The Anatomy of the Eye
The eye is a complex, delicate and surprisingly durable structure. It is filled with fluid and can be considered in six constituent parts:
The Cornea
The transparent front surface curves over the iris and pupil. It is the lens which bends (refracts) incoming light to focus it at the back of the eye. During Intralase SBK, PRK other forms of Laser Vision Correction the corneal curvature is affected in order to correct vision defects. The cornea is part of the wall of the eye and connects with the sclera.
The Iris
This circular muscle behind the cornea is the colored part of the eye. The iris controls the size of the pupil, which in turn determines how much light enters the eye. The pupil itself is not a separate structure; rather, it is the opening in the iris.
The Sclera
Around the iris is the sclera, or “white of the eye”. It connects to the cornea.
The Lens
Behind the iris is the anterior chamber (a cavity filled with fluid), and behind this lies the lens, the curvature of which is controlled by a circular muscle around it called the ciliary muscle. After the cornea admits light and bends it to a focus, the lens bends it further, helping a person focus on things either nearby or far away. 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 Retina
Behind the lens is a second fluid-filled area called the posterior chamber, which constitutes most of the eye’s total size. The retina is the surface that borders it in a large curve extending almost to the ciliary muscle around the lens. The retina acts in a manner similar to film in a camera. It receives light from an image we are looking at, and converts that light into electrical impulses which are sent through the fibers of the optic nerve to the brain.
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.
Internal Fluids
The anterior chamber, between the cornea and the lens, is filled with a fluid called aqueous humor, which 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% water although it has a gel-like consistency. It is transparent to allow light through and helps to maintain the eye’s shape