Strabismus

Strabismus is also known as squint, cross-eyed or a turn in the eyes. Strabismus is where both eyes do NOT sit straight, they are misaligned and do not work together. Strabismus is when a person looking at an object, has one eye that focuses on the object and the other eye is looking somewhere else. Strabismus may be constantly present or appear intermittently. Strabismus that is unilateral affects one eye. Strabismus that affects both eyes, where the strabismus switches from one eye to the other is known as alternating. If the misalignment of the eyes is small it is known as small angle strabismus, if the misalignment is large, it is known as large angle strabismus.

Patients with strabismus develop double vision; this is because the turned eye sits away from the normal primary position, the brain cannot fuse the two very different images seen by both eyes, due to the turn in one eye. To prevent double vision (diplopia) the brain ‘switches the turned eye off’ and ignores it, the visual development of that eye ceases. This can lead to amblyopia, known as lazy eye, where the vision is poorer in the turned eye than the non-turning eye.

Strabismus is usually detected in early childhood, with early detection; the vision and strabismus can be treated. This will give the child a more successful visual outcome. Some patients may develop strabismus in adulthood but this is normally caused by another eye or health problem, this would need to prompt investigation & treatment too.

One eye turning in: is known as an EsoTropia.

One eye turning out: is known as an ExoTropia.

One eye turning up: is known as a HyperTropia.

One eye turning down: is known as HypoTropia.

If the turn in the eye switches from one eye to the other, this is called alternating.

• Turn in the eye – misalignment of the eyes

• Poorer vision in one compared to the other (amblyopia)

• Intermittent double vision (if the strabismus is intermittent)

• Headaches

• Eye strain

• Fatigue when reading or concentrating

• Unstable vision, vision feels jumpy when concentrating

• Other people will notice that your eye turns when you are tired, stressed, day dreaming or concentrating

If there is a large strabismus present, double vision may not be noticed as the brain ‘switches the turned eye off’ because the turn in the eye is too large to correct by itself. Patients with a large strabismus may not experience any fatigue, eyestrain or headaches as the brain has learnt to completely ignore the turned eye. Patients will have significantly poorer vision in the turned eye compared to the non-turned eye.

We all have 6 eye muscles attached to each eye eternally; these are called the extraocular muscles. These muscles receive signals from the brain to control the movement, direction and position of the eye. For normal vision development both eyes must work together perfectly in their position, functioning and neurological (nerve signal from the brain) control.

Strabismus occurs when the nerve is damaged creating poor transmission of nerve signals to the eye muscle, if there is a problem in the brain control center that directs your eye movements or you have an impaired eye muscle. Strabismus is when the control and function of the eye muscles (extraocular muscles) is disrupted.

Strabismus can occur from an eye injury or health conditions such as stroke, Downs syndrome, head injury and cerebral palsy.

If a parent has strabismus, their child is at a greater risk of developing strabismus.

If you have uncorrected hypermetropia (hyperopia or long sighted) prescription this may also cause strabismus. A type of strabismus called Accommodative esotropia often occurs because of uncorrected hypermetropia, once correction is given via glasses or contact lenses the strabismus is corrected.

• Glasses or contact lenses are used to correct your eye prescription. This will help you see clearly and may correct the strabismus (accommodative esotropia). Sometimes glasses and contact lenses are the only treatment suitable and required of the strabismus

• Prism lenses in your glasses alter the way light enters the turned eye and reduces or eliminates the turn in the eye.

• Vision therapy eye exercises (Orthoptics) given to you by your Orthoptist or Optician can help with vision development in the turned eye, focusing of the turned eye, brain-eye connection and get both eyes to work as a team. These eye exercises help train the brain and eyes to work together.

• Another vision development technique is patching. The good eye is patched to make the turned eye’s vision develop better or to a similar level as the good eye.

• Strabismus surgery is surgery of the eye muscle. Tightening of the eye muscle and/or the re-positioning of the eye muscle is changed to make the turned eye appear straight or sit straight. Patients that have strabismus surgery will also need eye exercises to help both eyes work together as a team. Surgery alone will not eliminate amblyopia (poor vision in one eye).