often (not always) became more myopic, then maybe the action of the ciliary muscle was causing the myopic changes. The story turns out to be more complicated than that. One study showed that when variables are carefully controlled, reading by itself does not cause myopia (Jones 2007) but myopic parents and lack of outdoor time do cause more myopia. (You can read more about reading and myopia in this section.) Because it is thought that atropine does not control myopia by acting on the ciliary muscle, the choroid and sclera of the eye that also respond to atropine are being investigated for their role. The short story is that we don't really know yet why atropine works as it does in the eye.
Atropine is a molecule derived from different plants that will attach itself to what are called muscarinic receptors, specific structures found throughout the body as part of the parasympathetic nervous system.
The action gets a bit complicated. For instance, atropine affects the body by blocking acetylcholine from attaching to these same receptors. Acetylcholine makes the muscle work, atropine stops it from working. If you want a general outline of the sympathetic and parasympathetic nervous system, collectively called the autonomic nervous system, here is a link to a site (Merck): Autonomic Nervous System
In the eye these muscarinic receptors can be found in two muscles (among other locations), the pupillary sphincter and the ciliary muscles and the result of atropine attaching is that the muscles can't function, becoming paralyzed until the drug wears off. Since the pupillary sphincter makes the pupil smaller and the ciliary muscle shifts the eye's focus back and forth between near and far objects, the result is an eye with a dilated pupil that can't change focus.
Atropine is a drug normally used in the eye to make the pupil bigger and to prevent the eye from being able to change focus. Doctors will say that it produces mydriasis and cycloplegia, which means the same thing. Atropine is useful to a doctor because dilation makes it possible to see more of the inside of the eye during an exam. The paralyzing of ability to change focus is useful as a treatment for some specific types of eye inflammations that cause pain due to the focusing muscle becoming inflamed. Atropine stops the muscle from working so it won't hurt so much. Atropine also helps in some other specific types of eye exams.
Atropine at high doses can be fatal but the same can be said of aspirin. Dosage levels used in the eye are considered very safe from the standpoint of extreme reactions. Unusual reactions are possible for any drug.
A person with atropine in their eye will generally be very sensitive to light because the larger pupil allows approximately 20 times as much light to enter the eye. Pupils will be large, so the student will look "different", as if they are "on-drugs", which they are. Sunglasses are necessary whenever outdoors.
The same person will also complain that they can't change focus between near and far. The focusing result will depend on their type of focusing system (nearsighted, farsighted, etc) and whether they are wearing their glasses or contact lenses for clear distance vision, but a common result is that when wearing glasses to see the board at school, a student would not be able to focus on or read the book on their desk. Normally atropine wears off in a day or two and so students after routine exams are generally told to wear sunglasses outdoors and to either take off their glasses to read or just avoid reading until things return to normal the next day or so. If the drops are used every day for myopia control, reading glasses, bifocals or removal of glasses (depending on the student's vision prescription) will be necessary for any clear vision within arms's length, such as desk work or reading.
A few students will develop red or irritated eyes.
In the United States, atropine is not approved for myopia control but could be used "off-label", meaning that the doctor can decide to use an approved drug for a non-approved reason. The patient would probably need to be given what is called "informed consent", which generally means they have been told that the drug hasn't been studied as much for safety and effectiveness for the off-label use. Low dose daily aspirin for protection against heart problems is probably the most commonly cited example of an "off-label" use of a drug but there are many others.
Due to the side effects and lack of official approval for treatment of myopia, atropine is rarely used in the United States.