What are the basics of eyes and vision?

Vision is dependent on the ability of eyes to focus and convert light into electrical signals, which then travel along the optic nerve to the brain to be processed into images.^[1] Light initially passes through the cornea at the front of the eye, then through an opening called the pupil, the size of which is controlled by the iris, the colored part of the eye. Light then passes through the lens, which focuses the light on the retina, a structure at the back of the eye containing photoreceptor cells that turn the light into electrical signals to be picked up by the optic nerve.^[2]

Major eye-related conditions include age-related macular degeneration (the macula is the part of the retina responsible for clear vision), glaucoma, cataract (i.e., a clouding of the lens), diabetic retinopathy (i.e., damage to the blood vessels of the retina due to diabetes), and dry eye.