Example of the result of vertical (VM = 0.4°) (left) and horizontal (HM = 0.5°) (right) M-chart. Dotted lines are shown to the subject one after another (starting with the solid line - 0°), until the subject recognizes the line as being straight. In this case the vertical solid line was very distorted, following lines with larger dot intervals were recognized as less distorted. Line 0.4° was recognized as straight, thus the vertical metamorphopsia score is 0.4°. After rotating M-charts 90° into the horizontal direction the same procedure was perfomed, until line 0.5° was recognized as straight, thus the horizontal M-chart score is 0.5°.