Minimal Angle Horizontal Strabismus Detectable by Lay Observers

Purpose. Patients with socially significant strabismus may be at risk for certain psychosocial consequences. However, the magnitude at which strabismus becomes socially significant is ill defined. Suggested criteria for socially significant strabismus can be found in the literature, but they are rarely, if ever, referenced. The purpose of this study is to further define the magnitude at which strabismus becomes socially significant according to lay observers. Methods. Strabismus was simulated using photo manipulation and off-center fixation. Horizontal deviations were created in 3Δ steps up to 24Δ. One model was used for all photos. The photos were presented in random order to non-health care professionals (N = 58). Participants were instructed to view each picture and determine: “yes, this person has an eye turn” or “no, this person does not have an eye turn.” A χ2 test was used for analysis. Results. There was an increase in the likelihood of strabismus detection as the size of the angle increased for exotropia and esotropia. Overall, exotropia was easier to identify than esotropia. For esotropia, a dramatic increase in detectability occurred between 9Δ (47.41% detection; p = 0.001) and 12Δ (67.24% detection; p = 0.001), with 70% detection being achieved at 14.5Δ. A significant increase in detection of exotropia occurred between 6Δ (60.34% detection; p = 0.001) and 9Δ (77.59% detection; p = 0.001), with 70% detection achieved at 8Δ. Conclusions. Our results suggest that exotropia is easier for lay observers to detect than esotropia, with the critical magnitude (70% detection) being 14.5Δ for esotropia and 8Δ for exotropia. This refutes generally accepted beliefs that esotropia is easier to detect than exotropia. Additional studies are needed to look at the effect of ethnicity, sex, and age. Multiple models should be used to reduce the possible influence of distinct facial characteristics and increase the generalizability of the results.