Strabismus is an inability of one eye to attain binocular vision with the other because of imbalances of muscles of the eyeball. The goals of strabismus surgery are to obtain normal visual acuity in each eye, to obtain or improve fusion, to eliminate any associated sensory adaptations or diplopia, and to improve visual fields.

In adults, the sudden onset of strabismus usually follows head trauma, intra-cranial hemorrhage, or brain tumor. Adults with new-onset strabismus develop diplopia. Correction of strabismus should result in binocular vision and fusion of images. Adults with congenital strabismus, however, usually have failure of visual development (amblyopia) in the deviating eye; correction of ocular mis-alignment is unlikely to achieve stereopsis and fusion.

Surgery for correction of strabismus consists of weakening or strengthening the extra-ocular muscles. For correction of exotropia, the lateral rectus muscle is weakened by recession. The muscle is detached at its insertion and then re-sewn posteriorly to the sclera at a distance not to exceed 8 mm from the original insertion while the medial rectus is cut at its insertion and a part of the muscle not to exceed 6 mm is resected. The muscle is sutured to its original insertion. The amount of recession and resection and the number of extra-ocular muscles resected or recessed are determined by the degree of ocular deviation (squint). In patients with esotropia, the medial rectus is recessed and the lateral rectus is resected. For vertical deviation, the vertical muscles are recessed, resected, tucked, or weakened by disinsertion (e.g., inferior oblique muscles).

Use of Amniotic Membrane in Strabismus Surgery

In a prospective, randomized study, Kirsch et al (2014) evaluated the effect of amniotic membrane in reducing inflammation, fibrosis, adhesion formation, and ocular motility restrictions following strabismus surgery. In the first stage, a total of 17 rabbits underwent superior rectus muscle recession in both eyes. Surgery was performed in the same manner, but human amniotic membrane was placed over the muscle without sutures in the right eye after recession. After 15 days, the rabbits were killed and their orbits were exenterated and evaluated histopathologically to quantify tissue inflammation and fibrosis. In the second stage, 5 rabbits underwent the same procedure but were killed after 30 days. A dynamometer was used to measure the force required to displace all eyes. At 15 days post-operatively, eyes with amniotic membrane exhibited an increased inflammatory response and less fibrosis than eyes without amniotic membrane. At 30 days post-operatively, eyes with amniotic membrane continued to exhibit increased inflammation and less fibrosis than eyes without amniotic membrane. In the dynamometer test, more force was needed to displace eyes without amniotic membrane after 15 days, but there was no significant difference between the forces needed at 30 days. The authors concluded that human amniotic membrane in rabbits led to an increase in the inflammatory process and a decrease in fibrosis formation following strabismus surgery.

Kennedy and colleagues (2018) evaluated wound tensile strength as well as histopathologic changes following strabismus surgery with amniotic membrane grafts (AMGs) in 20 New Zealand white rabbits. All subjects underwent 4-mm inferior rectus hang-back recessions to both eyes. The right eyes served as controls; 10 left eyes (group 1) received processed dehydrated amniotic membrane allografts (Ambiodry2, IOP Inc., Costa Mesa, CA) and 10 left eyes (group 2) received cryo-preserved human amniotic membrane allografts (AmnioGraft, Bio-Tissue, Miami, FL) between the sclera and muscle insertion and between the muscle and re-positioned conjunctiva. At post-operative month 1, tensile strengths of the muscle-globe and conjunctiva-globe attachments were measured, and histopathologic analysis of each eye was performed. In group 1, the mean tensile strength of the muscle-globe attachments was 441.4 ± 274.4 g; of the conjunctiva-globe attachments, 640.3 ± 266.4 g. In the control eyes, the comparable values were 365.8 ± 199.8 g and 595.2 ± 315.3 g, respectively (p = 0.19, p = 0.13). In group 2 the mean tensile strengths were 456 ± 297.5 g and 608.2 ± 306.7 g, compared with control values of 352.7 ± 114.8 g and 583.8 ± 347.1 g (p = 0.43, p = 0.45). The authors concluded that there was no significant change in tensile strength of the muscle insertion using AMGs. They stated that in a rabbit model, AMGs did not reduce inflammation or improve scar formation 1 month after strabismus surgery.

