The most well-known part of a comprehensive eye exam is the basic vision test. When you have a general vision test, one of the main conditions the eye care practitioner is checking for is a refractive error. A refractive error means there is an abnormality in the shape of the eye, changing the eye’s ability to focus light directly onto the retina.This causes blurred vision and can usually be corrected by wearing prescription eyeglasses, contact lenses and possibly, alternate treatments such as vision therapy, ortho-k, LASIK or refractive surgery such as LASIK.
The term, “refractive error” refers to a problem with the process of refraction that is responsible for sight. Normally, light rays that enter your eye are refracted or bent through the cornea and the lens, and ultimately converge or are focused onto a single point on the retina. From the retina, messages are sent through the optic nerve to the brain which then interprets these signals into the image that we are seeing.
In order for this process to work effectively, the anatomy of the eye including the length of the eye and the curvature of the cornea and the lens must be just right to be able to focus the light onto the retina. When this is not the case, a refractive error will occur.
There are several different types of refractive errors, depending on which part of the eye is affected, and it is possible to have multiple refractive errors at the same time:
Myopia or nearsightedness:
In myopia the length of the eyeball is too long which results in light coming to a focus in front of the retina, rather than on the retina. This allows the individual to see well when objects are close but not clearly when looking at objects at a distance.
Hyperopia or farsightedness:
Hyperopia is when the eyeball is shorter than normal and can result in near objects being blurry. However, people experience hyperopia differently. Sometimes distant objects are clear while other times people may experience overall blurred vision near and far or no problems at all. In children particularly, the lens may accommodate for the error allowing for clear vision but may cause fatigue and sometimes crossed eyes or strabismus. Hyperopia causes eyestrain or fatigue especially when looking at near objects for a period of time. Often people with 20/20 vision may still need glasses at their desk to relax their eyes and improve concentration.
Astigmatism is usually the result of an irregularly shaped cornea (although it can sometimes also be due to a misshapen lens). The cornea, which is normally round, is more football-shaped in an eye with astigmatism, resulting in multiple focus points either in front of the retina or behind it (or both). People with astigmatism usually have blurred or distorted vision to some degree at all distances, near and far.
Presbyopia is an age-related condition which usually begins to appear sometime after 40. As the eye begins to age, the lens stiffens and can no longer focus clearly on objects that are close.
It’s important to note that presbyopia is often confused with hyperopia, as both cause problems focusing at near distances. However, high hyperopia can also cause blur at far distances as well, especially in dim lighting, and depth perception problems can result in motor vehicle accidents. In these instances people with hyperopia could use glasses at any distance.
If you are having trouble seeing, it is important to have an eye exam to determine the cause of the problem and to effectively correct your vision. Even if your vision is fine, you should schedule a routine eye exam on a regular basis to ensure that your eyes are healthy and that any potential problems are caught early.
Sometimes a person is unable to produce enough tears or their tears do not possess the right qualities to keep eyes healthy and comfortable. This can cause a consistent lack of sufficient lubrication and moisture on the surface of the eye, known as dry eyes.
Normally, the eye constantly lubricates itself with tears by producing them at a slow and steady rate, keeping itself moist and comfortable. Usually these tears consist of three layers, an oily, a watery, and a mucus layer. Each layer has a specific role in lubricating your eyes. The oily layer is outermost. It’s main purpose is to slow evaporation of the tear. The watery layer is in the middle. This makes up the majority of what a person normally thinks of as tears. This layer cleans the eye and helps to wash away small foreign objects and particles. The inner layer consists of mucus. This mucus allows the watery layer to stick to the eye and spread evenly over the eye in order to keep it lubricated. In a person with dry eyes, either hormonal changes, side effects from medication or some other factor causes the eye to either not produce enough tears, or leave out parts of the tear that make proper lubrication possible.
Dr. Mark A. Rasmussen, of Ultimate Eyecare Santa Fe, in Santa Fe, New Mexico, explains, “Symptoms of dry eyes include stinging or burning in the eyes, scratchiness, and excessive irritation from smoke or wind. Although it may sound counter-intuitive, the eyes’ response to the consistent irritation caused by dry eyes may also cause a person to experience excessive tearing. In this case, the eye is attempting to flush and lubricate itself by producing more tears, but is unable to do so successfully due to the rate of evaporation or inability to spread the tears properly.”
Although dry eyes are not always curable, your optometrist may prescribe artificial tears to help with some of the symptoms. Artificial tears are lubricating eye drops that may help with dry, scratchy feeling eyes. Different artificial tears work in different ways. Some help replenish parts of the tear that your eyes are not producing on its own, others help to produce more tears overall. Your eye doctor will assist you to choose which will help you most. Dr. Rasmussen cautions, however, “These artificial tears should not be confused with eye drops that are advertised to ‘get the red out.’ These eye drops may indeed reduce the appearance of redness in your eyes, but this is accomplished by making the blood vessels in your eyes smaller rather than actually lubricating your eyes. As such, these drops can sometimes actually make your symptoms worse. One should also be aware that if you wear contacts, some eye drops require you to take them out before using the drops and wait 15 minutes or more before reinserting your contact lenses.”
Some cases of dry eyes are seasonal, such as those which occur as a result of cold, dry winter air. In this case, your eye doctor may recommend wearing sunglasses or goggles when outdoors to reduce your eyes’ exposure to the sun, wind and dust. For indoors, your optometrist may recommend an air cleaner and humidifier to take dust out of the air and add moisture to air which is too dry.
Studies have also shown that nutrition may have a part in helping to relieve some symptoms of dry eyes. Your eye doctor may recommend nutritional supplements such as omega-3. Good sources of omega-3 fatty acids are cold-water fish, cod, herring and salmon, as well as flaxseed oil. Mild dehydration can make symptoms worse too, so be sure to drink plenty of water, 100 percent fruit and vegetable juices and milk.