Quantification of changes in metamorphopsia and retinal contraction in eyes with spontaneous separation of idiopathic epiretinal membrane

Abstract

Background: To quantify changes in metamorphopsia and retinal contraction in eyes with idiopathic epiretinal membrane (ERM) before and after a spontaneous separation of ERM.

Methods: Among 92 eyes of 92 patients with idiopathic ERM who were followed up at our hospital, 5 eyes of 5 patients had experienced a spontaneous separation of ERM during the follow-up period. Patient's metamorphopsia was assessed horizontally and vertically by a metamorphopsia chart developed by our group, M-CHARTS, to obtain the horizontal (MH) and vertical (MV) metamorphopsia scores. Difference in the scores before and after the membrane separation represents change in patient's metamorphopsia. Changes in retinal contraction were also evaluated horizontally and vertically with our original software for fundus image analysis. The difference between M-CHARTS scores and distances of retinal vessel movements with before and after membrane separation were measured.

Results: All five subjects showed a decrease in the retinal contraction. Improved visual acuity was observed in three subjects, and no change was seen in the other two. Four subjects obtained better metamorphopsia scores after the membrane separation, while the other one was not detected with metamorphopsia by M-CHARTS either before or after the separation. In subjects with an improved MV, horizontal retinal movement was seen larger than the vertical movement. Similarly, the subjects with an improved MH indicated a larger vertical retinal movement than the horizontal movement.

Conclusions: The direction of patient's metamorphopsia closely associated with the direction of retinal contraction before and after a spontaneous separation of ERM.

Figure 1

(a) Method of detecting metamorphopsia using M-CHARTS. The minimum visual angle of the dotted lines needed to cause the metamorphopsia to disappear was measured. (Quantification of retinal contraction using fundus photograph.) (b) The comparison image (after-: after spontaneous separation of ERM) was superimposed on the baseline image (before-: before spontaneous separation of ERM) so that the optic disc and choroidal vessels matched. The distance between the center of the optic disc and fovea was calibrated to be 15° (4.02 mm), and 20° macula area was divided into 25 areas. In each of the 25 areas, two overlapping fundus images were flickered back and forth at a speed of 2 Hz, and the retinal vessels were exactly matched manually. (c) The movement of retinal vessels in each of the 25 areas was a displayed as a vector and the value of each vector's vertical and horizontal components was recorded in millimeters (mm) as the index of retinal contraction. For easier visibility, the vector arrows are shown three times larger than the actual measured vectors.

Figure 2

SLO images obtained with an argon blue laser beam and results of Amsler charts and M-CHARTS in patient no. 1. (a) Before-, (b) 41 months later from first visit to our hospital and (c) after- SLO images. (d) The results of M-CHARTS evaluations of metamorphopsia at before, 41 months later and after spontaneous separation of ERM. (e) The results of Amsler charts evaluations of metamorphopsia at before and after spontaneous separation of ERM. (f) The fundus image with vector arrows, which was analyzed by our developing software, shows the direction and distance of retinal vessel movements.

Figure 3

SLO images obtained with an argon blue laser beam and results of Amsler charts and M-CHARTS in patient no. 3. (a) Before- and (b) after- SLO images. (c) The results of Amsler charts and M-CHARTS evaluations of metamorphopsia at before and after spontaneous separation of ERM. (d) The fundus image with vector arrows, which was analyzed by our developing software, shows the direction and distance of retinal vessel movements.

Figure 4

SLO images obtained with an argon blue laser beam and results of Amsler charts and M-CHARTS in patient no. 5. (a) Before- and (b) after- SLO images. (c) The results of Amsler charts and M-CHARTS evaluations of metamorphopsia at before and after spontaneous separation of ERM. (d) The fundus image with vector arrows, which was analyzed by our developing software, shows the direction and distance of retinal vessel movements.