Whats the morning crust you get in the corner of your eye called and why do you get it?

Crusty eye. In a healthy person, the crust is usually dried mucus, which forms when the tears dry at night. This can be gently washed away at the sink or shower. For people with allergies, the mucus buildup may be greater. In someone with a cold, greater discharge may form if the person develops pinkeye.
Dried mucus. Mucus, which is produced as part of the tear film is an important part of your eye's health. It not only functions to help lubricate the ocular surface, but also protect it. Mucus traps debirs - pollen, dust, pollution, etc, and it will tend to collect in the inner corner of the eye. When you awaken you may notice a small grain of dried mucus in the corner of the eye.