The National Eye Institute is a great resource to understand eye conditions. For example, you can learn more about glaucoma–
Glaucoma is a group of diseases that damage the eye’s optic nerve and can result in vision loss and blindness. However, with early detection and treatment, you can often protect your eyes against serious vision loss. The optic nerve is a bundle of more than 1 million nerve fibers. It connects the retina to the brain. (See diagram above.) The retina is the light-sensitive tissue at the back of the eye. A healthy optic nerve is necessary for good vision. Learn more here.