ABOUT THE EYE

Some people liken the eye to a camera. As light passes through the lens, it is bent and transposed onto the eye’s film: the retina. The film is then ‘developed’ by the brain, becoming the image that we see. In order for an individual to have perfect vision, all components of the eye must be functioning properly. Otherwise, eye diseases and refractive errors can lead to impaired vision. Read the sections below to learn more about how the eye functions, its structures, and the eye diseases and refractive errors that result in imperfect vision.
How the Eye Functions
As light enters the eye, it first passes through the cornea, the clear outer portion of the eye. Because the cornea is curved, the light rays bend, allowing light to pass through the pupil to the lens. The iris, or colored part of the eye, regulates the amount of light that enters the eye with the ciliary muscles. These muscles cause the pupil to contract when exposed to excess light or to dilate when there is too little light.
When light hits the curved surface of the lens, it is refracted and brought into focus on the retina. The retina then turns the light into electrical energy. This energy passes through the optic nerve to the brain stem and finally into the occipital lobe, where it is converted into an image.
The Eye’s Structures
Cornea - The clear surface of the eye where light rays refract as they pass through to the pupil.
Iris - The colored part of the eye that controls the amount of light that passes through the pupil.
Pupil - An open space in the center of the iris where light passes through to the lens.
Lens - The part of the eye that refracts light to focus it properly on the retina.
Retina - The structure at the back of the eye that converts light rays into electrical energy that is transferred to the optic nerve.
Optic Nerve - The biological pathway to the brain stem, which forwards electrical energy to the occipital lobe.
Occipital Lobe - The part of the brain that converts electrical energy into an image.
Eye Diseases and Refractive Errors
The process described above occurs flawlessly in people with 20/20 vision. However, vision can be impaired when the shape of the eye is irregular or when the light rays do not focus properly on the retina. These flaws are known as refractive errors. Imperfect vision can also occur as a result of various eye diseases. Learn more about the refractive errors and eye diseases that cause vision problems.
Refractive Errors
Refractive errors can be treated with LASIK surgery, custom LASIK, or other laser vision correction procedures, including PRK and LASEK. The following refractive errors can impair vision:
Nearsightedness (myopia) - Nearsighted vision is caused by an irregularly shaped cornea that results in light focusing in front of the retina, rather than directly on the retina. People who are nearsighted have difficulty seeing objects at a distance.
Farsightedness (hyperopia) - Farsighted vision is caused by an irregularly shaped cornea that results in light focusing behind the retina instead of directly on the retina. People who are farsighted have difficulty seeing nearby objects.
Astigmatism - The most common of all eye disorders, astigmatism is a condition in which the eyeball is shaped more like a football than its naturally spherical shape. This odd shape causes light to focus on two points of the retina, rather than one.
Presbyopia - Presbyopia occurs when the lens of the eye becomes less flexible, necessitating the use of reading glasses for near vision. Specifically, the lens becomes stiffer, and the muscles that control the lens become weaker, hindering its ability to bend and flatten in order to focus light on the retina.
Eye Diseases
Cataracts - A cataract is a condition characterized by a clouding of the eye’s natural lens. This clouding occurs when protein begins to clump together in the lens.
Glaucoma - Glaucoma is an eye disease that occurs when elevated intraocular pressure (IOP) causes damage to the optic nerve.
Macular degeneration - Macular degeneration is a degenerative eye disease that is characterized by a loss of central vision. It occurs when the macula (a tiny area on the retina) becomes damaged.
Diabetic retinopathy - Diabetic retinopathy is a degenerative eye disease that occurs in patients with diabetes and is characterized by abnormal blood vessel growth. This can eventually lead to a detached retina and blindness.