What exactly is strabismus?

Strabismus is one of the many terms in ophthalmology that causes confusion and mix-up. Revered London-based consultant ophthalmologist, Professor Chris Hammond clearly defines what strabismus is and distinguishes it from other conditions, such as ‘lazy eye’.

What is strabismus?

Strabismus, which is also colloquially known as squint, is a disorder characterised by the misalignment of the eyes. For example, when someone with strabismus attempts to look ahead, their eyes actually look in different directions. 

What are the different types of strabismus?

Strabismus is a catch-all phrase. There's a wide range of strabismus, but what they all have in common is either the eye deviates from the straight head position or sees double. Strabismus can be convergent, where the eyes move inwards, divergent, where the eyes diverge outwards, but also sometimes there is a vertical imbalance between the eyes.

Often children have strabismus and that's quite commonly associated with being long-sighted, that's called an accommodative squint. Strabismus affects adults too, particularly those who either had a lazy eye as children or have neurological problems, such as nerve palsy where the muscles of their eyes are not moving properly due to nerve damage or sometimes due to disease in the muscles themselves. 

How does strabismus differ from other eye conditions like lazy eye, amblyopia, and squint?

People often get a little confused by the terms, which is understandable because there are so many. When we talk about a lazy eye in ophthalmology, we're talking about, in technical terms, amblyopia and that means that the vision is reduced in one eye, even with glasses. That usually arises because during childhood the eye had strabismus or didn't focus properly and as a result, the brain did not develop the normal pathways for vision. Strabismus quite commonly accompanies amblyopia or lazy eye.

Squint is just another word we use for strabismus, meaning the eyes are not moving correctly together. In everyday language, we use the verb ‘to squint’ to mean screwing up the eyes to see clearly or in bright light for example and that's not what we mean by strabismus. Strabismus or squint means the eyes not working together properly and a lazy eye means that the vision is reduced in one eye. 

What are the causes of strabismus?

There are various causes of strabismus, such as genetic and environmental factors, from childhood all the way up to adulthood. One of the challenges of strabismus is firstly working out the cause and then secondly the challenge of working out how best to correct it.

We see some children developing strabismus in their first year of life, called infantile esotropia, resulting in their eye turning inwards. We don't fully understand why it happens. In part, it's a sort of miswiring of the eye muscle pathways from the brain.

Most commonly, we see strabismus during childhood associated with long-sightedness, and this often runs in families, but not always. Kids who are long-sighted tend to over-converge their eyes because they're trying to bring their focus near and that gives them strabismus. This can be treated often with glasses.

Strabismus can be due to neurological problems, such as a stroke or even a brain tumour, or due to muscle diseases, like thyroid eye disease or myasthenia gravis. There’s an increase in people who are myopic (short-sighted) developing a double vision when they look in the distance.

How is strabismus treated, and which treatment is most effective?

Strabismus is treated by a variety of methods. In children, it may be treated with glasses or with surgery on the eye muscles. In adulthood, sometimes we'll treat it with what's called a prism which can be built into glasses, bending the light, so people don’t see double.

It can also be treated with Botox injections. Even though Botox is now used in the aesthetics industry to reduce wrinkles, it was actually invented by an eye surgeon for eye muscles. It is injected into the eye muscles, weakening them to make the eyes work better together. More commonly, surgery on one or more of the eye muscles is needed to straighten the eye.

If you or your child have developed strabismus and would like to find out more about the disorder or treatment options, book a consultation with highly-experienced Professor Chris Hammond directly by visiting his Top Doctors profile.