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Anatomy

 

What are the extraocular muscles?

They are six muscles that are present in the eye socket and attach to the eye to move it. These muscles work to move the eye up and down and side to side and to rotate the eye.

Fig. 1 Extraocular Muscle Anatomy

What is the superior rectus?

The superior rectus is an extraocular muscle that attaches to the top of the eye. It moves the eye upward.

What is the inferior rectus?

The inferior rectus is an extraocular muscle that attaches to the bottom of the eye. It moves the eye downward.

What is the medial rectus?

The medial rectus is an extraocular muscle that attached to the inside of the eye near the nose. It moves the eye toward the nose.

What is the lateral rectus?

The lateral rectus is an extraocular muscle that attaches to the eye on the side near the temple. It moves the eye outward.

What is the superior oblique?

The superior oblique is an extraocular muscle. It comes from the back of the eye socket, travels through a small pulley in the eye socket near the nose then attaches to the top of the eye. The superior oblique rotates the eye inward around the long axis of the eye (front to back). The superior oblique also moves the eye downward.

What is the inferior oblique?

The inferior oblique is an extraocular muscle. It attaches to the eye socket in the front of the eye socket near the nose and travels outward and backward in the eye socket before attaching to the bottom part of the eyeball. It rotates the eye outward along the long axis of the eye (front to back). The inferior oblique also moves the eye upward.

What is the conjunctiva?

The conjunctiva is a transparent mucous membrane that covers the inner surface of the eyelids and the surface of the eye.

What is the lacrimal gland?

The lacrimal gland produces tears that lubricate the eye. It is located under the brow in the eye socket toward the outside.

What is Tenon’s capsule?

Tenon’s capsule is a layer of tissue that lies between the surface of the eye and the conjunctiva.

What is the sclera?

The sclera is the white outer wall of the eye. It covers nearly the entire surface of the eyeball. It is a strong layer made of collagen fibers. The tendons of the extraocular muscles attach to the sclera

What is the cornea?

The cornea occupies the front center part of the outer wall of the eye. It is made of collagen fibers in a very special arrangement so that the cornea is clear. One looks through the cornea to see the iris and pupil. The cornea bends light coming into the eye so that it is focused on the retina.

Fig. 2 The cornea occupies thee front center part of the outer wall of the eye.

Intraocular Anatomy

What is the anterior chamber?

The anterior chamber is a fluid filled space on the inside of the eye. The cornea lies in front of the anterior chamber and the iris and the pupil are behind it.

What is the iris?

The iris is the colored part of the eye that surrounds the pupil. It is disc shaped with a hole in the middle (the pupil). Muscles in the iris cause the pupil to constrict in bright light and to dilate in dim light. The change in pupil size regulates the amount of light that reaches the posterior part of the eye.

What is the lens?

The lens of the eye is located directly behind the pupil. The lens bends light coming into the eye to help focus it on the retina. The lens changes shape to help the eye focus to see objects clearly at near. The lens is suspended from the wall of the eye by many small fibers (zonules) that attach to its capsule.

What is the ciliary body?

The ciliary body is attached to the outer edge of the iris near the wall of the eye. The ciliary body produces the fluid that fills the eye and nourishes its structures. It also helps to change the shape of the lens when focusing occurs.

What is the vitreous?

The vitreous is a cavity that lies between the lens and the retina and fills the majority of the space inside the eye. It is a transparent tissue that plays an important role in nourishing the inner structures of the eye. Light that comes into the eye through the pupil and passes through the vitreous to be projected on the retina.

What is the retina?

The retina is thin, transparent structure that covers the inner wall of the eye. The eye works like a camera and the retina is similar to the film in the camera. It is where images are first projected before they are transmitted through the optic nerve to the brain. It is a very complex structure with 10 layers of specialized cells including the photoreceptor cells (rods and cones).

What are photoreceptors?

Photoreceptors are highly specialized cells of the retina that receive light impulses and change them into chemical energy that can be transmitted by nerve cells to the brain. The two types of photoreceptors are rods and cones. Rods perceive black and white and serve night vision primarily. Cones are responsible for color perception and central vision.

What is the macula?

The macula is a small specialized area of the retina that has very high sensitivity and is responsible for central vision. It is the area in the posterior retina that is bordered by two branches of blood vessels that come from the optic nerve and head toward the side of the eye that is away from the nose.

What is the retinal pigment epithelium?

The retinal pigment epithelium is a layer of cells deep to the retina. This single layer of cells helps maintain the function of the photoreceptor cells in the retina by processing vitamin A products, turning over used photoreceptor segments, absorbing light, and transporting nutrients in and out of the photoreceptor cells.

What is the choroid?

The choroid is a tissue layer that lies between the retina and the wall of the eye or the sclera. The choroid has a rich supply of blood vessels that nourish the retina.

What is the uveal tract?

The uveal tract is a pigmented component of the eye that is comprised of 1) the iris, 2) the ciliary body, and 3) the choroid.

What is the optic nerve?

The optic nerve connects each eye to the brain. It is a structure that sends the picture seen by the eye to the brain so that it can be processed. The optic nerves end in a structure called the optic chiasm. In an adult the optic nerve is about the diameter of a pencil. There are over 1 million individual nerve cells in the optic nerve.

What is the optic chiasm?

The optic chiasm is the place in the brain where the two optic nerves meet. The individual nerve fibers from each nerve are sorted in the chiasm. The sorting occurs in such a way that the right side of the brain controls the view of objects in left visual space and the left side of the brain controls the view of objects in right visual space [See figure 3].

Fig. 3 The optic chiasm is the place in the brain where the two optic nerves meet.

What is the visual cortex?

This is an area of the brain in the posterior occipital lobe to which the neurons in the retina ultimately give visual information. The visual cortex helps to process information regarding the image such as its color, composition, and relation in space to other objects. This information is then sent to other parts of the brain that serve higher visual functions.