Strabismus - a condition where the eye abnormally turns in or out due to one or more of the eye muscles malfunctioning - is often treated with surgery in which the properly functioning muscle is cut and re-attached so that it balances with the malfunctioning muscle, hopefully making the eyes look straight.
Strabismus surgery has well many well-known risks and complications. However, there is a growing body of research that is causing even more worry for strabismus surgery patients because these patients are often very young and must frequently endure repeat surgeries, which means repeat exposure to anesthesia and therin lies the risk.
Recent research suggests that the risk of developing learning disabilities and attention-deficit/hyperactivity disorder (ADHD)increases after early exposure to surgeries requiring general anesthesia - surgeries like strabismus surgery.
Repeat strabismus surgeries are common
Eye surgeons often lament the need for repeat eye surgeries for strabismus patients. Surgeon, John W. Simon, notes that "patients must regularly contend with the unfortunate reality that even the most accurately planned and carefully executed surgery may not totally eliminate the deviation [i.e. the misalignment of the eyes] or completely normalize rotations. In addition, strabismus tends to recur over time." This limitation of sugery often results in the the patient being subjected to repeated surgeries - all of which may be unsuccessful. It is not uncommon for a patient to have had two or three or more surgeries and still have a noticeable misalignment or poor binocular vision together with depth perception problems or all three. For this reason, the surgeon's view is 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.
One study 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.
Recent studies link repeat exposure to anesthesia at an early age to learning disabilities and ADHD
The latest study to link repeated anesthesia exposure to learning/behavioral disorders was published by researchers at the Mayo Clinic in February, 2012 in Mayo Clinic Proceedings. It linked repeat surgeries requiring anesthesia to a doubling of the risk of developing ADHD. The study's authors concluded that "children repeatedly exposed to procedures requiring general anesthesia before age 2 years are at increased risk for the later development of ADHD even after adjusting for comorbidities."
The February 2012 study follows up on earlier studies that linked repeat surgeries requiring anesthesia to an increased risk of developing learning disabilities. The authors of an October 2011 study on anesthesia and learning disabilities published in the journal Pediatrics stated the alarming conclusion that "[r]epeated exposure to anesthesia and surgery before the age of 2 was a significant independent risk factor for the later development of [learning disabilities] but not the need for educational interventions related to emotion/behavior. We cannot exclude the possibility that multiple exposures to anesthesia/surgery at an early age may adversely affect human neurodevelopment with lasting consequence."
Similar results were published in a 2009 study published in the journal Anesthesiology which looked at children under the age of 4 who were exposed to anesthesia. The researchers concluded that “exposure to anesthesia was a significant risk factor for the later development of learning disabilities in children receiving multiple, but not single anesthetics. These data cannot reveal whether anesthesia itself may contribute to learning disabilities or whether the need for anesthesia is a marker for other unidentified factors that contribute to learning disabilities."
The three studies referenced above were undertaken after studies in animals showed that repeat exposure to anesthesia at a young age caused damage and degeneration in the brain that manifested in the animals as learning and behavioral problems. The research conducted so far in humans indicates that the worrisome findings from the animal studies apply to humans as well.
UPDATE: new study shows that even a single exposure to anesthesia during surgery is associated with developmental problems in children. [updated January 18, 2013]
There is now new evidence that even a single exposure to anesthesia can be dangerous for a child. A study published in December 2012 in the journal Evidence Based Medicine found that children exposed to anaesthesia for surgery under 3 years of age were found to be at significantly increased risk for developing disabilities in receptive language, expressive language, total language and abstract reasoning at age 10.
The study authors commented that:
This study was the first to report the effects of anaesthetic exposure early in life on neuropsychological outcome using individually administered neurocognitive tests. Perhaps due to the greater sensitivity of these tests, Ing and colleagues observed disability even following a single exposure in early childhood, while several previous reports, utilising group-administered tests, had only detected learning abnormalities following multiple exposures.
Is general anesthetic used for young patients undergoing strabismus surgery?
While topical and local anesthesia are used for some strabismus surgeries in certain patient demographics, it appears that general anesthetic is commonly used for children younger than the mid-teens. Click here to read more about anesthesia use in strabismus surgery. According to Cyber-Sight, a program of ORBIS International, a non-profit organization that prevents and treats blindness by providing quality eye care, "most immature patients (younger than midteens) require general anesthesia for extraocular muscle surgery."
Because doing strabismus surgery early in life is generally considered important to its success, surgery in children younger than age 2 is not unusual. Surgery for strabismus is done as early as 3 months of age in serious cases, particularly if the strabismus is detected early.
Given the potential for very bad outcomes following repeat surgeries and the high risk of repeat surgery for strabismus, it is prudent to employ non-surgical treatments where they are available. Vision therapy is an effective non-surgical treatment for most kinds of strabismus. The success rate of vision therapy treatment of strabismus is in the range of 75%-87%.
Unfortunately, some forms of strabismus do not respond well to vision therapy and surgery may be required. If surgery is necessary to treat a young patient, surgical approaches that do not rely on general anesthesia, if they are available, should be considered.
While the studies referenced above looked at very young children, at what age does the risk of of learning and behavioral disorders diminish and at what age does it disappear? Does the risk ever disappear? We don't know the answer yet but we know that the brain continues to develop until the age of about 25. What is the risk of damage during the full 25 years of brain development?
Ask your doctor the right questions
Patients contemplating strabismus surgery should have a frank discussion with their doctor and raise the issue of repeat surgeries and the risk of learning disabilities and ADHD that comes with repeat exposure to anesthesia.
Also note that strabismus surgery has other complications and risks in addition to the risk posed by repeat exposure to anesthesia.