Structures of the Eye

Lens

A biconvex structure that is hard and opaque in preserved specimens. The shape of the lens determines where light will be focused on the retina.

Ciliary body

A black pigmented body that appears as a halo encircling the lens. It consists of mostly muscle for controlling the tension of the suspensory ligaments. The ciliary body also secretes the aqueous humor that circulates in the anterior cavity of the eye.

Suspensory ligaments

A halo of delicate fibers attaching the lens to the ciliary body. A change in the tension of the suspensory ligaments will alter the shape of the lens and affect the focusing of light on the retina.

Conjunctiva

A mucous membrane that overlies the anterior surface of the eye and serves to protect the cornea from mechanical damage.

Vitreous humor

A thick, gelatinous substance located in the posterior cavity of the eye behind the lens. This humor helps to maintain the position of the retina against the choroid layer of the eye.

Iris

Anterior continuation of the ciliary body penetrated by the pupil. This portion of the eye gives the eye its color.

Optic nerve

Cranial nerve II can be seen exiting the back of the eye en route to the brain. This nerve carries information regarding visual stimuli to the occipital lobe.

Retina

Delicate yellowish-white membrane that easily separates from the choroid layer during dissection. The retina contains the photoreceptors necessary for vision. Neurons from sensory cells in the retina exit the eye to form the optic nerve at the optic disc.

Tapetum lucidum

Iridescent layer found in nocturnal animals for maximizing vision under low intensity light

Choroid

Posterior continuation of the ciliary body. It appears brownish-black in humans, but is iridescent in nocturnal animals (tapetum lucidum).

Cornea

The anterior most portion of the sclera. It appears cloudy in preserved specimens. The cornea is the first portion of the eye to receive light.

Anterior Cavity

The fluid-filled space inside the eye between the iris and the cornea's innermost surface, the endothelium. Aqueous humor is the clear fluid that fills the anterior chamber.

Aqueous humor

The watery liquid secreted by the ciliary body that circulates in the anterior cavity of the eye. The aqueous humor must be drained to avoid an increase in intraocular pressure (glaucoma results from a blockage in the aqueous humor drainage system).

Sclera

The white of the eye. A coat of dense connective tissue that adds to the shape of the eye and provides protection of the internal eye structures.

Pupil

a hole located in the center of the iris of the eye that allows light to strike the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil.

Suspensory ligaments of the eye

a series of fibers that connect the ciliary body of the eye with the lens, holding it in place.

Fovea Centralis

a small depression in the retina of the eye where visual acuity is highest. The center of the field of vision is focused in this region, where retinal cones are particularly concentrated.

Macula Lutea

an oval yellowish area surrounding the fovea near the center of the retina in the eye, which is the region of keenest vision.

Posterior chamber of the eye

filled with a watery fluid known as the aqueous humor, or aqueous. Produced by a structure alongside the lens called the ciliary body, the aqueous passes into the posterior chamber and then flows forward through the pupil into the anterior chamber of the eye.

Ciliary Body

includes the ciliary muscle, which controls the shape of the lens, and the ciliary epithelium, which produces the aqueous humor. The vitreous humor is produced in the the non-pigmented portion of the ciliary body.

Vitreous Chamber

largest of the three chambers and is located behind the lens and in front of the optic nerve. This chamber is filled with a thick, clear gel-like substance called the vitreous humor (also vitreous body). The humor plays a crucial role in supporting the posterior side of the lens.

Optic Disc

the raised disk on the retina at the point of entry of the optic nerve, lacking visual receptors and so creating a blind spot.

Vascular Tunic

the thick middle coat of the eye, interposed between the retina and the sclera. It is commonly referred to as the uvea or uveal tract. The vascular tunic includes three contiguous parts, which, from posterior to anterior, are the choroid, the ciliary body, and the iris.