Basic Anatomy - The Eye

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Parts of the Eye

Aqueous Humor: The aqueous humor is the clear, watery fluid located inside the eye that provides the eye with nutrients.

Cornea: The cornea is the clear, dome-shaped tissue that covers the front of the eye.

Iris: The iris is the colored part of the eye. It controls the amount of light that can enter into the eye. It does this by changing the pupil’s size.

Pupil: The pupil is the opening in the center of the iris that appears to be black. It changes in size as the amount of light changes. In other words, the more light, the smaller the pupil hole and the lower the light source, the larger the pupil hole gets.

Lens: The lens of the eye is a crystalline structure located just behind the iris. Its purpose is to focus light onto the retina.

Retina: The retina is a light-sensitive tissue that lines the back of the eye. Within the retina are millions of photoreceptors known as rods and cones. The rods and cones convert light rays into electrical impulses that are then transmitted to the brain by the optic nerve.

Optic Nerve: The optic nerve is also referred to as the cranial nerve II. The nerve transmits electrical impulses from the retina to the brain which then interprets what the eye is seeing.

Vitreous: The vitreous (also known as the vitreous humor) is a thick, transparent liquid that fills the center of the eye. The liquid is made up of mostly water and it gives the eye its form and shape.

Cones: Cones are cells that are located in the retina. They sense color. Humans have three types of cones, (1) L cones which sense long wavelengths (i.e., reds, yellows), (2) M cones that sense medium wavelengths (i.e., greens), and (3) S cones that sense medium wavelengths (i.e., violets, blues).

Rods: Rods are cells that are also found within the retina. They sense the degree of brightness. When you see at night or in a dark room, it is the rods working and not the cones. The eye has far more rods than cones.

Eyebrow: The eyebrow is the patch of dense hair located above the eye. It is meant to keep dust and other foreign objects from getting into the eye.

Eyelash: Eyelashes are the tiny hairs on the edge of the eyelids and, like the eyebrow, their purpose is to protect the eye from foreign objects.

Eyelid: The eyelid is the flap of skin that can cover and protect the eye for long periods of time and remain closed during sleep.

Tear: The tear is a clear, salty liquid. It is produced by glands in the eyes. The tear is meant to clean the eye, keep it moist and if foreign objects get in, to wash the foreign object away.

Diseases of the Eye

The eye can suffer from many diseases that will affect the quality of vision. Among some of those diseases are:

Astigmatism: Astigmatism is a condition in which the lens of the eye is warped. The warped lens will cause images to appear out of focus on the retina.

Nearsightedness: Nearsightedness is also known as myopia. This is a condition in which objects that are nearby are seen clearly while objects in the distance are out of focus. This is because the light is focused in front of the retina rather than on the retina.

Farsightedness: Farsightedness is also known as hyperopia. This is a condition in which distant objects are seen more clearly than are object that are nearby. This is because light is focused behind the retina rather than on it.

Glaucoma: Glaucoma is one of the major causes of blindness. High pressure builds in the eye and damages the optic nerve. Any vision that is lost is not repairable.

Cataracts: Cataracts are when the clear transparent lens of the eye develops a cloudy or milky covering. It prevents the eye from being able to see. Although it can happen to young people, it is mostly found in the elderly.

Your eyes are probably your most valuable assets so it is important to take good care of them. Like any other part of the body, a good diet and plenty of rest goes a long way to having healthy eyes.

Now, are you ready to see what you have learned about the eye? Then move on and see if you can find the right answer to the following ten questions.