What is a refractive error?
In normal vision, light enters the eye through the cornea and is focused at a single point on the retina at the back of the eye. With a refractive error, there is a defect in the way light passes through the eye. Light rays do not refract, or bend, properly to achieve a single focus point. Instead, light rays focus in front of the retina (nearsighted), behind the retina (farsighted), or at two different points (astigmatism). Refractive errors usually result from a defect in the length of the eye or shape of the cornea.
Nearsightedness, farsightedness and astigmatism result when the cornea, the very front clear portion of your eye is too steep or too flat or when the eye itself is too long or short. These refractive errors cause the light rays passing through the cornea and lens to come into focus before or beyond the retina. The result is blurred vision.
Myopia, or nearsightedness, is the result of an eye that is too long or a cornea that is too curved. In both cases, light rays entering your eye fall short of the retina and objects in the distance appear blurred. If you have this condition, you are not alone. Over 70 million people in North America have myopia.
Hyperopia, or farsightedness , is the opposite of myopia. With Hyperopia, the eye is too short or your cornea is too flat. As a result, light rays entering your eye fall behind the retina. This results in blurred vision which is worse at near distance than far.
Astigmatism is a condition in which the surface of the cornea is not spherical. Images appear blurred or ghostlike because light rays are refracted unequally. In extreme cases, images both near and far appear blurred. Many people that have myopia also have astigmatism.
Presbyopia occurs as you reach your 40s or 50s. The crystalline lens inside your eye loses its elasticity, making it more difficult to read smaller print. Laser Vision Correction does not alter the lens of your eye and does not correct this problem. However, there are procedures that can be performed with Laser Vision Correction such as monovision that can assist patients with presbyopia.
Think of the eye as a camera. The iris acts like the shutter, regulating the amount of light entering the eye. The retina functions like the film and is the surface upon which light must be exactly focused. This retinal image is then transmitted to the brain where the picture the eye receives is recognized. The cornea, combined with the lens, provides the focusing power that controls the clarity of the image.
For more information on common vision problems and how to correct them, contact the eye experts in Sacramento and Roseville, California. Call Griffin & Reed Eye Care at (916) 485-2020 or, if you are interested in LASIK, book a LASIK evaluation online.