Refractive Eye Errors
Refractive eye errors are the most common vision disturbances and affect approximately 150 million Americans to some extent. Refractive errors are caused by disturbances in the way the eye focuses light. If the light rays do not focus exactly on the retina, an error occurs and vision is affected. There are four basic types of refractive errors – hyperopia, myopia, astigmatism and presbyopia.
Hyperopia is the ophthalmologic term for farsightedness. Individuals suffering from this type of refractive error usually experience a blurring of the visual field up close, as well as eye pain or discomfort when reading, working on a computer or focusing vision up close for extended periods of time. Hyperopia vision distortion occurs because light is focused behind the retina, rather than on it. It is often genetic and may be present from birth. However, this type of refractive error is easily corrected with corrective lenses or refractive surgery.
Myopia – or nearsightedness – is the opposite of hyperopia, in that light is refracted in front of the retina, rather than behind it. Because of this, individuals with myopia usually experience blurred vision at a distance rather than up close. The condition is usually not present at birth, but rather develops during the school years as the eyes develop and grow. People with myopia usually squint to see things far away or compensate for sight impairment by sitting closer to the TV or at the front of the class. Although myopia tends to worsen over time, most people “stabilize” before age 30. Nearsightedness is usually treated with corrective lenses, although many patients elect to undergo refractive surgery to permanently correct the condition once it stabilizes.
Astigmatism is a refractive error caused by an abnormal curvature of the cornea. A normal cornea is round and globe-like, but a cornea with astigmatism may be more rounded in some areas than others. Individuals with astigmatism may experience blurred near and distant vision, as well as related symptoms like eyestrain and headaches. Astigmatism can be addressed with corrective lenses when necessary, or it may be treated with laser refractive surgery.
Presbyopia is very common refractive error associated with aging. Individuals with this condition may begin to hold objects away from the face in order to better focus on them. This is because presbyopia occurs as the eye loses the ability to focus on close objects, such as books or pictures. Although presbyopia is a very normal part of aging, it is an annoyance to many. It usually begins between ages 40 and 50 and may continue to worsen for up to 25 years. Most people with presbyopia who have otherwise good eyesight will compensate for the refractive error by using over-the-counter reading glasses. Prescription bifocals, trifocals or monovision lenses are available to presbyopia patients who have other preexisting refractive errors. Surgical options are also available for permanent sight correction.