Common causes of glassy eyes include drug and alcohol use, the use of certain prescription medications, eye infection, allergies, thyroid problems and low blood sugar, according to Disabled World. MedlinePlus states that glassy eyes are a symptom of cholera, an infection of the small intestine.
Dictionary.com defines a glassy-eyed person as staring fixedly or having an expression that is dull, dazed and uncomprehending. If a medical condition is causing glassy eyes, Disabled World recommends visiting a doctor to treat the underlying problem. Certain types of eye drops can make the eyes look less glassy, and use of natural tears can help the eyes produce more tears and correct the glassy-eyed appearance.