The main aims of surgery are:

1. To reduce the angle of the vertical strabismus
2. To reduce the size of the head posture
3. To enlarge the area of binocular vision

Surgery to weaken the inferior oblique muscle, by either removing a segment from the muscle or changing the position it attaches to the eyeball is the most commonly performed operation for a superior oblique palsy.

In 80% of congenital palsies a successful outcome is achieved with this single operation.

Significant complications following inferior oblique surgery are very uncommon. The vast majority of patients experience little or no redness or discomfort of the eye and return to normal activities within a week of surgery.

If the inferior oblique muscle has only been partially weakened the vertical strabismus and in particular the tendency of the eye to drift upwards when looking to the opposite side, can persist. Occasionally further surgery to the inferior oblique muscle is required to correct this.

If excessive bleeding occurs during inferior oblique surgery scarring can develop some weeks or months after the surgery. This scarring makes it difficult for the patient to move their eye upward, resulting in troublesome double vision. This double vision can be difficult to treat even with further surgery. However, the risk of excessive bleeding causing this complication is less than 1%.

If the patient is unable to control their vertical strabismus a prismatic lens can be stuck to the glasses to reduce the angle of strabismus. As a rule prisms are used to treat small strabismuss when surgery is not being contemplated or as a short-term measure in larger strabismuss.

Further surgery could be needed if:

• The patient still has a small area of single vision and is troubled by double vision when they look downwards and / or to the side.
• There is troublesome torsional double vision, with objects appearing to be twisted to one side. This type of double vision cannot be corrected with prisms in glasses.
• The patient still needs to use a large head posture to maintain an area of single vision.

Further surgery normally involves strengthening the superior oblique muscle itself, either by putting a tuck in the entire muscle tendon or just strengthening the front fibres of the tendon, this is known as an Harada-Ito procedure (named after two Japanese strabismus surgeons).

The superior oblique tuck operation is very successful in correcting a vertical strabismus, which is worse when the patient looks downwards. It will also correct torsional double vision. An inevitable consequence of this type of surgery is some limitation of the upward movement of that eye, but most patients do not find this troublesome.

The Harada-Ito procedure is used to treat torsional double vision when there is not much of a vertical strabismus. This operation can be done using an adjustable stitch so that the surgery can be fine tuned with the patient awake after the operation.

It is quite common for patients to have superior oblique palsies on both sides as a result of a head injury. These patients frequently need a combination of superior oblique tucks and Harada-Ito procedures to correct their torsional double vision and restore a useful area of single vision.

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