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Eye Anatomy – Overview

The human eye is both tough and delicate, simple and complex. It is a slightly asymmetrical sphere inside a rounded area of the skull (the eye orbit), and is filled with fluid. Some of the main eye structures are easily visible and some are beneath the surface.

Find out about Early Eye Development.

The Cornea

The cornea is the transparent front surface that curves over the iris and pupil. It is a lens which refracts (bends) incoming light to focus it at the back of the eye. LASIK and its alternative procedures such as PRK and iLASIK work on the corneal curvature to correct vision defects. The cornea is part of the eyeball’s wall and connects with the sclera. Read More about the Cornea

The Iris

This circular muscle behind the cornea is the colored part. It controls the size of the pupil in its center, which determines how much light can enter the eye. The pupil itself is not a separate structure; it is just the opening in the iris. Read More about the Iris

The Sclera

Around the iris is the “white of the eye”, the sclera. It is part of the total wall of the eyeball and connects with the cornea.

The Lens

Behind the iris is a cavity called the anterior chamber, filled with fluid, and behind that is the lens. After the cornea admits light and bends it to a focus, the lens bends it further. In a 20/20 eye, the combined refraction of cornea and lens focuses the light clearly on the retina at the back of the eye. The lens curvature is controlled by a circular muscle around it called the ciliary muscle. Read More about the Lens

The Retina

Behind the lens is a second fluid-filled area called the posterior chamber. It makes up most of the eye’s entire size. The retina is the surface that borders it in a large curve extending almost to the ciliary muscle around the lens. Retinal cells are highly light-sensitive and receive the images in incoming light, converting them to electrical energy. Read More about the Retina

The Optic Nerve

Near the center of the retina is an opening where the large optic nerve leaves the eye. In a network across the entire retina are millions of tiny nerve fibers, each one connected to a single retinal cell. They pick up the electrical energy created by that cell from image information. They converge to form the optic nerve and leave the eyeball within a nerve sheath. The optic nerve runs to the brain’s vision center, where the electrical energy it carries is interpreted by the brain. Read More about the Optic Nerve

Internal Eye Fluids

The anterior chamber, between the cornea and the lens, is filled with a fluid called aqueous humor. It bathes the lens, seeping around to its posterior side through small openings. The lens and cornea have no blood vessels and receive their nutrients from this aqueous fluid.

The posterior chamber, between the lens and the retina, is filled with a fluid called vitreous humor. It is 99 percent water although it has a gel-like consistency. It is transparent to allow light through and helps to maintain the eye’s shape. Read More about Internal Eye Fluids

Each eye has a lacrimal gland for tear production and external muscles which enable it to direct vision in any direction. There are arteries supplying it with oxygen and nutrients and veins that remove waste products. There are also nerves other than the optic nerve. They enable tear production, and carry sensory data to the brain from the eye’s parts and messages from the brain to the eye muscles.

Learn more about Intraocular Pressure (IOP).

The Tear System

Find out What is 20/20 Vision?

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