Strabismus - Misaligned or Crossed Eyes
Sometimes called as crossed-eyes, walleye (or squint), strabismus is a vision problem in which both eyes do not look at the same point at the same time. In other words, strabismus is misalignment of the two eyes that prevents the individual from being able to aim both eyes at the same object for proper focus.
According to estimates, about 7% of children between the ages of 6 and 17 years have some type of eye turn. Of these about 80% have an eye turning inwards and 20% have an eye turning outwards.
It is perfectly natural as a parent for you to feel anxious and a little upset by the fact that your child has misaligned eyes. Aside from the obvious cosmetic concerns, you may notice that your child doesn’t perform certain visual and eye-hand tasks as well as expected.
Common age for strabismus
Strabismus most often begins in early childhood. However, it is not uncommon to see cases of strabismus in adolescents and people of mature age.
What puts you or your child at the risk of strabismus?
- Genetic tendency: A family history of strabismus
- Existing vision problems: Farsightedness, cataract
- Muscle and nerve disorders: Multiple sclerosis, myasthenia gravis, or cerebral palsy
- Tumor in the brain or eye
- Premature birth, low birth weight, birth injury, or newborn problems
- Trauma: Head injury
- Infections: Such as meningitis or measles
- Down’s syndrome
What are the causes of strabismus?
Family history (genetics): There is often a strong family tendency towards eye turns (47%). This means there’s a genetic factor that may have made your child predisposed to developing the condition.
Refractive error: A significant refractive error. This means that one or both eyes are very longsighted or shortsighted. Simply stated the child has a focus problem not an eye muscle problem. The brain focuses the eyes on objects to see things clearly which results in stimulation of the muscle, which pulls the eyes in. Often this type of turn is first noticed when the child is becoming more involved in close work (ages 2 to 4 years).
Mechanical injury or disease: In some cases, inward turning is caused by a mechanical restriction (e.g., fibrosis of muscle tissue) or a physical obstruction (e.g., blowout fracture) of the external eye muscles. Adults may develop strabismus from eye or blood vessel damage, loss of vision, an eye or brain tumor, Graves' disease, stroke, and various muscle and nerve disorders.
Surgery: In some cases, poorly or incompletely performed surgery may lead to subsequent and progressive inward turning of both eyes.
High accommodative convergence ratio: Some individuals seem to have an excessive stimulation of the inner muscles that pull the eye inwards when the eyes try to focus. This is called a high accommodative convergence ratio. Hence, even with relatively low degrees of long sightedness or little near work demand the eyes get excessive stimulation for an inward position. Eventually the brain learns to leave one eye in and turn it off to alleviate the stress and demand of pulling both eyes out.
What happens in strabismus?
Normally, the small muscles surrounding each eye work together to move both eyes in the same direction and at the same time. However, when these eye muscles do not work properly to control eye movement, you are said to have strabismus. When the eye muscles do not work correctly, the eyes may become misaligned, and the brain may not be able to merge the two images.
How would you know if you have strabismus?
The most prominent sign of strabismus in children is that their eyes do not look at the same point in space at the same time. Some children may also report blurred vision, tired eyes, and sensitivity to light. Double vision (diplopia) may also occur when strabismus first occurs.
In addition, squinting, closing one eye in bright sunlight, and tilting or turning the head to look at an object may also indicate strabismus.
How does strabismus affect your child?
First of all, you should remember that having strabismus probably doesn’t worry your child very much. They are not in any pain or discomfort and often they can’t understand what all the fuss is about. This is because when the eyes are misaligned, the brain ignores one of the images it receives so that your child isn’t seeing double. Sometimes when the problem is first developing the child will get double-vision intermittently but the brain generally adapts very quickly.
However, while the child is likely experiencing no discomfort, treatment should be sought as soon as possible. By only using one eye, the child loses some important aspects of vision, such as depth perception. In addition, if the brain's suppression of one eye occurs long enough, the eye that’s being ignored won’t function as well in terms of eyesight (seeing clearly), eye movement skills, or eye processing (perception) abilities. This is called amblyopia ("lazy eye") and this will need to be treated first before we can get the brain to pay attention to that eye.
