Why do some eye drops need to be refrigerated?

Some evidence suggests that some of the glaucoma medications may be subject to degradation or breakdown if they get too warm or are kept too long at room temperature. This is generally not a major concern, however, if the medications are used as instructed and are not exposed to extremely high temperatures (like being left in a car in the hot sun). Some individuals also prefer to refrigerate their drops so that they can more easily determine if they put the drop in their eye properly, or the drop may feel more soothing and comfortable if cool when instilled.