In some cases, when no standard treatment exists, the new treatment is compared with no treatment. Patients who get the new treatment are in the treatment group. Patients who get the standard treatment or no treatment are in the control group. In some clinical trials, patients in the treatment group get a new medicine and patients in the control group get a placebo. This treatment, like a placebo, has no effect on the eye disease or disorder and does not harm patients.
Researchers assign patients randomly to the treatment or control group.
This is like flipping a coin to decide which patients are in each group. Patients do not know ahead of time which group that is. The chance of any patient getting the new treatment is about 50 percent. Patients cannot request to receive the new treatment instead of the placebo or sham treatment. In some clinical trials, where the disease or disorder affects both eyes, one eye may be in the treatment group, and the other eye may be in the control group.