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M. Shunmugam, M. Ugarte, M. S. Ahmad, A. Laidlaw, T. H. Williamson; Pilot Study of Metamorphopsia Quantification in Surgical Retinal Disease. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1833.
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Patients with retinal disease present with a number of definable symptoms which includes metamorphopsia. There has been considerable difficulty in designing a tool to record the nature and degree of distortion perceived by the patient. A pilot proof-of-principle study was performed to validate a new method of quantifying the nature & degree of metamorphopsia using modified Amsler charts.
Patients with unilateral epiretinal membranes (ERM) and full-thickness macular holes were prospectively recruited and presented with modified Amsler charts with gradations of increasing line thicknesses. The line thickness at which their distortion failed to be manifest was recorded. Patients were then asked to match the patterns of distortion they noted with modified Amsler grids of 10 differing sinusoidal distortion patterns and corresponding grid displacements/excursions of between 1% to 8% (in single percentage increments). These results were compared with LogMAR visual acuity, contrast sensitivity, stereopsis, subjective Amsler grid assessment, dominance & optical coherence tomography (OCT) characteristics.
Twenty-five patients with a mean age of 70 yrs (SD = 7.7) identified pattern distortion displacement which statistically correlated with near & distance visual acuity (p < 0.01), contrast sensitivity (p < 0.01) & ERM central foveal thickness on OCT scanning (p < 0.01) . The line thickness threshold at which distortion was noted correlated with visual acuity (p < 0.01), stereopsis (p = 0.01) & the number of Amsler grid squares affected (p < 0.02). The actual pattern of grid distortion however did not correspond to any clinical indices.
Subjective symptoms of metamorphopsia can be quantified and this test may provide a quick office-based tool to monitor the severity of certain retinal conditions. The degree of image displacement is more clinically relevant than actual distortion pattern perception.
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