Medical Guide - Anatomy of an Eye

The eye is one of the most complex organs in the human body with many working parts used for the sense of sight. Eye movement is supported by muscles that help us to open, close, turn, and roll our eyes. Since our eyes are sensitive to environmental factors, they are protected with sclera, a tough outer layer of the eye that is typically white in color. The eye maintains moisture through tears that are used to kill bacteria and wash away dust and dirt.

Similar to that of a camera, the eye collects light before transforming the incoming light into a “picture”. Instead of using film to capture a scene, the human eye uses a layer of specialized cells, known as the retina, to develop the image. However, we do not actually see with our eyes at all, but rather with our brains. Our eyes are the beginning of the visual process. Here you will learn the various parts by reviewing the anatomy of the eye.

Cornea

The cornea is a transparent area of the eye that covers the iris (the colored parts of the eye), the pupil, and the anterior chamber and contains no blood vessels. While the cornea of carnivores, such as cats, dogs, and wolves, only consist of four layers, the human eye consists of five. The five layers of the human eye from anterior to posterior include the corneal epithelium, bowman’s layer, corneal stroma, descemet’s membrane, and the corneal endothelium. This curved, outer layer of the eye accounts for nearly two-thirds of the eye’s optical power.

  • Facts about the Cornea: Learn about the function of the cornea, how it responds to injury, and diseases and conditions that affect the cornea.
  • Structure of the Cornea: Descriptions of the five basic layers of the cornea and their function, including the epithelium, bowman’s layer, stroma, descemet’s membrane, and the endothelium.
  • Kids Health: Your Eyes: Information about the parts of the eye, how muscles move the eyes and lids, and how cones and rods within the eye process light.
  • Cornea Research Foundation: The Cornea Research Foundation of America provides informational topics on corneal conditions, transplants, and studies.
  • How the Eye Works: Explanation on how the eye processes light to enable us to see and what role the cornea plays in the process.

Lens

The lens is a transparent structure that lies suspended behind the iris and is used to refract light to the retina. The focal distance of the lens changes shape to help the eye focus on objects at various distances. This adjustment of the lens is similar to that of the lens in a camera and is known as accommodation. The lens is composed of three parts, the lens capsule, the lens epithelium, and the lens fibers. The lens capsule completely surrounds the lens and is composed of collagen. The lens epithelium can be found between the lens capsule and lens fibers and is used to regulate the functions of the lens. The lens fibers are thin and stretch from the anterior to posterior poles and form the bulk of the lens.

  • Lenses and Your Eyes: Information on how light is reflected and how farsightedness and nearsightedness is related to the lens.
  • Vision: Overview of the lens and how they work, as well as changes that occur to the eye that enable focus between objects far and near.
  • Eye’s Lens Structure: Diagram and description of the lens of the eye and how it relates with the cornea.
  • Model of the Eye: Images of a healthy eye, as well as normal vision verses an eye that is near or far sighted.
  • Guide to How the Eye Sees: In depth guide on how the eye works and a description of each of the components that make up the human eye.

Iris

The iris is the circular, thin, colored part of the eye that is responsible for controlling the amount of light the pupil is exposed to, as well as the pupil’s diameter. The pigment on the iris determines your eye color, which can be blue, green, brown, or a combination of these colors to create hazel, gold or grey. When light reaches the iris, the muscles that are attached will either contract or expand, making the pupil larger or smaller. The larger the pupil appears, the more light that can enter. The iris is composed of three layers, the endothelium, stroma, and epithelium.

  • The Iris: Learn about the three layers of the eye, endothelium, stroma, and epithelium, as well as the two chambers, anterior and posterior chambers.
  • The Eye and Its Parts: Drawings of the eye, the iris, and the many other components that make up the human eye.
  • How Does the Human Eye Work: Glossary of common eye terms and information on how a camera is similar to the lens in the eye.
  • Iris and Pupil: Description of the iris and the pupil within the human eye and their functions.
  • Parts of the Eye: Brief overview of the various parts of the eye, including the iris, sclera, cornea, pupil, and anterior and posterior chambers.

Conjunctiva

The conjunctiva is a mucous membrane composed of basement membrane and cells that line the inside walls of the eyelids, as well as the sclera (white area of the eye). Its function is primarily to lubricate the eye by producing tears and mucus which helps prevent microbes from entering the eye. The conjunctiva is separated into three main parts, the palpebral or tarsal conjunctiva which lines the eyelids, the bulbar or ocular conjunctiva which covers the eyeball above the sclera, and the fornix conjunctiva which forms the junction between the palpebral and bulbar conjunctives. The fornix conjunctiva also allows the eyeball and eyelids to move freely. 

  • Conjunctiva: Learn about the various parts of the conjunctiva as well as each of their functions.
  • Anatomy of the Eye: Diagram and descriptions of the muscles and parts of the eye, including the conjunctiva, extraocular muscles, and more.
  • Conjunctiva Eye Anatomy: Information about the conjunctiva that covers the outside surface of the eyeball.
  • Pink Eye: Conjunctivitis: Details about the most common type of infection of the conjunctiva, pink eye.
  • Blue Histology: The Eye: List of topics on the anatomy of the eye, including the parts, lab guides, and images.

Optic Nerve

The optic nerve is used to transmit information from the retina to the brain. Located in the back of eye, the optic nerve is the second of twelve cranial nerves considered to be part of the central nervous system. The fibers are covered in myelin and are encased within the meninges. The optic nerve is composed of support cells and retinal ganglion cells. Its primary function is to relay electrical impulses to allow images to form. There is a blind spot at the point of the optic nerve where no retinal photoreceptors can respond to light.

  • The Optic Nerve: Q&A: Find answers to common questions about the optic nerve, including how optic nerve damage is detected.
  • Optic Nerve Disorders: Topics of optic nerve disorders, such as Ischemic Optic Neuropathy, Optic Neuritis, and Papilledema.
  • The Optic Nerve: Diagram of the optic nerve that names each part, including nerve fibers, pores in lamina cribrosa, and the optic cup.
  • Eye Anatomy: The Optic Nerve: Information and video explaining the various components related to the optic nerve.
  • Brain: Optic Nerve: Video that describes the various parts of the topic nerve and how it carries information.

Macula

The macula is an oval-shaped yellow pigmented spot located near the center of the retina. Near the center of the macula is the fovea, a small pit that consists of cone cells that are responsible for the sharp, clear vision we use to read find print. The macula observes blue and ultraviolet light and protects the retina as light enters the eye. The light that enters the eye is converted into nerve signals within the fovea using photoreceptors.

  • Normal Macula: Photograph of a normal macula, as well as information about macular degeneration, risk factors, prevention, symptoms, and diagnosis.
  • What is the Macula: Information and diagram of the macula, as well as information on age-related macular degeneration (AMD).
  • Understanding AMD: Details on age-related Macular Disease (AMD) and how the macula of the eye processes images.
  • Macular Holes: Information on how the macular works and what can occur to our vision when the eyes develop a macular hole.
  • The Macula: Description of the macula and the fovea centralis, as well as information on color vision and deficiency.

Retina

The retina is a tissue that lines the inner surface of the eye and is light sensitive. When light reaches the retina, it initiates chemical and electrical impulses that trigger nerve signals that are sent to the brain through the optic nerve. As a complex, layered structure, the retina contains several layers of neurons and photoreceptor cells that are interconnected by synapses. There are two main types of neurons, rods that provide black and white vision and dim light, and cones that support perception of color and daytime vision.

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