[Acquired vertical diplopia in macular dystrophy as a model for obligate fixation disparity]

In patients with obligate fixation disparity central objects may be perceived as double when peripheral fusion is achieved. The diplopia cannot be resolved with prisms because the fusional power of the periphery is stronger than the central power. A different cortical integration of the peripheral and central parts of the retina is thought to be the underlying cause. We report on the clinical findings in a 45-year-old man with macular dystrophy who complained of binocular vertical diplopia of up to 1 degree. Investigation with the phase-difference haploscope revealed inhomogeneous retinal correspondence in the vertical plane, with a displacement of the visual field center relative to the periphery by 0.6 degrees. We suggest that paracentral scarring had caused displacement of receptors such that the center and the periphery could not be fused simultaneously. The case represents a model for a retinal origin of fixation disparity.