Common Visual Conditions Causing Blurred Vision
Myopia
Myopia or nearsightedness is a refractive condition in which near objects are seen clearly while distant objects are blurred. There are many optical elements in the eye: the cornea, the lens, and the fluids between them. These all combine in such a way to image the outside world onto the back of the eye, or retina.
Infants are typically born farsighted and over the first 2 years of life, the optical elements of the eyes change until a slightly farsighted (hyperopic) refractive error or no refractive error (emmetropia) remains. Later in life myopia can develop if the eyeball becomes too long and objects come to a focus in front of the retina. Since the eyeball can not be shortened, glasses or contact lenses are prescribed; these change the optics coming into the eye so that light comes to a focus on the retina. In addition to glasses or contact lenses this can also be done by manipulating the shape of the cornea through refractive surgery or a procedure utilizing contact lenses, called orthokeratology.
Environmental and Genetic Influences in Myopia Development
About 25% percent of the general population in the U.S. are nearsighted. While it was once believed that myopia was inherited, recent evidence suggests that there are both genetic and environmental influences. For instance, myopia is found more often in identical twins than fraternal twins suggesting a strong genetic influence. Yet indicators of environmental influences include: a higher prevalence of myopia in urban vs. rural communities, in graduate or professional degree students vs. high school or college graduates, and in certain occupations that require a lot of near work, such as clinical microscopy.
When Myopia Can Occur or Progress
Myopia rarely develops before 6 years of age; it more commonly occurs at about age 10 years. However, some people don’t develop myopia until their 20’s, often when they enter college or graduate school. On occasion, some people first develop myopia in their 30’s and even in their 40’s. In addition, some childhood-onset myopes stop progressing by age 18 years while others continue into their 20’s, 30’s and 40’s.
It is still unknown why some people develop myopia while others do not, and why it first occurs at different ages and why sometimes it progresses and at other times does not. What is known is that both environment and hereditary play a role. At the Eye Care Clinic, various treatment options are offered which have promise for slowing down myopia progression.
Hyperopia
Hyperopia or farsightedness occurs when the eyeball is too short or the cornea has too little curvature, so that light entering the eye is focused behind the retina. While focusing is required to see near objects clearly, persons with a hyperopic refractive error also have to focus for far objects. Thus, by using the focusing system some farsighted people can see clearly without glasses. Often, they may not even know they are farsighted. However, if there is a significant amount of hyperopia, then the constant focusing often will tire their eyes. They will have even more trouble with near work because of the extra work their eyes have to do. Hyperopia can be corrected with glasses, contact lenses, and corneal reshaping techniques such as refractive surgery which focus the light rays onto the retina.
Environmental and Genetic Influences in Hyperopia Development
Most infant eyes start out hyperopic and become emmetropic (no refractive error or slightly hyperopic refractive error) at about age 2 years. It is normal to have a small amount of hyperopia. It is likely that the visual environment in those first 2 years of life allows the fine tuning necessary for the eye to become emmetropic. However, large amounts of hyperopia in infancy often result in a continued hyperopic refractive error later in life.
When Hyperopia Can Occur
Unlike myopia, hyperopia rarely progresses. However a hyperopic person may need stronger glasses as he/she get older. This is because as we age, our focusing system becomes less efficient and therefore harder to rely on it as much to see clearly without the use of corrective lenses.
Some children are farsighted and don’t know it. They don’t realize that they are working harder than others just to get things clear. Unfortunately, school screenings often fail to detect farsightedness. Children with uncorrected hyperopia may avoid near work or do poorly at near related tasks. Common signs of farsightedness include difficulty in concentrating and maintaining a clear focus on near objects, eyestrain, fatigue and/or headaches after close work, aching or burning eyes, irritability after sustained concentration. All children should have a vision examination before starting school.
(Pediatric Vision Examinations)
Astigmatism
Astigmatism is a vision condition that occurs when the surfaces of the cornea, the front part of the eye and/or the lens are not exactly spherical or perfectly round. This results in preventing a perfect focus on the back of the eye. With astigmatism, vision may be blurred at all distances. If the astigmatism is mild, blur may not be noticed. However, headaches, or sore or tired eyes may be a symptom of uncorrected astigmatism. With more severe astigmatism, vision will be noticeably blurred.
Almost all levels of astigmatism can be optically corrected with eyeglasses and/or contact lenses. Corneal modification through orthokeratology or refractive surgery is also a treatment option for some patients.