Common causes for glassy eyes include viral conjunctivitis, infection with the herpes virus, hypoglycemia or low blood sugar. Some medications that affect the central nervous system can cause glassiness of the eyes, as can some illegal drugs; likewise, alcohol depresses the central nervous system, according to Disabled World, and can cause a glassy-eyed effect.
Glassy eyes can also be a symptom of an underlying disease. Those with Graves' disease or people who have elevated levels of thyroid hormones may have a glassy-eyed appearance. In general, when it is said that someone's eyes look glassy, it means that they have a listless or unfocused look that may lack luster, be shiny or glazed.
Glassy eyes may be caused by failing to blink enough. This causes the eyes to become lifeless and dry, notes Disabled World.
Most cases of glassy eyes can be treated with eyedrops. Natural tears formulations may also provide relief; Disabled World recommends using this type of product up to six times a day to help with natural production of tears.
If glassy eyes become a concern, seeking out evaluation by a medical professional, recommends Disabled World. Only a medical professional can evaluate the true cause of the condition and recommend the proper treatment plan to follow.