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K. Kroyer, U. Christensen, M. la Cour, M. Larsen; Measuring Metamorphopsia in Patients with a Unilateral Stage 2 or Stage 3 Macular Hole in the COMAH Study . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3711.
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© ARVO (1962-2015); The Authors (2016-present)
Photoreceptor displacement during the development of a macular hole changes the spatial projection of the affected photoreceptors, inducing a sensation of micropsia within the affected part of the visual field. We have developed a new method for measuring basic aniseikonia in patients with a unilateral macular hole and used it to examine photoreceptor displacement in patients with a macular hole.
Our basic aniseikonia test requires the patient to assess the relative size of two dichoptically presented half–discs which when seen in combination by a healthy subject compose a perfectly round disk, vertically divided into two halves of equal size but different color. When the patient sees two paired stimuli as being of unequal size, the stimulus for the diseased eyed is increased in size in small increments until perceived as being of the same size as the reference stimulus shown to the healthy eye. The disparity in true size is a measure of angular photoreceptor displacement or aniseikonia. The test is conducted for a range of stimulus diameters, comprising 110 pairs of semicircular disks ranging in size from 1 to 15 degrees, with increments of 0.5 degrees and differences within pairs of stimuli between 0 and 1.5 degrees presented in random order. The test result is displayed as a disparity map rendering retinal disparity as a function of eccentricity. The study included 20 patients with a unilateral stage 2 or stage 3 macular hole and a reference population of 10 healthy subjects with normal binocular vision.
In the 20 patients with a unilateral stage 2 or stage 3 macular hole, interocular perceived size disparity ranged from zero to 1.5 degrees of visual angle. Patients with a macular hole demonstrated a central scotoma ranging from 0 to 2.5 degrees visual angle. In the 10 healthy subjects disparity between the two eyes did not reach the detection threshold of 0.5 degrees.
Retinal disparity associated with a macular hole can be mapped as a function of visual field eccentricity using a simple stimulus designed specifically to suit the visual distortion induced by the macular hole. This study confirms previous work demonstrating radial centrifugal photoreceptor displacement away from the center of the retina in eyes with a macular hole. Future studies will test if this newly developed disparity test can be used to predict the anatomical and functional outcome of vitrectomy for macular hole.
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