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David Yorston, Velichko Manahilov, Gerard F McGowan, Naill Strang; Mapping metamorphopsia in macular hole and epiretinal membrane. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4537.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a test to quantify metamorphopsia within the central visual field in patients with macular disease.
The test uses octagonal grids, divided into eight segments, formed by black elements (squares) of various densities. These charts contain grids at varying eccentricities between 0.5 and 12 degrees from fixation. Patients were instructed to look at the fixation disk in the centre of the D-charts and report if the grid appeared distorted by indicating with their finger which 45 degree sectors appeared distorted. The metamorphopsia score (the maximal element separation which produced perception of distortion) was determined for each ring and sector. The results provide a two dimensional map of metamorphopsia severity (see Figure). 33 patients (mean age 70.8; SD 7.1 years) with epiretinal membrane (ERM) and 41 patients (mean age 71.5; SD 6.4 years) with macular hole (MH) were tested before surgery. 15 patients (9ERM and 6MH) were also tested following surgery.
Mean LogMAR visual acuity (VA) for ERM was 0.53 (SD 0.25) and for MH it was 0.95 (SD 0.29). Metamorphopsia was detected in the three central rings from 0.5-7 degrees from fixation, but rarely in the 7-12 degree outer ring. The total metamorphopsia score (Mtotal) showed a skew distribution, with median scores of 7.2 degrees for ERM and 10.2 degrees for MH which were not significantly different (Mann-Whitney, p=0.22). The median metamorphopsia area (Marea) scores for ERM patients (21.9%) and MH patients (37.5%) did not differ significantly (Mann-Whitney, p=0.23). Mtotal was closely correlated with the Marea (Spearman rank correlation=0.97, p<0.001) but not with VA . Following surgery patients showed a significant reduction in Mtotal (Mann-Whitney, p=0.0016),and an increase in VA (p=0.02) but there was no correlation between the changes in VA and Mtotal.
D-Charts enable metamorphopsia to be quantified and localised in ERM and MH patients with a wide range of visual acuities. The Mtotal score gives a single continuous variable for measuring metamorphopsia, which is not related to VA. The results demonstrate that the D chart is an effective tool to map changes in metamorphopsia pre- and post-surgery, and may be useful in selecting which patients will benefit from an operation.
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