All About the Eye's Function
The eye, part of our central nervous system, is built along the principles of a camera. A complex series of actions takes place each time we look at an object.
Light rays reflect from the object to the cornea, the "front window" of the eye that transmits and focuses light. Next, the light travels through clear aqueous fluid and through the pupil (the black, circular opening in the center of the iris), which changes size to determine how much light comes in. A transparent lens focuses the rays, which move through the vitreous, a clear, jelly-like substance that fills the middle of the eye.
Finally, when the light rays reach the retina, they appear as an upside-down image. The retina converts this image into electrical impulses that are transmitted along the optic nerve to the brain.
Click the Words on the Diagram for Descriptions
Aqueous Humor
A clear, watery fluid circulating in the chamber of the eye between the cornea and the lens. Common eye conditions related to the aqueous humor include:
- Anterior Uveitis
- Hyphema
- Hypopyon
Cornea
The cornea is the transparent, or clear, front surface "front window" of the eye that covers the iris, pupil, and anterior chamber, providing a protective shield to outside harmful objects like germs, dust and dirt. It transmits and focuses light into the eye.
Similar to the lens of a camera, the cornea provides two-thirds of the eye's focusing power, acting as the camera's focus lens. Because of this, its five layers must be free of any cloudy or opaque areas to allow proper vision.
Iris
The circular, colored curtain of the eye, which opens and closes to regulate the amount of light entering the eye. Common eye conditions related to the iris include:
- Albinism
- Iris Neovascularization
- Iritis
Lens
A transparent structure behind the iris that changes shape to focus light rays onto the retina in the back of the eye. Common eye conditions related to the lens:
Optic Nerve
The nerve that connects the eye to the brain and carries the impulses formed by the retina to the visual cortex. The optic nerve in the brain is about one-and-a-half inches in length, and contains approximately 1.2 million nerve fibers.
A disease of the hypothalamus in the base of the brain, optic nerve hypoplasia (ONH) is today's leading cause of vision loss and blindness in children. Some ONH babies have abnormalities in the brain structure and brain function. Often they also have hormone deficiencies because the pituitary glad, which initiates hormone production, rests at the base of the brain. Such neurological peculi arities can lead to multiple symptoms, including delayed speech, motor skill problems, growth retardation, autistic behavior and seizures.
Under the direction of Mark S. Borchert, MD, the Eye Birth Defects Institute has been researching ONH for more than a decade. Dr. Borchert and his team are uncovering clues about genetic and geographic influences.
Common eye conditions related to the optic nerve include:
Pupil
The dark aperture or opening in the center of the iris which gets bigger or smaller, depending on the light coming in. Common eye conditions related to the pupil include:
- Pupil Anisocoria
- Anterior Synechia
- Coloboma of the Iris
Retina
The retina does a job much like film in the back of a camera. This multilayered, sensory membrane lines the inside back wall of the eye and has the appearance of saran wrap, but is more fragile. It receives light and color and converts them into nerve impulses which go to the brain via the optic nerve.
The retina includes a central macular area and a much larger peripheral area. Two types of photoreceptors - rods and cones - make their home in the retina. There are about 150 million rods, which are sensitive to light, and six million cones, which respond to color. The cones concentrate in the macula, responsible for detailed central vision. We rely on the macula's powers every time we read. Rods are spread throughout the peripheral retina and affect peripheral and night vision. Holding the retina in place and filling the center of the eye is the vitreous humour, a transparent gel.
To function properly, the retina must be attached to the choroid, the thin, blood-rich membrane that lines the inside of the eye.
Common eye conditions related to the retina include:
Vitreous Body
A transparent jelly-like substance, which provides a cushioned support for the rest of the eye and a clear unobstructed path for light to travel to the retina. The vitreous humor, the clear gel in the vitreous body, makes up about 80% of the eye's total volume.
Common eye conditions related to the vitreous body include:
- Vitreous Traction
- Posterior Uveitis
- Vitreous Hemorrhage
| 