Strabismus surgery, also known as extraocular muscle surgery, eye muscle surgery, or eye alignment surgery, is surgery on the extraocular muscles to correct strabismus, a misalignment of the eyes. Strabismus surgery is a same-day procedure that is usually performed under general anesthesia most commonly by either a pediatric ophthalmologist. Some general ophthalmologists and Neuro-ophthalmologists are also trained to do strabismus surgery. The patient usually spends only a few hours in the hospital with minimal preoperative preparation. After surgery, the patient should expect soreness and redness but is generally free to return home.
History The earliest successful strabismus surgery intervention is known to have been performed on 26 October 1839 by Johann Friedrich Dieffenbach on a 7-year-old esotropic child; a few earlier attempts had been performed in 1818 by William Gibson of Baltimore, a general surgeon and professor at the University of Maryland. The idea of treating strabismus by cutting some of the extraocular muscle fibers was published in American newspapers by New York oculist John Scudder in 1837.
Indications Strabismus surgery is one of many options used to treat any misalignment of the eyes, called strabismus. This misalignment or "crossing" of the eyes can be caused by a variety of issues. Surgery is indicated when other, less invasive methods have been unable to treat the misalignment or when the procedure will significantly improve quality of life and/or visual function. The type of surgery for a given patient depends on the type of strabismus they are experiencing. Exodeviations are when the misalignment of the eyes is divergent ("crossing out") and esodeviations are when the misalignment is convergent ("crossing in"). These conditions are further categorized based on when the misalignment is present. If it is latent the condition is called a "-phoria" and if it is present all the time it is a "-tropia". Esotropias measuring more than 15 prism diopters (PD) and exotropias more than 20 PD that have not responded to refractive correction can be considered candidates for surgery.
Techniques
The goal of strabismus surgery is to correct misalignment of the eyes. This is achieved by loosening or tightening the extraocular muscles in order to weaken or strengthen them, respectively. There are two main types of extraocular muscles - rectus muscles and oblique muscles - which have specific procedures to achieve the desired results. The amount of weakening or strengthening required is determined through in-office measurements of the eye misalignment. Measured in PD, the size of the deviation is used along with established formulas and tables to inform the surgeon how the muscle must be manipulated in surgery.
Rectus muscle procedures The main procedure used to weaken a rectus muscle is called a recession. This involves detaching the muscle from its original insertion on the eye and moving it towards the back of the eye a specific amount. If after a recession the muscle requires more weakening a marginal myotomy can be performed, where a cut is made part way across the muscle. The procedures used to strengthen rectus muscles include resections and plications. A resection is when a portion of the muscle is cut away and the new shortened muscle is reattached to the same insertion point. A plication on the other hand is when the muscle is folded and secured to the outer white portion of the eye, known as the sclera. Plication has the advantages of being a quicker procedure that involves less trauma than a resection and preserves the anterior ciliary arteries - the latter of which minimizes the risk of blood loss to the front of the eye allowing for operation on multiple muscles at one time. Studies on horizontal rectus muscle surgeries have shown that both procedures have similar success rates and no difference in post-operative exodrift or overcorrection rate was discovered. However, further investigation is required to determine if there is any difference in long term effects from the two procedures. Because of the antagonistic pairings of the rectus muscles and the fact that strabismus can be a binocular problem, in certain cases surgeons have the option of operating on either one eye or both eyes. For example, a study published in 2018 compared the outcomes of bilateral lateral rectus recession and unilateral recession/resection of the later/medial recti for intermittent exotropia. This study showed that the unilateral procedure had higher success rates and lower recurrence rates for this specific condition. This is not necessarily true for all types of strabismus and further investigation is required to reach a consensus on this particular aspect of the surgery.
Oblique muscle procedures There are two oblique muscles attached to the eye - the superior oblique and the inferior oblique - which each have their respective procedures.
Inferior oblique The inferior oblique is weakened through a recession and anteriorization where the muscle is detached from the eye and reinserted at a spot anterior to the original insertion. Some surgeons will alternatively perform a myotomy or myectomy, where a muscle is either cut or has a portion of it removed, respectively. The inferior oblique muscle is rarely tightened due to the technical difficulty of the procedure and the possibility of damage to the macula, which is responsible for central vision.
Superior oblique The superior oblique is weakened through either a tenotomy or tenectomy, where part of the muscle tendon is either cut across or removed, respectively. The superior oblique is strengthened by folding and securing the tendon to reduce its length, which is called a tuck.
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