Eye alignment and coordination play a large role in development of the visual system. Here we will discuss several binocular vision problems that can have a life long affect on vision.
Strabmismus (Eye Turn)
Strabismus is a condition that occurs when the eyes aren’t properly aligned with one another, resulting in one eye turning in, out, up or down with respect to the other eye. When the eyes are not working together properly, as is the case with strabismus, abnormal binocular vision will result. While the most obvious symptoms of this would be double vision or diplopia, smaller amounts of miscommunication between the eyes’ muscles can cause decreased depth perception, eye strain, and headaches. There are various conditions that can result in strabismus including the imbalance of extraocular muscles (often from birth), vascular problems (stroke, diabetes, hypertension, TIA, etc), and compressive lesions within the brain or visual pathway (mass, tumor, etc).
Treatment for Strabismus
Treatment for strabismus is determined by the underlying cause. If present from birth, a combination of eyeglasses, vision therapy, and/or surgery to “straighten” the eyes can be very effective. Often times, strabismus is accompanied by amblyopia. If acquired due to a medical condition, the treatment is based upon addressing the underlying cause, and then working with the patient to alleviate any lasting visual problems that are present afterward. If acquired in the later stages of life, strabismus is often simply due to the muscles that control the eye alignment wearing down. This often results in double vision that can usually be minimized by using special glasses that use prisms to direct the light entering the eye such that double vision is eliminated while wearing the glasses.
Also known as “lazy eye”, amblyopia is a condition that results in best corrected vision that is reduced from normal levels, even with the optimal prescription in glasses. This condition can affect one or both eyes and develops during childhood. Since there is very little vision at birth, the brain forms connections to the eye during the first several years of life but this process can be disrupted if there is not a normal picture coming from the eye. This process of abnormal visual development can occur for a number of reasons including refractive, strabismic, or deprivation amblyopia.
Refractive amblyopia occurs when there is a large or very unequal amount of refractive error (glasses prescription) present at birth. One of the most common scenarios is when one eye is normal (little or no glasses prescription required) and the other eye is born very farsighted. In this scenario, a child will see clearly with both eyes open and rarely complain of problems because their brain is paying attention to “the good eye”, which is providing clear vision. Often times the farsighted eye, or “bad eye” will develop strabmismus, and begin to turn out or in, which prompting an evaluation by an optometrist. The reason that an “eye turn” develops in the farsighted eye, or “bad eye” is because the connections between the eye and the brain (where vision is processed) are not being adequately formed due to the constant blurry vision as seen through that eye. As these connections fail to form, the extraocular muscles can begin to weaken and become unable to hold the eye in its correct position.
Strabismus amblyopia occurs when a child is born with strabmismus or “eye turn”. Our brains are designed to be extremely adaptive when we are young as we are learning how to perceive the world around us. Due to this fact, if an eye is turned out, or turned in, the brain will suppress vision in that eye. If the brain were to acknowledge the vision provided by the “turning eye”, double vision would be experienced as one eye is pointed at what we intend to look at and the “turning eye” is pointed toward another object. As the brain suppresses the vision from the strabismic, or “turning” eye, the connections between the eye and the brain (where vision is processed) begin to fail. As these connections fail, the result is a decrease in vision, even while wearing glasses.
Deprivation Amblyopia develops when a child has a condition, such as a congenital cataract, that deprives the eye of vision. If an eye is deprived of vision, the proper development of the connections between the eye and the brain (where vision is processed) will not form, and vision is decreased.
Treatment of Amblyopia
It is important to identify and treat amblyopia as early in life as possible. The prognosis/efficacy of treatment is greatly improved if started before the age of 7. The visual pathway continues developing from birth, through age 7 – 8. It is during this time (from birth to age 7-8) that the connections between the eye and brain (where vision is processed) can be strengthened. After age 8, amblyopia may be resistant to treatment as the visual pathway has already completely developed.
The treatment of amblyopia is directed to improve vision by strengthening the weaker amblyopic eye. This can be done with a combination of full time glasses, patching, or sometimes eye drops. Full time glasses wear is important so that the amblyopic eye is given the prescription that produces the best vision (which is often still reduced) at all times for the affected eye. Often times, wearing glasses is not enough to improve vision of an amblyopic eye. If this is the case, a patch can be worn over the “good eye”, per the directions of your eye doctor, in order to force the brain to pay more attention to the amblyopic eye. As the brain pays more attention to the affected eye, the essential connections between the eye and the brain can be improved, resulting in better vision for that eye. In some cases, an eye doctor may prescribe eye drops that can be used to make vision blurry in the “good” eye to achieve this same result.