Evidence Based Medicine: Strabismus Surgery Outcomes

Dominick M. Maino, OD,. MEd, FAAO, FCOVD-A

Professor of Pediatrics/Binocular Vision Illinois College of Optometry/Illinois Eye Institute

Lyons Family Eye Care

When you require a new hip because your old hip is giving you significant pain, your doctor often recommends physical therapy first to see if the problem can be addressed in a non-surgical manner. If the therapy does not work as well as you would like it to, a surgical consultation is then required and perhaps a surgical intervention as well. After surgery, another round of physical therapy is often conducted. This sequence of treatment (therapy, surgery, therapy) ensures you do all you can to avoid surgery if possible. If surgery is needed however, post-surgical interventions such as physical therapy ensures much better outcomes for the patient.

This does not appear to be the route many doctors recommend for those with strabismus. All too often the first suggestion is to have surgery. Seldom is it recommended to intervene with vision therapy beforehand, yet alone after surgery is completed. This sequence of events might lead you to assume that surgery is highly successful.

Evidence based medicine clearly demonstrates that this is not the case, however. In general, no matter what kind of strabismus you may have, approximately 20-30% of those undergoing surgery will require a second surgery and of these, another 20-30% may need a third surgery.

Cochrane Reviews: Various Surgical Interventions for Strabismus

For those of you not familiar with Cochrane Reviews, it is an organization trusted to review the quality of research in health care and health policy. They are internationally recognized as providing reviews of the highest standards. Their reviews assess the literature that is published on various interventions for prevention, treatment and rehabilitation. Here is what they say about surgical interventions of strabismus.

Surgical Interventions for Intermittent Exotropia. Cochrane’s reviewers tried to find randomized controlled trials (RCT) of any surgical or non-surgical treatment for intermittent exotropia. These reviewers found one RCT that was eligible for inclusion. They report that the current literature is mainly retrospective case reviews and are difficult to interpret and analyze. The one randomized trial found noted that unilateral surgery was more effective than bilateral surgery. Unfortunately, any measure of severity was lacking which meant that the criteria for intervention were poorly validated. There also appears to be no reliable natural history data as well. So does operating on one eye yield better results for exotropia? They found that surgery on one eye had an 18% fail rate while surgery on both eyes failed 48% of the time. There are many studies of surgical intervention in the literature but the methods used make it difficult to reliably interpret the results.

For Adjustable versus Non-adjustable Sutures for Strabismus interventions Cochrane notes that they did not find any studies that met the inclusion criteria for their review, however, they did look at the results of non-randomized studies that compared these techniques. The author of the review concluded that: No reliable conclusions could be reached regarding which technique (adjustable or nonadjustable sutures) produces a more accurate long-term ocular alignment following strabismus surgery or in which specific situations one technique is of greater benefit than the other. High quality RCTs are needed to obtain clinically valid results and to clarify these issues. Such trials should ideally a) recruit participants with any type of strabismus or specify the subgroup of participants to be studied … b) randomize all consenting participants to have either  adjustable or non-adjustable surgery prospectively; c) have at least six months of follow-up data; and d) include re-operation rates as a primary outcome measure.

Botulinum Toxin for the Treatment of Strabismus. Cochrane reviewers found four RCTs that were eligible for inclusion. Two of these found no difference between the use of botulinum toxin and surgery for patients requiring retreatment for acquired esotropia or infantile esotropia. There was no evidence for a prophylactic effect in an article discussing an acute onset sixth nerve palsy, and that botulinum toxin had a poorer positive outcome than surgery in patients without binocularity with horizontal strabismus. Unfortunately there was a fairly high rate of complications that included ptosis and induced vertical deviations that ranged from 24% of the population in a trial using Dysport™ to 52.17% and 55.54% in trials using Botox.™

Other Risks Associated with Strabismus Surgery

These risks include damage to structures adjacent to muscles and scleral perforations; orbital inflammations and anterior segment ischemia; slippage of muscles; lost muscles; conjunctival cysts; and various wound irregularities. Additional complications can include nausea and vomiting; serious anesthesia complications and unwanted oculo-cardiac affects. My colleague, Dr. M.K. Randhawa, using appropriate references also notes that death, surgery on the wrong eye or patient, and even blindness can occur.