How your doctor diagnoses strabismus
Your eye doctor can often tell that you or your child has strabismus just by looking at the eyes. It may be apparent that the eyes do not look in the same direction at the same time.
Your doctor may have you look at an object while covering and then uncovering each eye. This allows your doctor to find which eye turns, how much it turns, and under what circumstances the abnormal turn occurs. These tests will also help your doctor determine if you (or your child) also have amblyopia (lazy eye) in which one eye is not used enough for the visual system in the brain to develop properly.
Is there any treatment for strabismus?
Indeed, yes! Your doctor may recommend the use of glasses, patches, medicines and/or surgery either to control or completely cure the problem.
Eye glasses: Wearing glasses can sometimes correct strabismus when the condition is mild i.e. your eyes are only slightly misaligned. Glasses can be even more effective when combined with vision therapy. In face, research suggests that in about 80% of cases, this combination will achieve a functional cure.
Eye (visual) training: Eye or visual training is about teaching your child how to straighten their eye and developing the mechanism by which they can maintain the eyes straight. It is not something you do to the patient but rather something you do with the patient. A child is never too young for visual training. Just the type of training will be different at different ages. For a very young child training will be applied to help prevent some of the adaptations the brain will make to eye turned such as amblyopia. This, with the application of spectacles, is sometimes all you have to do to help the young child to develop normal binocular vision. The majority of cases however will need more than this with visual training therapy over 6 to 18 months before stale binocular vision is established.
Eye patches and medicine: Depending on the cause and severity of your strabismus and if it “co-exists” with amblyopia, using an eye patch and medicines may significantly help resolve both conditions. You should remember that often resolving amblyopia may help the eyes to align because they would be used equally, allowing them both to focus on one object. In some cases, eye exercises may be helpful.
Surgery: Surgery is the last alternative to consider in achieving a functional cure for your child’s eye turn. It does not aim to treat the underlying reason for the eye turn but rather focuses on lengthening or shortening the muscle of the eye in the hope of straightening the eye. If your child has a congenital eye turn or a true muscle defect then surgery may be recommended very early. Unfortunately your child will still only have a small chance of achieving a full functional cure. Research has also shown that there is little advantage in having this surgery prior to 12 months of age. In other cases when there is a very large degree of turn, which is not responding well to spectacle, lenses and visual training then surgery may also be utilized. These cases do not have as high success rate in achieving a functional cure. This success rate however is further improved by post surgical training. About 30% of all children who have eye surgery require multiple surgeries (2 to 3 operations). Finally, with any surgery there is a degree of risk. One child every 2 years dies on the operating table having eye surgery (in USA).
Will your child outgrow strabismus?
A child rarely outgrows strabismus once it has developed. Without proper and timely treatment, strabismus can lead to permanent vision problems such as the development of poor vision in the eye which already has strabismus. This condition is called as lazy eye or amblyopia.
If your newborn's eyes are not aligned at birth, they should become aligned by 3 to 4 months of age. In some cases, the eyes may simply seem to be misaligned because the child has a wide bridge of the nose that creates the appearance of crossed eyes (pseudo-strabismus).
However, if your child is older than 4 months and his / her eyes are not aligned all of the time, he (or she) should have an eye exam by an ophthalmologist as early as possible.
Are amblyopia and strabismus the same? (Removing the confusion)
Because of the lack of proper knowledge and awareness, both the terms “amblyopia (lazy eye)” and “strabismus” are often used synonymously. However, in reality, both terms and conditions (while often related to each other) are different.
By definition, amblyopia is the loss of one eye's ability to see details.
Strabismus, on the other hand, is a “misalignment of an eye” which causes the eye to lose focus on a target. As a result, the brain may ignore the signals coming from that eye and this can lead to amblyopia of that eye.
Amblyopia can be caused by a pre-existing strabismus, although it can be caused by many things and not just strabismus. Hence, strabismus can lead to amblyopia, but many cases of amblyopia do not have strabismus and are therefore not noticeable, even to the most observant parent.
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