If the patient still has a convergent strabismus and troublesome double vision after 6-12 months surgery may be considered.

The aims of surgery are:

• To reduce the angle of the convergent strabismus
• To enlarge the area of binocular vision
• To improve the range of eye movements

If the eye is able to move outwards normally or nearly normally, the convergent strabismus is treated by weakening the medial rectus muscle and strengthening the lateral rectus muscle. This surgery is usually carried out using an adjustable stitch technique.

If there has been little or no recovery of the outward movement of the eye strengthening the lateral rectus muscle will not be effective. Instead the two vertical eye muscles, the superior and inferior rectus muscles, are reattached alongside the lateral rectus muscle. This type of surgery is known as transposition surgery. In their new position these muscles are able to help move the eye outwards, to a more central position, whilst still being able to move the eye upwards and downwards. An injection of Botox to the medial rectus muscle is normally carried out at the same time.

It can take up to 2 months to have the maximum effect from transposition surgery. Although this type of surgery is very successful in reducing the size of the convergent strabismus the outward movement of the eye is usually still limited.

Common complications of surgery are:

• Sometimes it is not possible to completely eliminate all double vision and a prism may be needed to correct any small residual strabismus.
• The convergent strabismus can recur once the botox has worn off. If this happens further botox treatments can be given or surgery can be carried out to permanently weaken the medial rectus muscle. The reason why we avoid doing this at the time of the original surgery is because operating on three muscles of the same eye will disrupt the blood supply to the front of the eye causing it to become very inflamed. However, after 6 months the blood supply has recovered and it is safe to operate on a third muscle.

Republished, with permission, from www.squintclinic.com.