Long Term Outcomes of Strabismus Surgery

A study by Awadein A,  et al stated that only 45% of children had successful outcomes at an eight-year follow up.  They also noted that 20% of the children had to undergo repeated surgeries for the strabismus which were ultimately unsuccessful as well. Another study which was conducted 10 years post-surgical intervention by Pineles et al noted that 62% achieved only a fair or poor outcome and that 60% of the patients required at least one re-operation. They also went on to state that long-term surgical results in intermittent exotropia are less encouraging when sensory status outcomes (fusion) are taken into consideration.

So do we recommend surgery as an option for our patients? Of course we do, but we use surgery as one more tool in our optometric toolbox. We use vision therapy to make sure all monocular oculo-motor, hand-eye and accommodative abilities are normalized. We then start the biocular phase of therapy to reduce or eliminate any suppression improving the sensory aspect of the visual system and then begin the binocular phase of therapy. At this point surgical intervention may be warranted to bring a large angle strabismus to a more manageable size so that we can use motor fusion and eventually sensory fusion to keep the eyes straight.

As my colleague, Dr. Len Press noted on his blog: For those not young enough to remember… there were serious schisms between orthopedic surgeons and physical therapists.  If you went to an M.D. for an opinion about an injury such as a muscle tear or broken bone, you would essentially be told you either needed surgery or you didn’t.  Doing physical therapy was a waste of time and money, and there wasn’t sufficient research to support it.  If you consulted a physical therapist you would be given advice on a non-surgical approach to rehabilitation, and be cautioned about the invasiveness and lack of predictable outcomes of surgery…..

As easily deduced from the research above, surgical intervention alone is not a panacea for strabismus and the scientific evidence is absent or lacking in many areas. We should, however, follow the example of those who came before us within the medical and therapeutic arts.

What was past is now present for optometry and ophthalmology. It is time for us to work together for the benefit of our patients. Both vision therapy and surgery has a role to play when it comes to treating strabismus. A synergy often occurs between the orthopedic surgeon and the physical therapist. We should do whatever we can to make this happen between the two eye care professions as well.

 Resources and References

A PowerPoint presentation on this topic can be found here: http://www.slideshare.net/DMAINO/strabismus-surgery-outcomes-29563247http://www.slideshare.net/DMAINO/strabismus-surgery-outcomes-29563247

Treatment for a type of childhood strabismus where one or both eyes intermittently turn outwards: available from- http://summaries.cochrane.org/CD003737/treatment-for-a-type-of-childhood-strabismus-where-one-or-both-eyes-intermittently-turn-outwards#sthash.oBUmA76b.dpuf

Adjustable Sutures: available at http://summaries.cochrane.org/CD004240/adjustable-versus-non-adjustable-sutures-for-the-eye-muscles-in-strabismus-surgery   accessed 2-14

Botulinum Toxin: available at http://summaries.cochrane.org/CD006499/botulinum-toxin-for-the-treatment-of-strabismus  accessed 2-14

Simon JW.Complications of strabismus surgery. Curr Opin Ophthalmol. 2010 Sep;21(5):361-6. doi: 10.1097/ICU.0b013e32833b7a3f.

Awadein A, Sharma M, Bazemore MG, et al. Adjustable suture Strabismus surgery in infants and children. J AAPOS 2008; 12:585–590

Pineles SLEla-Dalman NZvansky AGYu FRosenbaum AL.Long-term results of the surgical management of intermittent exotropia. J AAPOS. 2010 Aug;14(4):298-304.

Maino D. The number of placebo controlled, double blind, prospective, and randomized strabismus surgery outcome clinical trials: none!. Optom Vis Dev 2011;42(3):134-136.