The ocular wall is usually divided into three layers: the inner retina, the middle choroid and the outer sclera. An eyeball with aqueous humor, lens and vitreous body, just like a camera, has lenses and negatives, which is what we call retina. The quality of retina directly determines the quality of vision. All transparent structures are equivalent to the lens of a camera, mainly consisting of vitreous body, lens, aqueous humor and cornea. Its main function is to image objects on the retina.