Successful treatment needs to be both cosmetic and functional
Strabismus is both a cosmetic and functional problem. It is cosmetic, as misaligned eyes make a person look different from others with normally aligned eyes. It is functional in the sense that people with strabismus do not have normal vision -their vision may be weaker than normal, they may lack depth perception and common activities like driving may be difficult.
Strabismus is treated with vision therapy or surgery or a combination of both. Strabismus can sometimes be treated with special eye-glasses. The goal of Strabismus treatment is to achieve cosmetic improvement (making the eyes look straight) and functional binocular vision (making the two eyes work together properly).
Patients need to inform themselves of the different success rates of each treatment modality as well as their complications and risks and must be mindful that an effective treatment must restore proper binocular vision (functional treatment) as well as make the eyes appear straight (cosmetic treatment).
It is important to realize that the eyes may appear straight but still not work properly (i.e. binocular vision has not been achieved). A famous example of poor binocular vision after three Strabismus surgeries is the case of Susan Barry which was chronicled in the New Yorker magazine and the book Fixing My Gaze .
Strabismus surgery cuts and reattaches the "good" eye muscle so that it balances with the "weak" muscle
Eye surgeons often speak of "relaxing" an eye muscle as the goal of Strabismus surgery. This actually involves cutting a reattaching the an eye muscle. The muscle that is cut is actually the muscle that is functioning properly, or the "good" muscle. By cutting the good muscle, the eye achieves a balance with the "weak" or improperly functioning muscle so that the eye becomes straight.
Strabismus surgery does not treat the root cause of the eye-turn. The eye turn is caused by a problem in the way that the brain communicates with the malfunctioning eye muscle. The fact that surgery does not treat the root cause is a reason why Strabismus tends to come back following surgery, often requiring repeat surgeries.
Vision therapy addresses the root cause of strabismus
Vision therapy addresses the root cause of strabismus: they problem with the eye-brain connection. That is why vision therapy, which is rehabilitative therapy for the eyes and the brain, may be a better choice to safely and effectively treat Strabismus.
The goal of vision therapy is different than that of surgery. Vision therapy treats the cause rather than the symptom. Vision therapy trains the eyes and brain to work properly so that all of the six muscles involved in eye movement are properly coordinated.
Surgery is not very good at achieving functional binocular vision
Surgery generally has relatively poor results in achieving functional binocular vision. Retrospective studies (discussed below) have shown that only 15%-22% of surgery patients achieve functional binocular vision.
Indeed, a review of the surgical literature shows that surgeons very often define success primarily in terms of cosmetic improvement only. Researcher William Ludlam notes that with surgery:
"obtaining functional binocularity as well as cosmetic alignment is so elusive that most studies of the results of strabismus surgery evaluate success solely in terms of the residual deviation [i.e. cosmetic alignment]"
Ludlam WM. The role of Surgery in the optometric management of Strabismus. Journal of Behavioral Optometry 1995. 9(4): 95-97.
Studies have looked at the success rates for Strabismus surgery
A study by Flax and Selenow in the American Journal of Optometry and Physiological Optics reviewed the literature on the Strabismus surgery going back 35 years. Only 22 published papers encompassing 1,490 patients contained pre-surgical and post-surgical comparisons using stated criteria for success. The authors found that "one third of reported cases did not achieve even the minimum benefit of being left with a low angle deviation, with the indication that one in six derived absolutely no benefit at all or were harmed by the surgery. Two thirds did achieve straight eyes, but only one-third attained normal binocular function along with alignment".
A study from 1989 examined the surgical treatment of infantile esotropia, a condition where the eye turns inwards towards the nose and is present at birth or develops at a very early age. The researchers performed a literature search going back 35 years and found 27 out of 48 studies that met the study's minimum criteria. The study found that the success rate for surgery in achieving some level of binocular vision was only 22% in 1286 patients and for achieving cosmetic improvement, the success rate was 63% in 2113 patients. Further, the need for multiple surgeries was common and there was a trend toward recurrence of the Strabismus.
A 1987 study performed a literature search going back 35 years to find articles reporting the results of the surgical management of acquired, comitant, nonaccommodative and partially accommodative esotropia. The authors found thirty-nine studies but only 15 met the minimum criteria for inclusion in the study. The success rate in achieving functional binocular vision was only 15% in 1170 patients, while the overall cosmetic success rate in making the eyes appear straight was only 43% in 1473 patients.
The authors of the later study noted that it was not possible to make direct comparisons to optometric studies because the criteria for success used in surgical studies were considerably different.
Further, it was noted that the the most prevalent complication of surgery was the need for repeated surgeries as a result of the esotropia coming back after a period of time. Most disappointing was that the data indicate that an end result of a reappearance of the esotropia was almost as likely as a functional cure.
Surgery's lack of success in achieving good binocularity and the troubling trend of repeated surgeries and recurrence of of the strabismus has predictably lead surgeons to have low expectations of the the results of strabismus surgery. In a recent journal article, one surgeon noted that "Strabismus is less a problem to be cured than a problem to be controlled, with the minimum number of surgeries": Simon, John W. Complications of Strabismus Surgery. Current Opinion in Ophthalmology. 2010. 21: 361-366.