Sense Organs: Eyes

Front 1

The eye
(ocul/o, ophthalm/o, optic/o, opt/o)

Back 1

A pair of special sense organs that converts the energy of light into electrical nerve impulses and transmits those signals to the brain where they're interpreted as sight.

Front 2

External Structures of the Eye
Eyelids

Back 2

The eyes are contained in two bony orbits at the front of the skull. About five-sixths of each eyeball lies within, and is protected by, these bony sockets. The other external structures of the eye are the eyelids (blephar/o, palpebr/o), eyebrows, and eyelashes.

Front 3

ophthalmologist

Back 3

a specialist (-ist) in the study (log/o) and treatment of disorders of the eye (ophthalm/o).

Front 4

conjunctiva

Back 4

conjunctiva—a mucous membrane (conjunctiv/o) lining the inner surface of the eyelids and the anterior part of the eye.

Front 5

lacrimal glands

Back 5

produce the tears (lacrim/o, dacry/o) that moisten the eye and the eye muscles.

Front 6

sclera

Back 6

is the tough (scler/o means hard) outer membrane that helps to maintain the size and shape of the eyeball and attaches to the muscles that move the eye. The sclera is what we recognize as the white of the eye.

Front 7

cornea
kerat/o

Back 7

(corne/o, kerat/o)—a convex, transparent structure through which light passes to other parts of the eye.
Kerat/o also means hard, horny in the context of the integumentary system and the skin. In the context of this module, kerat/o means cornea.

Front 8

choroid layer

Back 8

The choroid layer, is a thin membrane with a rich supply of blood vessels.

Front 9

iris

Back 9

Anteriorly, the choroid is joined to the iris (irid/o, ir/o), the contractile disc that forms the colored portion of the eye, by the ciliary body (cycl/o).

Front 10

pupil

Back 10

The pupil (cor/o, pupill/o) is the circular opening in the middle of the iris. Muscles of the iris constrict and dilate the pupil in response to the intensity of light.

Front 11

Lens

Back 11

The lens (phac/o, phak/o), a highly elastic, transparent structure behind the iris, is surrounded and supported by fibers arising from the ciliary body. Contraction or relaxation of the ciliary body changes the shape and size of the lens.

Front 12

fundus
(Retina, optic disk, Macla Lutea)

Back 12

the inner posterior surface of the eye. It includes the retina (retin/o) and its structures—the optic disc (papill/o) and the macula lutea. The fundus can be visualized during a procedure called ophthalmoscopy. In this procedure, an ophthalmoscope—a device consisting of a light, a mirror, and lenses of varying strengths—is used in examining (-scopy) the eye (ophthalm/o).

Front 13

Retina

Back 13

The retina is the innermost covering of the eye. It is a thin, delicate membrane that is continuous with the optic nerve, through which light impulses are transmitted to the brain. The retina itself is a multilayered structure, the outermost layer of which contains light-sensitive cells called rods and cones. A cone is a photoreceptor cell in the retina that transforms light energy into a nerve impulse. Cones are responsible for color and central vision. A rod is a photoreceptor cell of the retina essential for vision in dim light and for peripheral vision.

Front 14

Optic Disk

Back 14

Landmarks of the retina include the optic disk (also spelled optic disc), from which the optic nerve arises, and the macula lutea, an oval spot at the center of the retina. Cone cells are concentrated in the fovea centralis, a small depression in the middle of the macula that is the area of clearest vision. The optic disk, also called the blind spot, is the only area of the retina that is not sensitive to light.

Front 15

Anterior cavity
(aqueous humor)

Back 15

The anterior cavity consists of anterior and posterior chambers. The chambers of the anterior cavity (anterior chambers) contain a clear, watery fluid, called aqueous humor (aque/o = water), that helps to maintain the shape of the eyeball and to nourish the iris, lens, and cornea. A humor is any body fluid, including blood and lymph.

Front 16

Posterior cavity

Back 16

The posterior cavity of the eyeball occupies all of the internal space behind the lens. It contains vitreous humor, a gelatin-like substance (vitre/o means glassy) that also helps to preserve the eyeball's shape.

Front 17

Refraction

Back 17

Refraction refers to the bending of light rays as they pass through the cornea, lens, and other structures of the eye en route to the retina.
The refracting media of the eye are the cornea, aqueous humor, lens, and vitreous humor. These media bend the light rays so that they focus on and stimulate the rods and cones.

Front 18

Accommodation

Back 18

the ciliary body changes the size and shape of the lens by contracting and relaxing. This refractory adjustment to focus as an object draws near is accommodation. Muscles of the ciliary body produce flattening of the lens for distance vision and thickening and rounding of the lens for close vision.

Front 19

The Iris and Pupil

Back 19

When the muscles of the iris contract, the pupil constricts, eliminating light rays that cannot be sufficiently refracted to focus on the retina.

Front 20

Rods, Cones

Back 20

chemical changes produce nerve impulses, which are transmitted to the brain and interpreted as a visual image. Rods are cylindrical cells that enable the detection of low-intensity light. Most of the 120 million rods in the eye are located around the periphery of the retina. Cone cells, of which there are about 6.5 million, produce vision in bright light and help us to see color. There are three types of cone cells in the retina, each sensitive to one of the three primary colors: red, blue, and green.

Front 21

Convergence

Back 21

is the movement of the eyes in unison toward a common point of fixation. It is because of convergence that we have binocular vision, the ability to see one image using both eyes.

Front 22

binocular vision

Back 22

Fibers from the right visual fields form the right optic tract and transmit impulses to the right occipital cortex. When these images from both eyes fuse in the brain, they produce a single 3-D image, the result being called binocular vision.