Why Does Strabismus Occur?

Strabismus, also known as crossed eyes, is caused by the two eyes failing to maintain proper alignment. This means that when you’re looking at something, one eye looks directly at the object while the misaligned eye looks in a different direction. This can be inwards (esotropia), outwards (exotropia), upwards (hypertropia) or downwards (hypotropia), depending on the type of strabismus you have. Not everyone who suffers from strabismus has it all the time – it can be an intermittent problem that sometimes affects just one eye or both interchangeably. So, what causes this condition, and can it be treated?

Symptoms of Strabismus

The main sign of strabismus is the visible misalignment of the eyes. When this misalignment is really obvious, it’s known as ‘large-angle’ strabismus which refers to the angle of deviation between both eyes. Smaller deviations are referred to as ‘small-angle’. While it may seem contradictory, it’s actually small-angle strabismus that causes the most noticeable visual symptoms for the individual, including headaches, eye strain and an inability to read comfortably. In children, these side effects can cause difficulties in learning and their academic development if left untreated.

However, large-angle strabismus doesn’t usually cause these symptoms as there is virtually no attempt from the brain to try and align the eyes. Both of the conditions can take their toll on the self-esteem and psychological impact of the patient though. It can lead to embarrassment, awkwardness, ridicule from others and difficulty in keeping eye contact with other people.

The best way to detect strabismus is through routine check-ups throughout childhood. Babies' eyes are usually intermittently crossed because their vision is still developing, but strabismus doesn’t disappear as the child grows. The earlier the condition is detected, the easier it is to treat so making sure your child has regular eye tests is the best way to monitor their eye development and pick up on any problems early on.

What Causes Strabismus?

The eye has six external muscles, known as the extraocular muscles, which control the positioning of the eyeball and how it moves. For normal binocular vision, this positioning and neurological control have to be coordinated perfectly. But, for people with strabismus, there are issues with the anatomical or neurological control of the eyes that means the extraocular muscles don’t function as they should. Genetics often play a part in this, with children of someone with strabismus more likely to develop it themselves. It can also occur when a child who is far-sighted tries to compensate for their inaccurate vision by developing a form of strabismus called accommodative esotropia. This can develop later in childhood but it’s most common in children below two years of age and can be corrected with glasses or contact lenses, toric contact lenses from Acuvue (moists for astigmatism).

How is it Treated?

There are two ways of treating strabismus – with surgical treatments or vision therapy. In most cases, opticians will refer children with strabismus to a specialist ophthalmologist who specialises in this field and can suggest the appropriate type of surgery. It’s not just an effective treatment for children though, as many adults with long-term strabismus find that it effectively aligns their eyes. If you don’t want to go down the surgical route, there is an alternative. For intermittent and small-angle strabismus, vision therapy is an option.

Vision therapy is an effective treatment for convergence insufficiency, a specific type of intermittent exotropia where the eyes struggle to align when looking at objects close to them. Strabismus surgeons may suggest a course of vision therapy for a set period of time to treat amblyopia (a term for ‘lazy’ eyes) and minor vision problems that might still be present after surgery.