Questionnaire for Strabismus Post Surgery Expectations The British Journal of Ophthalmology August 06, 2015
Published in Eye Care, Written by Bruce Bridgeman PhD
Strabismus Surgery and Stereopsis
This study by McBain and colleagues adds valuable new data and analysis while documenting limitations of strabismus surgery which have bedeviled the field for a long time. According to the article, most patients understandably expect improvement in their condition after surgery, yet only one-quarter are successfully realigned by standard clinical criteria. A result is repeated surgeries. Perhaps for many patients the problem is more in their brains than in their extraocular muscles. In 1868, Ewald Hering in his book introducing his law of equal innervation used the analogy of controlling two horses with a single set of reins.1 Strabismus surgery is analogous to correcting a horse’s deviated gait by shortening one of his reins. Before long the horse deviates again, because the problem is in the horse and not in the reins. A similar phenomenon occurs in prism correction, where some patients are observed to “eat” the correction and deviate again. The brain has a mistaken idea of where the eye or the correspondence of images should be, and resists efforts to correct it. Unfortunately we are not yet in a position to correct the brain’s gaze controller.
Conspicuously absent in the study is evaluation of deficits in stereopsis, which are common in strabismus. It has recently become clear that stereo can be acquired in adulthood, far beyond the traditional critical period in childhood.2,3 By introducing a large sample of strabismus surgery patients, the article invites a comparison with a survey that Sue Barry and I, with Leonard Press’s cooperation, have initiated for people who have acquired stereopsis as adults. Athough the survey is incomplete (responses are still coming in at http://bit.ly/1vThYaM), small (51 responses so far), and non-random, it can already give a rough idea of differences between a strabismic population, presumably with accompanying stereopsis deficits, and a population who has acquired stereo as adults. The sex ratio of the two groups is nearly identical, with slightly more females than males (52% in our survey vs 54% in the surgery population). Yet there is a large difference in initial deviations; only 27% in our misaligned sample are exotropic, while the surgery population has a majority of exotropes (80 exotropic vs 63 esotropic). All but 4 of our sample had been stereo-deficient as long as they could remember, while the average age of onset for the surgery population was 21 years.
Although our survey is incomplete and analysis is just beginning, these differences begin to point to characteristics of a population who might be candidates for acquisition of stereopsis as adults. Our hope is that in the future stereo deficiency will be seen as a curable condition for many strabismic or otherwise stereo-deficient adults.
References
- Hering E. Die Lehre vom Binokularen Sehen. 1868. Translated as: The Theory of Binocular Vision. Bridgeman B, Translator. Bridgeman B, Stark L, eds. New York, NY: Plenum Press; 1977.
- Barry SR. Fixing My Gaze: A Scientist’s Journey into Seeing in Three Dimensions. New York, NY: Basic Books; 2009.
- Bridgeman B. Restoring adult stereopsis: A vision researcher’s personal experience. Optom Vis Sci. 2014;91(6):135-139. http://journals.lww.com/optvissci/pages/articleviewer.aspx?year=2014&issue=06000&article=00017&type=abstract