M-charts as a tool for quantifying metamorphopsia in age-related macular degeneration treated with the bevacizumab injections

Abstract

Background: This article is aimed to assess quantitatively metamorphopsia using M-charts in patients suffering from wet age-related macular degeneration (AMD) treated with the intravitreal bevacizumab injections and to compare the results with traditional Amsler grid and ocular coherence tomography (OCT).

Methods: Thirty-six patients diagnosed with wet AMD were examined one day before and one month after the intraocular injection of bevacizumab. Horizontal and vertical metamorphopsia scores using M-charts, distance visual acuity, Amsler test and OCT were performed at each visit. Additionally, 23 healthy subjects were examined as a control group.

Results: The rate of metamorphopsia detection was 89% with M-charts and 69% with Amsler test. The horizontal metamorphopsia score improved in 22 patients, the vertical metamorphopsia score improved in 16 patients, the Amsler grid results improved in 6 patients, visual acuity improved in 17 patients. There was no correlation between the degree of metamorphopsia and the visual acuity or the central retinal thickness (CRT). The specificity of both the M-charts and Amsler grid was 100%.

Conclusions: The rate of metamorphopsia detection in wet AMD patients was better with M-charts than with Amsler grid. M-charts may be used in the assessment of efficacy of treatment with intravitreal bevacizumab injections as another outcome measure, moreover they can be used even at home for the self-assessment. M-charts provide additional information concerning the visual function, independent of the visual acuity, CRT and morphological changes in OCT.

Figure 1

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°.

Figure 2

Medians of the vertical - VM (left) and horizontal - HM (right) metamorphopsia score obtained with M-charts before and after the bevacizumab injection.