Complications of Strabismus Surgery
Squint is the condition of eyes in which they are not properly aligned. It can be congenital or acquired. The reason for Strabismus Surgery is not only for a refractive purpose but also for cosmetic reasons.
It can be caused due to dysfunction of muscles or due to a weakness in the brain.
The treatment is initiated with refractive correction. Along with patching of one eye at a time. The excessive use of the eye can give good exercise for the squinted eye to attain its normal position.
If the above fails, squint surgery is performed depending on the type of squint.
During and after squint surgery certain complications may arise. They are discussed below
If surgery is performed on a visually mature person with acquired strabismus who has diplopia preoperatively. The poor alignment may result in persistent diplopia. Patients with no diplopia prior to surgery may develop diplopia if alignment is not satisfactory.
There is surgical overcorrection in patient with exotropia or overcorrection in an adult patient with decompensated paresis of the fourth nerve. In both cases, the cause of diplopia is the unsuccessful attempt to surgically align the squinting eye.
Patients with constant strabismus may experience diplopia post-operatively with successful alignment. In such cases, patients can’t fuse the image with prism nor the second image be hidden in a suppression scotoma unless the image is shifted optically to the pre-operative location.
The most common diplopia is due to unsatisfactory postoperative alignment. In this situation, diplopia can be eliminated with the use of prisms or further surgery to accomplish the desired ocular alignment.
The use of prisms prior to surgery is to optically stimulate the desired post-operative alignment. It may be helpful in patients who are at the risk of intractable diplopia post-operatively.
Dellen is a shallow excavation at the margin of the cornea that is 1.5–2 mm in diameter. It results due to localized evaporation and dehydration of the cornea.
There is disruption of the tear film and increased compactness of the corneal stromal lamellae.
In post-operative patients, it usually develops within the first 2 weeks and is in common with limbal approach procedure.
Dellen is treated with corneal rehydration that is performed with ophthalmic lubricating ointment. The resolution occurs in a few days to weeks.
Mild Chemosis is routinely seen in post-operative strabismus patients. Severe chemosis can lead to disruption of suspensory attachment of conjunctiva to conjunctival fornix.
Prolonged prolapse of the conjunctiva may result in fusion of the folds, requiring excision.
Treatment options for chemosis are lubricating ophthalmic ointments, topical steroids also subside the condition.
Pyogenic granuloma is a fleshy red mass that has rapid growth. It is a proliferative fibrovascular response to trauma including surgery.
The lesions resolve spontaneously. Many surgeons recommend the use of topical steroids.
Surgical excision may be required for pyogenic granulomas that fail to resolve after topical treatment alone. Recurrence is rare.
Extruded/exposed Tenon’s fascia:
The extrusion or exposure of tenon fascia occurs through the conjunctival incision. It can be avoided with a proper approximation of conjunctival edges during surgery.
Large amount of tenon fascia extrusion should be excised at the end of the surgery. The fascia extruding at the end of the surgery should be excised or extra sutures should be applied.
Topical steroids can be used in cases where excision can’t be performed.
Epithelial inclusion cyst:
Subconjunctival epithelial inclusion cysts occur frequently at the site of conjunctival incision or at the site of new muscle insertion. The epithelial cells deposited during the procedure proliferate and form a cavity resulting in a visible cyst formation.
Anterior segment ischemia:
Anterior segment ischemia is one of the sight-threatening complication of the strabismus surgery. The risk factors include advanced age, previous rectus muscle surgery and history of a vasculopathy, such as diabetes and/or hypertension.
Detachment of three or four rectus muscles at a time result in compromising the vascular supply of the anterior segment in some patients.
Anterior segment ischemia can range from mild to severe and vision threatening.
Mild cases can be demonstrated only with iris angiography while more severe cases may include changes in pupil shape and reactivity, postoperative uveitis, cataract, keratopathy, hypotony and eventual loss of vision and even phthisis bulbi in rare cases.
As the signs are similar to uveitis, many surgeons treat the condition with topical corticosteroids. Oral corticosteroid can be used in more severe cases.
Scleral perforation occurs during reattachment of the muscle to sclera where the needle must carefully penetrate the sclera. It commonly occur during recession surgery.
Scleral perforation may run unrecognized in some cases. It can be recognized with protrusion of uvea or vitreous on tip of suture needle.
Indirect ophthalmoscopy should be performed in suspected cases. In case of a retinal tear, the patient should be closely followed for endophthalmitis and retinal detachment when a perforation is suspected.
Suturing should be done at an alternative position. In addition, antibiotic drops and/or 5% povidone-iodine solution can be applied to the operative site.
Some surgeons will administer subconjunctival antibiotics, a dose of intravenous antibiotics, and/or prescribe prophylactic topical and/or oral antibiotics postoperatively.
Serious post-operative infections are very uncommon following strabismus surgery. Preseptal cellulitis and sub conjunctival abscess are common.
The incidence of endophthalmitis following strabismus surgery is 1 in 350,000 cases suggested in 1962–1 in 18,500 cases suggested in 1992.
Scleral perforation increases the risk of developing endophthalmitis following strabismus surgery.
A subconjunctival abscess should be surgically drained after it is recognized, and the patient started on antibiotics. Affected patients should undergo a dilated fundus examination and slit lamp examination to assess for intraocular infection and should be followed closely for the development of endophthalmitis and orbital cellulitis.
They should be advised of warning signs of these serious potential complications.
The slipped muscle:
A slipped muscle is a disinserted rectus muscle, which, after reattachment to the globe, retracts posteriorly within its muscle capsule, while the empty capsule remains attached to the sclera at the intended new insertion site.
A slipped muscle should be differentiated from a lost muscle in which no portion of the muscle, including its capsule, remains attached to the sclera.
At the time of surgical exploration, the surgeon should anticipate finding the muscle capsule attached to the globe at or near the intended location for muscle placement during the previous surgery.
Once the muscle capsule is located, it is carefully followed posteriorly where the muscle/tendon itself will be found attached to muscle capsule.
The muscle should be isolated, secured with sutures, and brought back in contact with the globe.
The lost rectus muscle:
Unlike a slipped muscle, when an extraocular muscle is lost, no direct attachment remains between the muscle tendon and the globe. The muscle and its capsule both retract posteriorly into the orbit.
A patient with a lost muscle generally presents within hours or days after surgery with a large consecutive strabismus and an associated large duction deficit in contrast to the small duction deficit usually seen with a slipped muscle.
Stretched scar syndrome:
Patients who develop a stretched scar following strabismus surgery may have a similar presentation to patients who have a slipped muscle.
However, the overcorrection with a slipped muscle typically occurs shortly after surgery.
In contrast, overcorrection in stretched scar syndrome usually occurs several months later. At the time of reoperation, an amorphous scar tissue separating the muscle tendon from the scleral attachment site is generally found.
It is postulated that scar lengthening after surgery is responsible for the recurrent deviation.