Healthy vision is accomplished through healthy eyes—and good nutrition is vital to healthy eyes. The eye is made of various structures working in concert to focus light rays from objects into images and send them to our brain via electrical impulses. The eye itself is protected in a bony orbit (socket). The socket provides protection against trauma, but cannot protect the eye from internal injuries.
The front of each eye is covered by an eyelid, which blinks periodically to spread tears over the eye surface and remove unwanted material. The eyelids also have glands that secrete oil onto the cornea, forming a portion of the tear film of the eye.
The cornea is the transparent covering through which light travels. On all sides of the cornea (covering and shaping the rest of the eyeball) lies the sclera, which is made of tough connective tissue. This sclera is the “white” of the eye, while the cornea covers the pupil and the iris (the dark hole and colored portions, respectively). The conjunctiva (a delicate, thin layer of tissue) covers the entire surface of the eyeball and lines the inner surfaces of the lids.
Beyond the cornea lies the iris, which gives the eye its color. The iris is a sphincter made of smooth muscle that contracts and expands in response to light levels. The open area in the middle of the iris is the pupil. When the iris contracts, the pupil gets smaller, thus allowing less light to enter the eye. Conversely, when the iris sphincter muscle relaxes, the pupil dilates, allowing more light into the eye.
The area between the cornea and the iris is the anterior chamber; it is filled with a fluid called aqueous humor. The aqueous humor bathes several structures in the eye. Directly behind the iris is the lens, which is held in place by small, string-like structures called zonules. The lens and the cornea together focus all images coming into the eye.
Behind the lens, the eye is filled with vitreous humor, a clear substance with the consistency of firm jelly. Vitreous humor fills the bulk of the eyeball and gives it the round shape needed for proper image production. The inner back surface of the eye is lined with light-sensitive nerve tissue called the retina. An easy analogy is to compare the retina of the eye to the film of a camera: both capture images. The retina consists of photoreceptors (light-detecting cells), nerve fibers, and blood vessels. There are two kinds of photoreceptors: rods and cones. Rods are extremely light sensitive but detect only black and white. Cones detect colors but require more light than rods. This explains why objects in dim light often appear in shades of grey, black, or white. Together, rods and cones capture the image and send it to the brain via the optic nerve.
The most important part of the retina is the macula. This area has a very high concentration of photoreceptors and is responsible for one’s central vision. The nerve fibers in the macula and other parts of the retina coalesce to form the optic nerve, which is a sort of cable that connects the eye to the brain.
Eye health is highly dependent on healthy neurological and cardiovascular systems. Images obtained by the eye are transferred via electrical impulses to the brain, where they are processed and in turn transformed into the mental images we “see.” Thus, maintaining optimum neurological health and capacity contributes to visual functioning. Similarly, the cardiovascular system supplies the eye with oxygen-rich blood and removes waste products produced in the eye’s structures. The retina and surrounding structures are especially rich in blood vessels and rely on a healthy cardiovascular system. Many nutrients have the potential to maintain or improve the eye and its function by acting on the cardiovascular and brain systems.