Eye Basics (See our eye disorder animations below)
Actually, the eye doesn’t see, the brain does. The eye admits rays of light and focuses that light into a perfect point on the retina—the thin membrane of rods and cones at the back of the eye. These photoreceptors then convert that light into nerve impulses that travel through the optic nerve to the brain.
Light enters the eye through the pupil—the black, round opening in the center of the iris—the colored part of the eye. The pupil opens (dilates) in dim light to admit more light. In brighter light, the pupil gets smaller (constricts) to limit the amount of light entering the eye. The iris controls the pupil and determines the color of your eye. A heavily pigmented iris results in a brown eye, while a lightly pigmented iris results in a blue or gray eye. The iris is surrounded by the sclera—the tough, white, outer wall of the eye.
Myopia (Nearsightedness)Nearsighted individuals typically have problems seeing well at a distance and are forced to wear glasses or contact lenses. The nearsighted eye is usually longer than a normal eye, and its cornea may also be steeper. Therefore, when light passes through the cornea and lens, it is focused in front of the retina. This will make distant images appear blurred. There are several refractive surgery solutions available to correct nearly all levels of nearsightedness.
Farsighted individuals typically develop problems reading up close before the age of 40. The farsighted eye is usually slightly shorter than a normal eye and may have a flatter cornea. Thus, the light of distant objects focuses behind the retina unless the natural lens can compensate fully. Near objects require even greater focusing power to be seen clearly and therefore, blur more easily. LASIK, Refractive Lens Exchange and Contact lenses are a few of the options available to correct farsightedness.
Asymmetric steepening of the cornea or natural lens causes light to be focused unevenly, which is the main optical problem in astigmatism. To individuals with uncorrected astigmatism, images may look blurry or shadowed. Astigmatism can accompany any form of refractive error and is very common.
Astigmatism can be corrected with glasses, contact lenses, corneal relaxing incisions, laser vision correction, and special implant lenses.
Presbyopia is a condition that typically becomes noticeable for most people around age 45. In children and young adults, the lens inside the eye can easily focus on distant and near objects. With age, the lens loses its ability to focus adequately. Although presbyopia is not completely understood, it is thought that the lens and its supporting structures lose the ability to make the lens curvature greater during close vision effort. To compensate, affected individuals usually find that holding reading material further away makes the image clearer. Ultimately, aids such as reading glasses are typically needed by the mid-forties. Besides glasses, presbyopia can be dealt with in a number of ways. Options include: monovision and multifocal contact lenses, monovision laser vision correction, and new presbyopia correcting implant lenses.
