There are quite a few similar disorders in the strabismus category, but exotropia and esotropia cover specific cases where one eye deviates inward or outward. With exotropia one of the eyes turns outwards, and with esotropia one turns inwards.
How to remember which is which?
Refer back to the Greek origins of the words – “exo” meaning exit or way out – can act as a prompt for you.
How is it caused?
Eye movements are controlled up and down by four muscles, and side to side by two muscles, so only six in all. If just one of those muscles doesn’t function correctly the eyes misalign and messages sent to the brain are misinterpreted.
Causes of the disorder are not really understood, although children suffering from other disorders including Down syndrome and cerebral palsy often exhibit symptoms.
The most common form of exotropia – intermittent exotropia – is found in young children up to the age of seven. Obviously young children are not able to discern what they are experiencing compared to other children, nor are they able to explain adequately what they experience; children in such instances often start to close one eye for improved vision as well as rub and “squint” their eyes.
Other types of exotropia include:
Physiologic exotropia – found in the normal population, but only to a minor degree within the parameters of sight variation. New born children may show signs but the effects clear up quickly within a few months without any further concerns.
Convergent insufficiency exotropia – someone who has started off with esotropia (with an eye turning inwards) may develop an exotropic version in adolescence. Adults can also develop this version if surgery has been used and there has been some overcompensation.
Sensory exotropia – if an eye is partially blind it may slowly begin to turn outwards.
Congenital exotropia – in this case the exotropia is present at or even before birth; genetic abnormalities may be a cause, but environmental factors may have an effect.
There are two types of treatments – surgical and non-surgical.
• Non-surgical treatments are usually tried initially and include the use of spectacles with a bigger minus effect, or patches.
• Surgical treatments – better long term success is possible when surgery is used in cases of intermittent exotropia, which is remember the most common form of the disorder.
The question of when to use surgery can be answered using the simple rule: “consider surgery if the condition is there for more than half the day or is slowly getting worse”.
The surgical process involves a day procedure with a small cut made to gain access to one of the two muscles that control sideways movement. The patient usually recovers quickly, but may need to wear prescription spectacles for a while.
In the case of convergence insufficiency exotropia it has been found that treatment through optometric vision therapy (eye exercises) by a behavioural optometrist can be effective, although some mainstream optometrists find such methods controversial.