Kassem and El-Mofty (2019) noted that adhesions between the extra-ocular muscles and surrounding tissues pose a main cause of failure of strabismus re-operations. Amniotic membrane transplantation during extra-ocular muscle surgery, to prevent the formation of adhesions, has been a subject of research during the past 10 years. These investigators examined the value, indications, and tips on usage of AM transplantation during strabismus surgery. All references cited in PubMed in English were searched using the key words: amniotic membrane strabismus or amniotic membrane extraocular muscles, and a brief summary of these was described. In addition, certain articles were chosen to provide introductory information on wound healing and fibrosis, AM properties and how it works following transplantation, and AM processing and preservation. Amniotic membrane used for transplantation during extra-ocular muscle surgery may be cryo-preserved, dried, or fresh. It may be oriented with its stroma or epithelium towards the muscle. It may or may not be fixed with sutures. What were the best choices? Various studies attempted to answer these questions. Many of the studies reviewed, however, were inconclusive or contradictory. Fresh AM appeared effective, but carried a risk of transmission of communicable diseases. Dried membrane was not of value in preventing adhesions. Histopathologically, cryo-preserved membrane prevented the development of adhesions in the region of its presence, regardless of its orientation, and without the need for suture fixation. To accentuate this histopathological effect during clinical practice, it was recommended to utilize the largest segment possible of cryo-preserved membrane and limit its usage to cases where adhesions are expected to be the main cause of failure of strabismus surgery. The authors concluded that cryo-preserved AM transplantation was safe and histopathologically effective in preventing adhesions. However, this effect was less pronounced clinically. These researchers stated that the use AM during strabismus re-operations is merited if previous recommendations and precautions are considered.

Surgical Adhesives

Guhan and colleagues (2018) noted that tissue adhesives are gaining popularity in ophthalmology, as they could potentially reduce the complications associated with current surgical methods. An ideal tissue adhesive should have superior tensile strength, be non-toxic and anti-inflammatory, improve efficiency and be cost-effective. Both synthetic and biological glues are available. The primary synthetic glues include cyanoacrylate and the recently introduced polyethylene glycol (PEG) derivatives, while most biological glues are composed of fibrin. Cyanoacrylate has a high tensile strength, but rapidly polymerizes upon contact with any fluid and has been associated with histotoxicity. Fibrin induces less toxic and inflammatory reactions, and its polymerization time can be controlled. Tensile strength studies have shown that fibrin is not as strong as cyanoacrylate. While more research is needed, PEG variants currently appear to have the most promise. These glues are non-toxic, strong and time-effective. Through Medline and internet searches, the authors presented a systematic review of the current applications of surgical adhesives to corneal, glaucoma, retinal, cataract and strabismus surgeries. They concluded that this review suggested that the use of surgical adhesives is a promising approach to reduce problems in current ophthalmic surgical procedures.

Collagen Matrix Implant for Reduction of Adhesions in Restrictive Strabismus

In a prospective, masked-observer, controlled experimental study, Yoo and colleagues (2019) examined the efficacy of a biodegradable collagen matrix implant (Ologen, Aeon Astron Europe BV, Leiden, the Netherlands) in reducing adhesions in a rabbit model of restrictive strabismus. A total of 60 superior rectus muscles of 30 rabbits were resected and Marlex mesh was fixed beneath the resected muscle using non-absorbable suture; 40 eyes underwent one of two different procedures; the resected muscle was wrapped with preserved human AM (AM group) or Ologen (Ologen group). Randomly selected 20 eyes served as controls. Eyes were enucleated at 4 weeks after surgery to measure the severity of adhesion using a push-pull gauge; histopathological examination was performed. At post-operative week 4, the average tensile strength of the myo-scleral adhesion was significantly lower in the Ologen group (151.8 ± 42.7 gram force) compared to controls (347.9 ± 68.6 gram force) and AM group (193.0 ± 44.3 gram force) (p < 0.001 and p = 0.045, respectively). Ologen group showed significantly lower degree of acute inflammation, chronic inflammation and rectus muscle fibrosis compared with controls (all p < 0.01). The degree of chronic inflammation was significantly lower in the Ologen group compared with AM group (p = 0.012). The authors concluded that compared to AM, Ologen was more effective in reducing mesh-related extra-ocular muscle adhesions in a rabbit model of restrictive strabismus.

Scope of Policy

This Clinical Policy Bulletin addresses strabismus repair .

Medical Necessity

Aetna considers strabismus repair medically necessary for adults 18 years of age or older only if both of the following criteria are met:

Strabismus surgery is considered medically necessary for children diagnosed with strabismus.

Experimental and Investigational

Cosmetic