A condition in which the visual axes of the eyes are not parallel and the eyes appear to be looking in different directions. In divergent strabismus, or exotropia, the visual axes diverge. In convergent strabismus or esotropia, the visual axes converge. The danger with strabismus is that the brain may come to rely more on input from one eye than the other, and the part of the brain circuitry that is connected to the less-favored eye may fail to develop properly, leading to amblyopia (weakened vision) in that eye. The classic treatment for mild to moderate strabismus is to cover the stronger eye with a patch, forcing the weaker eye to do enough work to catch up. Atropine eyedrops can also be effective in correcting moderate lazy eye. Severe strabismus may require surgery. Also known as lazy eye.
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Types of strabismus
There are several different types of strabismus, including a lazy eye.
There are different types of strabismus. They can be described by the cause or by the way the eye turns.
The following terms describe strabismus by the positions of the eye:
- Hypertropia is when the eye turns upwards
- Hypotropia is when the eye turns downwards
- Esotropia is when the eye turns inwards
- Exotropia is when the eye turns outwards
An early diagnosis of strabismus will enable more effective treatment. In the past, it was thought that after a “critical period”, strabismus could not be treated.
While treatment up to the age of 6 years is believed to be most effective, strabismus can be treated at any time.
Six different muscles surround each eye and work “as a team.” This allows both eyes to focus on the same object.
In someone with strabismus, these muscles do not work together. As a result, one eye looks at one object, while the other eye turns in a different direction and looks at another object.
When this occurs, two different images are sent to the brain — one from each eye. This confuses the brain. In children, the brain may learn to ignore (suppress) the image from the weaker eye.
If the strabismus is not treated, the eye that the brain ignores will never see well. This loss of vision is called amblyopia. Another name for amblyopia is “lazy eye.” Sometimes lazy eye is present first, and it causes strabismus.
In most children with strabismus, the cause is unknown. In more than one half of these cases, the problem is present at or shortly after birth. This is called congenital strabismus.
Most of the time, the problem has to do with muscle control, and not with muscle strength.
Other disorders associated with strabismus in children include:
- Apert syndrome
- Cerebral palsy
- Congenital rubella
- Hemangioma near the eye during infancy
- Incontinentia pigmenti syndrome
- Noonan syndrome
- Prader-Willi syndrome
- Retinopathy of prematurity
- Traumatic brain injury
- Trisomy 18
- Diabetes (causes a condition known as acquired paralytic strabismus)
- Graves disease
- Guillain-Barré syndrome
- Injury to the eye
- Shellfish poisoning
- Traumatic brain injury
- Vision loss from any eye disease or injury
The symptoms of strabismus are the effects that are noted by the patient and may include:
- Double vision
- Decreased depth perception
- Jittery vision
- Eye strain
The brains response to the double vision that results from strabismus is to block out the vision of the weaker eye. This is beneficial in that the patient is able to see and focus on objects more easily, but is associated with a decreased ability to gauge depth. Over time, many individuals are able to compensate for this by using monocular cues to judge depth.
The treatment of strabismus depends on the specific signs and symptoms experienced by the patient. The severity and impact on quality of life also guide the treatment decisions.
The initial step in the management of the condition typically involves the prescription of glasses, if needed. Following this, treatment of the abnormal eye may be required to improve vision, which usually consists of vision therapy, such as the wearing of a patch or eye exercises. In some cases, surgery to the eye muscles may be required if other therapies do not offer adequate improvement to vision.
Eyepatches can be used to try and correct strabismus. Image Credit: galitsin / Shutterstock.com
Eyeglasses or contact lenses
It is common for patients with strabismus to suffer from farsightedness, particularly those with esotropia, which can be corrected by wearing glasses or contact lenses.
This is the first step in the management of the condition, and some patients may find that their symptoms improve entirely with this simple step, such as those with mild esotropic strabismus. The corrective lenses help the eyes to focus on objects with less effort, which improves their ability to remain aligned correctly.
Prism lenses are sometimes prescribed to change the light that enters the eye, which reduces the distance the eye needs to move to focus on objects in the field of vision. This helps to improve the symptoms of strabismus because the eyes are able to focus more easily, thus reducing the degree of turning of the eye.
Vision therapy may include a number of different exercises and activities that are designed to improve the movement, coordination and focus of the eyes. It aims to train the eyes and brain to work together more coherently, improving the vision and reducing the symptoms of the condition.
A common exercise that helps to improve the symptoms for many patients is to wear a patch over the normal eye. This forces the “lazy” eye to work harder in order to allow the individual to see properly. After the eye has been “trained” the patch can be removed and both eyes are often aligned more closely.
Eye exercises can improve abnormalities of the eyes and encourage healthy alignment. These should be practiced on a regular basis and adults with the condition may need to continue these exercises indefinitely.
Eye muscle surgery
Surgical procedures can be used to manipulate the length and positioning of the muscles in and around the eyes to improve the alignment of the eyes. The methodology involves changing the functionality of the muscles in the eyes to alter the alignment of the eyes. It is a relatively short procedure that can be completed within an hour.
This procedure can help to improve symptoms and is sometimes the only method that can help patients to improve the cosmetic appearance of the condition, which affects the individual’s confidence and willingness to participate in social activities.