Exotropia (divergent squint)

What is exotropia?

Exotropia, or divergent squint, refers to an eye that turns or diverges outwards. Exotropia may occur from time to time (intermittent exotropia) or may be constant. You may only notice one particular eye drifting out, or it may be either eye that deviates, known as an alternating exotropia.

These types of exotropia usually begin in early childhood. Congenital exotropia is more unusual, and often indicates poor vision or an ocular pathology.

 

What is intermittent exotropia?

Some people have a tendency for their eyes to drift outward when their eyes are completely relaxed, such as when they are “staring off into space”, or when looking in the far distance. This outward drift, which occurs only in those moments of visual inattention, can be controlled when visual attention is refocused. The exotropia may occur rarely and result in few or no symptoms.  However, in some people it may become more frequent or even progress to the point of becoming constant.

 

 

                   

    Intermittent exotropia in the right eye

 

 

What are the signs of intermittent exotropia?

People with intermittent exotropia may experience an outward drift only occasionally, such as when they are very tired, feeling sick, or after drinking alcohol, despite their efforts to refocus. Some patients may experience double vision (diplopia); others say that they can feel that an eye is misaligned, even though they do not see anything unusual. Others are unaware that an eye is turning, unless another person mentions it to them.

Why does my child, who has intermittent exotropia, close one eye frequently?

Children with intermittent exotropia commonly close or squint one eye at times, especially when they are exposed to bright sunlight. The exact reason for this is not clear. Small children who won't wear sunglasses may be offered a hat with a brim, such as a baseball cap, to shield the eyes from the sun, thereby limiting the need to close one eye.

Will having an intermittent exotropia affect my child’s eyesight?

In many cases where the exotropia only occurs infrequently, then often there is no effect on the child’s eyesight. If the exotropia becomes more constant, then the deviating can become under-used and amblyopia (reduced vision) may develop. It is important therefore to have regular vision checks with your orthoptist. If amblyopia develops your orthoptist may recommend patching or an atropine regime. Of course, if your child is shortsighted or longsighted this should be corrected with glasses.

Can anything be done to keep intermittent exotropia from getting worse?

Keeping the child as well rested and healthy as possible will help. Feeling sick or having a fever may cause the intermittent exotropia to temporarily occur more frequently.

Your orthoptist or ophthalmologist may recommend eye exercises or minus (concave) lenses if they feel your child will benefit.

Exercises involve improving the child’s ability to convergence their eyes and/or training them to become more aware of when their eyes are deviating so that they can learn to control it better.

Minus lenses (glasses with a prescription such as -1 or -2 etc.) stimulate the eyes to focus harder. As the eyes focus (accommodate) they also converge (turn in) which helps to control the divergent angle. Eventually the child would be weaned off the glasses in the hope that they can maintain control of the exotropia themselves.

 

This child wears concave lenses to control his exotropia

 Concave lenses controlling an exotropia

In cases where the exotropia persists after exercises and minus lenses, then strabismus (squint) surgery may be required. Children who undergo surgery at an older age may have better outcomes and treatment. Exercises or minus lenses can help to keep their eyes working together until they are an optimum age for surgery. Your orthoptist and ophthalmologist will discuss the ideal timing of surgery for your situation.

What is binocular vision?

Binocular vision refers to the brain's ability to see objects with both eyes simultaneously. It is only possible when the eyes are straight and not when the exotropia is present. Among other benefits, binocular vision is necessary for normal depth perception, or "3-D vision". Children who are capable of maintaining binocular vision are also less likely to develop amblyopia.

What is sensory or deprivation exotropia?

Exotropia in an eye with very poor vision is called sensory exotropia. In this case, the eye with low vision is unable to work together with the other eye, and therefore, the poorly-seeing eye may have a tendency to drift outward.

Sensory exotropia may occur at any age. Of course, if the visual problem is treatable, it should be addressed as soon as possible. Surgery to cosmetically straighten the eye may be possible.

What age is best for exotropia surgery?

Age is not the main determining factor for exotropia surgery. The surgery is appropriate when exotropia is worsening and is present for the majority of the time. However older children may have better long term outcomes.