Squint surgery involves moving the muscles of the eyes to a new position in order to change the alignment of the eyes.
Each eye has six muscles that normally work in unison to keep the eyes correctly aligned. The muscles we most frequently operate on are the horizontal muscles called the medial and lateral rectus muscles. These muscles are responsible for the side to side movement of the eyes. The rectus muscles are found just under the surface of the conjunctiva, which is the transparent layer of tissue covering the white outer coat of the eye. The muscles attach to the outer coat of the eye 5-7 mm behind the edge of the cornea (the clear window of the eye).
The two oblique muscles are mainly involved with vertical and rotational movements of the eyes and are attached to the back of the eyeball.
Squint surgery is usually carried out under a general anaesthetic as a day-case procedure. Occasionally surgery can be carried with the patient awake by numbing the eye with local anaesthetic injections, or with local anaesthetic drops and intravenous sedation.
It is a common misconception that the eye needs to be removed from its socket to carry out squint surgery, it does not! Before surgery the eye is cleaned with an antiseptic solution and the eyes and face are covered with a sterile drape. A small opening is then made in the drape and the eyelids are held open using a small clip.
To find the eye muscles the conjunctiva is opened either close to the cornea or beside the muscles themselves. The muscles are then identified and the sleeve of tissue surrounding the muscle is cleaned away from the muscle.
Before each squint operation the ophthalmologist will have made a plan regarding which muscles need to be strengthened or weakened and by how much. Which eye muscles are operated on and how much they are strengthened or weakened will depend on the type of squint, how large the squint is and whether squint surgery has been carried out in the past. This is why it is so important to have accurate measurements of the angle of the squint, as Ophthalmologists use these measurements to calculate how many millimeters each muscle should be weakened or strengthened by.
In the case of a convergent squint, the eyes can be straightened by either weakening the medial rectus muscles of both eyes or by strengthening the lateral rectus muscle of one eye and weakening the medial rectus muscle of the same eye.
To make the eye more comfortable as the patient wakes up many surgeons will inject some local anaesthetic around the eye muscles or put some local anaesthetic drops on the surface of the eye, at the end of the operation. This means that the eye muscles will also be weakened temporarily and as a result it is not uncommon for the squint to look worse in the first 3-4 hours after the surgery!