Common Vision Conditions
We are happy to provide you with some basic information on several common vision conditions:
Amblyopia, commonly called lazy eye, occurs when one eye develops differently than the other eye, causing one eye to have poorer visual acuity than the other. Sometimes a difference in refractive error (especially hyperopia) causes one eye to be used more often. Other times, the eyes are misaligned, causing one eye to “shut off” to avoid double vision. Regardless of the cause, the result is a weakened, or amblyopic eye, that is unable to be corrected to 20/20 vision with glasses or contacts.
It’s hard to spot amblyopia. Sometimes a child will noticeably favor one eye over the other. Another possible symptom is the child frequently bumping into things on one side. The best way to tell if your child has lazy eye is through a complete exam at about six months and three years. Early diagnosis is extremely important and can prevent amblyopia from leading to more serious problems, such as loss of the ability to see three dimensions or functional blindness in the amblyopic eye.
Most of the time amblyopia cannot be entirely corrected. However, with treatment, vision in the amblyopic eye can be improved to some extent. Treatment involves encouraging the weak eye to develop. This is done using eye patches, vision therapy, glasses, contact lenses, or a combination of the four. The strong eye may be patched to encourage the weak eye to develop. Vision therapy can help to correct improper use of the eyes. If a focusing error is at the root of the problem, then glasses may reduce the error. Most of the time the amblyopic eye will always require glasses.
Sometimes the cornea is irregularly shaped, causing the eye to focus an object on two different areas of the retina. This is known as astigmatism. For the cornea to bend light correctly, it should be dome-shaped, like a basketball. Astigmatic corneas are shaped more like a football. Uncorrected astigmatism causes blurred vision at all viewing distances and can lead to squinting, eyestrain, and headaches.
The cause of astigmatism is unknown. Astigmatism is often associated with myopia or hyperopia, and it usually is present from birth. It may be hereditary, or it may be caused by factors such as pressure on the cornea, incorrect posture, or increased use of the eyes for “near work.”
Mild astigmatism usually does not need to be corrected. Eyeglasses, contact lenses, or refractive surgery can correct moderate to high degrees of astigmatism.
When rays are focused correctly on the retina of a relaxed eye, the eye is said to be emmetropic. Emmetropia is the medical term for 20/20 vision, vision that needs no corrective lenses, contact lenses, or reading glasses. It occurs because the optical power of the eye can perfectly focus an image to the retina, giving it “perfect” vision.
The opposite of emmetropia is ametropia. With ametropia, the focal point of the eye is some distance in front of or behind the retina. The following vision conditions are types of ametropia.
Hyperopia is more commonly known as farsightedness. As the name suggests, people with farsightedness are able to focus on objects that are further away, but have difficulty focusing on objects that are very close. This is because the eyeball is shorter than normal, which causes light rays entering the eye to have a focal point behind the retina. About a fourth of the population is farsighted.
A family history of hyperopia is a risk factor for developing hyperopia. Most babies are born hyperopic but they usually outgrow the condition as their eyes develop into the correct shape.
Hyperopia can be corrected with eyeglasses or contact lenses. There are also new surgical procedures that can correct hyperopia.
Myopia is the medical term for what most people call nearsightedness. It is a condition in which a person can see objects clearly only when they are close; when objects are farther away it is difficult to focus on them. Myopia usually develops in early childhood, although it sometimes develops in early adulthood. In rare cases, myopia can lead to more serious conditions such as retinal detachment.
Myopia is considered a genetic disorder. If your parents are nearsighted, you are at greater risk of also being nearsighted. Another driving factor of myopia is excessive “near work” – work involving fine detail or focusing on close objects.
Myopia can be corrected with eyeglasses or contact lenses. Myopia tends to increase the most between the ages of 8 and 12 years old. Studies have shown that orthokeratology, the use of topical atropine, and multifocal contacts, can help to slow the progression of myopia. Myopia can also be corrected by LASIK surgery.
As we age we naturally lose the ability to accommodate. Accommodation is the eye’s ability to change its focal point from distance to near. In the early to mid 40’s a condition called presbyopia sets in. This usually manifests itself with difficulty reading and eyestrain with near work. Progressive addition lenses (PALs), bifocals, multifocal contacts, or reading glasses are a way to address this condition.
Presbyopia is a natural consequence of the aging process. Even if someone has never had vision problems before, they can still develop presbyopia. It may seem to occur suddenly, but it actually occurs over a long period of time. Symptoms include having to hold things at arm’s length to see them clearly, eye strain, fatigue, and headaches from near work.