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In the article titled "Is Alignment Within 8 Prism Diopters of Orthotropia a Successful Outcome for Infantile Esotropia Surgery?" by Kushner and Fisher,1 the authors' definition of the monofixation syndrome includes fusion on a distant Worth Four-Dot test display. We are not told whether the distant Worth target was presented in an illuminated black box (one common arrangement) or as an element of a visual acuity chart projection slide.
As an illuminated black box, at 20 ft the usual size of this device computes to more than the approximately 1.25 degrees of arc believed to be the limit of the central binocular field. At shorter distances, when the luxury of a long lane is unavailable, the Worth display in this form is even more clearly a peripheral binocular target. In this situation, the authors state correctly that fusors, "probably" but not definitely, had monofixation syndrome, because central fusion was
Raab EL. Is Alignment Within 8 Prism Diopters of Orthotropia a Successful Outcome for Infantile Esotropia Surgery?. Arch Ophthalmol. 1996;114(12):1530-1531. doi:10.1001/archopht.1996.01100140728021