What Are Visual Defects and How Common Are They ? The human eye does alot more than allowing you to see. It is very complex and has many parts and features which can have defects. However, to understand defects you must first know how the eye works. First light passes through the cornea, which is the transparent part of the sclera, or white of the eye, which is composed of tough fiberous tissue. Behind the sclera is a watery fluid called the aqueous humor. This fluid fills a cresent-shaped space which with the cornea helps bend the light toward the center of the eye. Under the aqueous humor