In 2005 my colleagues and I1 described the clinical characteristics, diagnosis, and treatment of what we called the “dragged-fovea diplopia syndrome” in 83 patients, a phenomenon previously described under different names in small numbers of patients. This syndrome is characterized by central binocular diplopia in the presence of peripheral fusion. The central diplopia is caused by eccentric dragging of the fovea in 1 or both eyes by retinal disease, usually by an epiretinal membrane. Our primary contribution in that article was our description of a new test, the “lights on-off test,” which we found appeared to be pathognomonic for diagnosing the dragged-fovea diplopia syndrome. With the room lights on, a single white 20/70 letter was displayed on the black background of the visual acuity monitor. The isolated letter appeared double to patients with the dragged-fovea diplopia syndrome when viewed with both eyes open. Because peripheral fusion predominated over central fusion, and because the central foveas were misaligned with each other, there was diplopia centrally only. The room lights were then turned completely off, leaving no stimulus for peripheral fusion, and within a few seconds central fusion brought the double images of the letter together, an easily seen dynamic phenomenon confirming the presence of the dragged-fovea diplopia syndrome. Various other findings were used to establish the presence of this syndrome, such as metamorphopsia seen on the Amsler Grid test, relative comitance of the deviation on Lancaster Red-Green plotting, and the failure to obtain stable fusion with prisms. Of note, every patient with the dragged-fovea diplopia syndrome that was established by these findings responded positively to the lights on-off test, and no others responded in this way, attesting to the pathognomonic value of this test.
Guyton DL. The “Lights On-Off Test” in the Diagnosis of the Dragged-Fovea Diplopia Syndrome. JAMA Ophthalmol. Published online December 13, 2018. doi:10.1001/jamaophthalmol.2018.6048
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