Strabismus surgery (also: extraocular muscle surgery, eye muscle surgery, or eye alignment surgery) is surgery on the extraocular muscles to correct strabismus, the misalignment of the eyes. With approximately 1.2 million procedures each year, extraocular muscle surgery is the third most common eye surgery in the United States. 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.
Isolating the inferior rectus muscle
- Eye muscle surgeries typically correct strabismus and include the following:
- Loosening / weakening procedures
- Recession involves moving the insertion of a muscle posteriorly towards its origin.
- Tightening / strengthening procedures
- Transposition / repositioning procedures
- Adjustable suture surgery is a method of reattaching an extraocular muscle by means of a stitch that can be shortened or lengthened within the first post-operative day, to obtain better ocular alignment.
- Loosening / weakening procedures
Strabismus surgery is a one-day procedure. The patient spends only a few hours in the hospital with minimal preoperative preparation. The average duration of the surgery is variable. After surgery, the patient should expect soreness and redness. In cases of re-operations, more pain is expected. Resection of the muscles is more painful in the post operative period than recession. It also leaves redness that lasts longer and may cause some vomiting in the early post operative period.
The surgeon will provide the patient with a cover for his or her eyes that prevents light from entering. It is advisable for the patient to wear this, since stimulus to the eye (e.g., light, rolling of eyes) will cause discomfort.
Alignment and functional changes
Over- and undercorrection: Surgical intervention can result in the eyes being entirely aligned (orthophoria) or nearly so, or it can result in an over- or undercorrection that may necessitate further treatment or another surgical intervention. The likelihood that the eyes will stay aligned over the longer term is higher if the patient is able to achieve some degree of binocular fusion after surgery than if not. In a study on infantile esotropia patients who had either small-angle (8 diopters) esotropia or small-angle exotropia of the same size six months after the intervention, it was found that those who had the small-angle esotropia were more likely to have aligned eyes five years after the intervention than those with small-angle exotropia. There is tentative evidence that children with infantile esotropia patients achieve better binocular vision post-operatively if the surgical treatment is performed early (see: Infantile esotropia#Surgery).
Other deviations: Strabismus surgery for oblique muscle disorders may result in consecutive misalignment of the eyes. First of all, dissociated vertical deviation may occur. There are indications that the severity of this deviation may be lower if a child is operated at a very young age. Secondly, strabismus surgery may also result in subjective and objective cyclodeviation, possibly resulting in cyclotropia and rotational double vision (cyclodiplopia) if the visual system cannot compensate for it.
For pure horizontal rectus muscle surgeries, it is known that vertical deviations, A and V patterns and cyclotropia can be anticipated or avoided by taking certain surgical precautions.
Functional considerations: A frequent outcome of strabismus surgery is consecutive microtropia (also known as monofixation syndrome).
Functional improvements and further benefits: For a long time it was thought that adult patients with long-standing strabismus could achieve only cosmetic improvement; in recent years there have been cases in which sensory fusion has occurred also in this type of patients provided that postoperative motor alignment is very high. In case of pre-operative inward squint the correction expands the binocular visual field of the patient, improving peripheral vision. Furthermore, the restoration of ocular alignment can bring about psychosocial and economic benefits to the patient (see also: Psychosocial effects of strabismus).
Diplopia occurs rather frequently in the first few weeks following surgery.
Complications that occur rarely or very rarely following surgery include: eye infection, hemorrhage in case of scleral perforation, muscle slip or detachment, or even loss of vision.
Eye muscle surgery gives rises to scarring (fibrosis); if scarring is extensive, it may be seen as raised and red tissue on the white of the eye. Fibrosis can be reduced by use of mitomycin C during surgery.
A relatively new method, primarily devised by Swiss ophthalmologist Daniel Mojon, is minimally invasive strabismus surgery (MISS)which has the potential to reduce the risk of complications and lead to faster visual rehabilitation and wound healing. Done under the operating microscope, the incisions into the conjunctiva are much smaller than in conventional strabismus surgery. A study published in 2017 documented fewer conjunctival and eyelid swelling complications in the immediate postoperative period after MISS with long-term results being similar between both groups. MISS can be used to perform all types of strabismus surgery, namely rectus muscle recessions, resections, transpositions, and plications even in the presence of limited motility.
Very rarely, potentially life-threatening complications may occur during strabismus surgery due to the oculocardiac reflex.
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