Glassy eyes can be understood as a fixedly staring and wide-eyed appearance. While some people say it is the watery eyes. Actually it is the sign of the dehydration. Because your body lacks water, your eyes may appear such problems. Your eyes may get dry and cause the excretion with no control. That is why you have got the glassy eyes.
Well, yes, glassy eyes can be a sign of dehydration. Generally speaking, if a person's eyes appear shiny or have a glassy appearance that means he/she is suffering from glassy eyes. And according to some experts, when someone has glassy eyes, his eyes will have a feeling of listlessness, and the eyes are unfocused, and without any luster. And when you have dehydration, it will cause the eyes to become dry, and leading to glassy eyes. Also, some people who are heavy drinkers will have glassy eyes too. So just pay more attention to your eyes.
Glassy eyes could be interpreted as a lack of focus of your eyes, once got it, you appear to be caring about nothing and looks quite like a nerd. Anyway, you should pay attention to your eye health. And on the other hand, dehydration has nothing to do with glassy eyes, because glassy eyes is primarily resulted from some mental problems or brain problems. Just try to have a medical exam first.