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Eye Anatomy 101

Tuesday, August 03, 2021

The human eye is one crucial aspect that we should not take for granted. The miracle of seeing the beautiful world around you is the greatest gift we have as individuals. The uniqueness of these mysterious organs is the reason that eyes make all magical experiences through sight. Did you know that the human eye can differentiate approximately 10 million different colors? The eye anatomy is very intricate and essential to understanding how our eyes can manage the value they bring to our lives. Here is a journey of the eye anatomy, starting from the front and working to the back of the eye.

Outside of the Eye

The eye sits in a protective bony socket called the orbit. There are six extraocular muscles in the orbit that is attached to the eye. These muscles move the eye up and down, side to side, and rotate the eye.

The extraocular muscles are attached to the white part of the eye called the sclera. This part of the eye is a strong layer of tissue covering nearly the entire surface of the eyeball.

The Surface of the Eye

The eye's surface and the inner surface of the eyelids are covered with a transparent membrane called the conjunctiva.

Tears lubricate the eye and make up three layers. These three layers together are called the tear film. The conjunctiva makes the mucous layer. The lacrimal gland, is where the watery part of the tears are produced. The eye's lacrimal gland sits under the outside edge of the eyebrow (away from the nose) in the orbit. The meibomian gland makes the oil that becomes another part of the tear film. Tears drain from the eye through the tear duct.

Front of The Eye

Light is focused into the eye through the clear, dome-shaped front portion of the eye called the cornea.

Behind the cornea is a fluid-filled space called the anterior chamber. The fluid is called aqueous humor. The eye is consistently producing aqueous humor. Aqueous humor also drains from the eye in an area called the drainage angle to maintain constant eye pressure.

Behind the anterior chamber are the eye's
iris
(the colored part of the eye) and the dark hole in the middle called the pupil. Muscles in the iris dilate (widen) or constrict (narrow) the pupil to control the amount of light reaching the back of the eye.

Directly behind the pupil sits the lens. The lens focuses light on the back of the eye. The lens changes shape to help the eye focus on objects up close. Tiny fibers called zonules are attached to the capsule holding the lens, suspending it from the eyewall. The lens is surrounded by the lens capsule, which is left when the lens is removed during cataract surgery. Some types of replacement intraocular lenses go inside the capsule, where the natural lens was.

By helping to focus light as it enters the eye, the cornea and the lens both play essential roles in giving us clear vision. 70% of the eye's focusing power comes from the cornea and 30% from the lens.

Back of the Eye

The vitreous cavity lies between the lens and the back of the eye. A jelly-like substance called vitreous humor fills the cavity.

The light focused into the eye by the cornea and lens passes through the vitreous to the retina; this is the light-sensitive tissue lining the back of the eye.

A tiny but specialized area of the retina called the macula is responsible for giving us our detailed, central vision. The other part of the retina, the peripheral retina, provides us with our peripheral (side) vision.

The retina sends light as electrical impulses through the optic nerve to the brain. The optic nerve is made up of millions of nerve fibers that transmit these impulses to the visual cortex — the part of the brain responsible for our sight.

References: American Academy of Ophthalmology

The content is researched and vetted by the American Academy of Ophthalmology and the American Optometric Association.

This blog provides information and discussion about eye health and related subjects. The content provided on this blog and any linked materials are not intended and should not be considered medical advice. If the reader or any other person has a medical concern, they should consult with an appropriately licensed physician



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