Thursday, January 17, 2013

Vision therapy or surgery for strabismus (esotropia, exotropia)?

Strabismus surgery.  Image: wikipedia.

We here at Vision Source Vancouver think that it makes good sense to use effective non-surgical vision therapy to treat strabismus (sometimes called cross eyes, eye turn, esotropia, exotropia).  The reason is that strabismus or eye muscle surgery has many risks of bad or harmful outcomes.   

This website has featured articles outlining the risks associated with strabismus surgery and reported on studies that demonstrate the effectiveness of vision therapy in treating most kinds of strabismus -without any of the risks associated with surgery.

Professor Dominick Maino, a fellow of the College of Optometrists in Vision Development, recently had a discussion with an eye surgeon on his own blog, MainosMemos, on why surgery, because of the risks and results that are not satisfactory for many patients,  should only be used as a last resort. As only one example of undesirable outcomes, a study on surgery found that only 45% of children had successful alignment of the eyes at an eight-year follow up to their strabismus surgery. And while the low percentage was disappointing enough, 20% of the children had to undergo repeat strabismus surgeries which were ultimately unsuccessful: Awadein A, Sharma M, Bazemore MG, et al.Adjustable suture strabismus surgery in infants and children. J AAPOS 2008; 12:585–590. 

Other risks of strabismus surgery include death, infections, blindness, scars, mistakes like surgery on the wrong eye, etc.  You can read more about risks here

One can't ignore the studies regarding anesthesia and the potential for future cognitive impairment. This is a work in progress and the pediatric specialties are following closely.
However, the surgeon goes on to say:

Like anything in medicine (and you should be well-versed since you received an "Excellence in Medicine" award) you have to consider the risk-vs.-benefit ratio. If I have a young patient with a 40 PD decompensated exotropia who is in danger of developing irreversible amblyopia and loss of stereoacuity, 30-40 minutes of anesthesia for strabismus surgery is not going to prevent him or her from getting into Harvard. [NB vision therapy and patching will not touch a 40 XT]. People need to be properly educated, look at all of the facts, and not over-react.
If there are no studies that prove that anaesthesia during strabismus surgery is totally safe, our point is that it is not sensible to take the risk when you don't need to.  The basic ethical principle in medicine is "do no harm".  If there is a treatment option that has no risk of harm, it should be the first choice.  There are some types of strabismus that vision therapy cannot effectively treat, and for those surgery is probably a good idea given the cost-benefit analysis.  But for the most common kinds of strabismus, vision therapy is a safe and effective treatment. 

Dr. Maino referred to the following recent studies on strabismus surgery that highlight the reasons why it should not be first choice option for treating strabismus:

Haridas A, Sundaram V. Adjustable versus non-adjustable sutures for strabismus. Cochrane Database of Systematic Reviews 2005, Issue 1. Art. No.: CD004240. DOI: 10.1002/14651858.CD004240.pub2

"No reliable conclusions could be reached regarding which technique (adjustable or non-adjustable 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. ......"

Rowe FJ, Noonan CP. Botulinum toxin for the treatment of strabismus. Cochrane Database of Systematic Reviews 2012, Issue 2. Art. No.: CD006499. DOI: 10.1002/

The majority of published literature on the use of botulinum toxin in the treatment of strabismus consists of retrospective studies, cohort studies or case reviews. Although these provide useful descriptive information, clarification is required as to the effective use of botulinum toxin as an independent treatment modality. Four RCTs on the therapeutic use of botulinum toxin in strabismus have shown varying responses ranging from a lack of evidence for prophylactic effect of botulinum toxin in acute sixth nerve palsy, to poor response in patients with horizontal strabismus without binocular vision, to no difference in response in patients that required retreatment for acquired esotropia or infantile esotropia. It was not possible to establish dose effect information.Complication rates for use of Botox™ or Dysport™ ranged from 24% to 55.54%.

Elliott S, Shafiq A. Interventions for infantile esotropia. Cochrane Database of Systematic Reviews 2005, Issue 1. Art. No.: CD004917. DOI: 10.1002/14651858.CD004917.pub2

The main body of literature on interventions for IE are either retrospective studies or prospective cohort studies. It has not been possible through this review to resolve the controversies regarding type of surgery, non-surgical intervention and age of intervention. There is clearly a need for good quality trials to be conducted in these areas to improve the evidence base for the management of IE.

Br J Ophthalmol. 2012 Oct;96(10):1291-5. Epub 2012 Aug 11.Surgical intervention in childhood intermittent exotropia: current practice and clinical outcomes from an observational cohort study. Buck DPowell CJSloper JJTaylor RTiffin PClarke MPImproving Outcomes in Intermittent Exotropia (IOXT) Study group

After surgery 65% had fair to poor outcomes and 20% of the subjects remained XT or the XT recurred

BMC Ophthalmol. 2012 Jan 18;12:1. doi: 10.1186/1471-2415-12-1.The improving outcomes in intermittent exotropia study: outcomes at 2 years after diagnosis in an observational cohort.
Buck DPowell CJRahi JCumberland PTiffin PTaylor RSloper JDavis HDawson EClarke MP.

....8% ...of those treated surgically required second procedures for overcorrection within 6 months of the initial procedure and at 6-month follow-up 21% ... were overcorrected ....