WHAT IS A SQUINT?
A squint is a misalignment of the eyes – also known as strabismus. There are various types of squints, the most common being a horizontal misalignment with the eyes deviating inwards – a converging squint or esotropia. A squint can also deviate outwards – a divergent squint or an exotropia. A squint can also be vertical. An eye that deviates upwards is called a hypertropia and an eye that deviates downwards is called a hypotropia.
WHAT CAUSES A SQUINT?
There are several causes which include: hyperopia (far sightedness), poorly functioning eye muscles and poor function of the nerves that allow eye movement. More often we believe the underlying problem lies in a part of the brain and for some people there is difficulty in keeping the eyes aligned.
TREATMENT OF A SQUINT
In many young children wearing the correct prescription glasses is all that is required. However, many children and adults need an operation to put the eyes straight. Eye exercises are useful for a very particular type of squint known as an exotropia with convergence insufficiency. This is not common. In all other instances we do not believe eye exercises to be of value in the treatment of squints.
One or both eyes might be operated on even if only one eye appears to be squinting. Under general anaesthetic the muscles responsible for moving the eyes are strengthened or weakened by repositioning them. Dissolvable stitches are used to place the muscles in new positions on the surface of the eyeball. Lasers are not used in this surgery and the eye is never removed from the eye socket. Squint surgery can be performed at any age.
In adults and older children an adjustable suture technique might be used. Once the patient is fully awake after the operation, the eye positions can be evaluated and, if necessary, changed if the eyes are not straight. This is done with the patient awake. The adjusting process is well-tolerated as anaesthetic drops are used at the time of muscle adjustment. The adjustment usually takes place about 4 to 5 hours after the operation.
RISKS OF SURGERY
The risks of squint surgery are very low. The risks include:
- Double vision – patients may experience this after the operation because of the change in position of the eyes. This is not common and goes away spontaneously in 90%.
- Infection of the surface of the eye – 1 in 50. This is readily treatable.
- Inflammation around the stitches – 1 in 50
- Infections within the eyeball – 1 in 5000
- Damage to the eyeball from suture needles – 1 in 1000
- Loss of vision due to any of these complications – 1 in 30 000
Overall, squint surgery leads to straight eyes in about 80%. 20% will need another operation and half of those will need a third operation. Success rates differ between the various types of squint. Over the lifetime of a patient with a squint, the average number of operations required is between 3 and 4. A deviation in eyes that was initially straight after the operation can occur years or decades down the line.