Describe the surgical treatment of squint with its complications.

Types and Techniques

• Squint surgery alters the mechanical balance of the muscles, and rests on three manoeuvres:
• Weakening procedures — recession, in which the muscle is detached and reattached posterior to its original insertion, reducing its effective pull; myectomy, chiefly of the inferior oblique; tenotomy; and the FADEN (posterior fixation) suture, which anchors the muscle to the sclera well behind the insertion and selectively weakens it in its own field of action without altering the primary position — useful in convergence excess and in dissociated vertical deviation
• Strengthening procedures — resection, in which a segment of muscle is excised and the muscle reattached at its original insertion, effectively shortening it; plication, which folds the muscle rather than cutting it and is reversible and preserves the anterior ciliary vessels; and advancement

Complications and Applied Aspects

• Under-correction and over-correction are much the commonest complications; a proportion of patients require a second operation, and this must be part of consent
• Consecutive deviation — an exotropia following esotropia surgery, or the reverse; it may appear months or years later
• Slipped or lost muscle — the muscle retracts within its capsule or is lost posteriorly. It presents with sudden marked limitation of movement in the immediate postoperative period and is a surgical emergency, since a lost muscle retracts further with time and becomes progressively harder to recover
• Scleral perforation — the sclera is thinnest just behind the insertions (0.3 mm); perforation risks vitreous haemorrhage, retinal detachment and endophthalmitis, and requires examination of the fundus and often retinopexy
• Anterior segment ischaemia — from interrupting too many anterior ciliary arteries. Each rectus carries two except the lateral rectus, which carries one; so operating on three or more recti in one eye at a single sitting is avoided, particularly in older patients and in vasculopaths. It presents with anterior chamber inflammation, corneal oedema and iris atrophy, and can lead to phthisis. Muscle-sparing techniques and plication reduce the risk
• Infection — conjunctival infection, orbital cellulitis and rarely endophthalmitis
• Adherence syndrome from fat prolapse and scarring, restricting movement
• Conjunctival scarring, cysts, granuloma and dellen; and change in lid fissure height, since recession of a rectus tends to widen the fissure and resection to narrow it — which matters cosmetically