How the Eye Works

Eyes are amazing and complex. To understand the nature of vision problems, you must first understand how the eye works. Every part of the eye performs a special function. If any part of the eye cannot do its job properly vision is disrupted.

The Process
Light reflects off of objects and into our eyes. This light passes through the cornea, pupil and lens and is focused on the retina. The retina transmits the image to the brain through the optic nerve. When the brain receives and interprets the image, we have sight.

Cornea
The cornea is the clear outer part of the eye. When light passes through the cornea it is bent (refracted) to focus on the retina. The cornea is responsible for two-thirds of the focusing function of the eye.
Pupil and Iris
The pupil is the opening which controls how much light enters the eye. The iris is the colored part of the eye. It contains the muscles which open and close the pupil. In low light the pupil dilates, or opens very wide, to let in as much light as possible. In bright light the pupil closes down as tiny as possible to reduce the amount of light that enters the eye.
Lens
The lens is located just behind the pupil and is responsible for one-third of the focusing function of the eye. The lens is what changes focus between near and far objects. This adjustment is called accommodation.
Retina
On the inside wall of the back of the eye is the retina which contains photoreceptor cells. Light is focused on these cells, and they send the information to the brain through the optic nerve. The macula is the center of the retina, and is responsible for detecting fine details and color.
Refractive Error
The shape of the cornea and the distance between the cornea and the retina determine whether or not the light will focus on the retina as it should. A misshapen cornea or misshapen eye causes refractive error, meaning that the light is not bent like it needs to be to focus properly on the retina. LASIK surgery can correct the shape of the cornea, or change the shape of the cornea to compensate for a misshapen eye. This corrects refractive error by adjusting the focal point to the retina, where it should be.

Myopia (nearsightedness)
When the cornea is curved too much or the eyeball is too long, light focuses in front of the retina, and has spread back out by the time it reaches the retina.
Hyperopia (farsightedness)
When the cornea is too flat or the eyeball is too short, the focal point is behind the retina, so the light is still spread out when it reaches the retina.
Astigmatism
The eye is shaped like a football and creates multiple focal points, instead of one, making the image blurry.
Presbyopia
With age the lens of the eye becomes stiff, or the muscles which control the lens become weak or stiff, and accommodation is diminished or lost. Fine adjustments in focus are no longer made by the eye. This is why people develop the need for reading glasses as they age. LASIK surgery for monovision can adjust the focus of one eye for objects up close and the other eye for objects in the distance. With a little practice the brain automatically chooses the proper image.
The entire eye must be working together properly to accomplish vision. Even the slightest imperfection can impair vision. Many of these imperfections can be corrected, and clear vision restored.

If you are experiencing vision problems, talk to your ophthalmologist today.