Changes in retinal vascular geometry after vitrectomy in idiopathic and uveitic epiretinal membrane

Abstract

Epiretinal membrane (ERM) can arise idiopathically or secondary to uveitis, each driven by distinct pathophysiological mechanisms. Because ERMs exert tractional forces that distort both the retina and its vasculature, vascular geometry can serve as an indirect marker of the tractional forces acting on the retina. This study aimed to evaluate the associations between postoperative changes in retinal vascular geometry and functional outcomes in patients with idiopathic and uveitic epiretinal membrane (iERM and uERM). A retrospective analysis was performed on 72 eyes (42 iERM, 30 uERM) that underwent pars plana vitrectomy for ERM. Retinal vascular geometric parameters, including arterial and venous angles, branching angles, and tortuosity, were quantitatively measured using conventional retinal fundus photographs. Best-corrected visual acuity (BCVA) and central foveal thickness (CFT) were measured preoperatively and at 1 and 6 months postoperatively. The primary outcome was the comparison of postoperative changes in retinal vascular geometry between iERM and uERM, while the secondary outcome assessed improvements in BCVA, M-score, and CFT, and their correlation with vascular changes. Greater postoperative changes in arterial angle were significantly associated with improvements in BCVA and CFT. The iERM group exhibited more pronounced changes in retinal vascular geometry than the uERM group, particularly in branching venous angles and venous tortuosity. These differences became more evident over time. In conclusion, this study demonstrates that postoperative changes in retinal vascular geometry differ between patients with iERM and uERM, with more significant changes observed in iERM. These findings provide valuable insight into the distinct recovery mechanisms in iERM and uERM, emphasizing the roles of tractional forces and inflammation in shaping postoperative outcomes.

Keywords: Arterial angle; Epiretinal membrane; Fundus photo; Tortuosity; Uveitis; Venous angle.

Fig. 1

Evaluation of retinal vascular geometry. All measurements were performed using ImageJ. (A) The distance between the optic nerve head (ONH) and the fovea was measured, and a circle (black dotted circle) was drawn with a radius equal to this distance, centered on the ONH. The intersection points where the circle crossed the arteries and veins of the superior and inferior arcade vessels were identified. Angles between these intersection points and the ONH (marked as a and b) were calculated. The bifurcation angles of retinal arteries and veins (c and d) were measured at the first bifurcation within the major arcade. (B) Retinal arterial and venous tortuosity were calculated as the ratio of the actual vessel length along the vessel path (red and blue dotted lines) between the first and second bifurcation points to the straight-line distance (red and blue solid lines) between the same points. Tortuosity values are expressed as a/a’ and b/b’.

Fig. 2

Representative cases from the idiopathic (iERM) and uveitic (uERM) epiretinal membrane groups. Both cases were classified as Grade 2 ERM based on optical coherence tomography findings. Vector field analysis, using rigid and non-rigid registration techniques with retinal vessel segmentation, quantified and visualized changes after ERM surgery. (A–D) iERM case. (E–H) uERM case. (A,E) Preoperative fundus photographs. (B,F) Corresponding fundus images taken 6 months postoperatively. (C,G) Vessel probability maps showing preoperative vessels in red and postoperative vessels in blue. The overlay highlights vessel location changes, with red indicating preoperative positions and blue indicating postoperative positions. (D,H) Vector field images visualizing retinal displacement. Pixel-wise displacement was calculated by comparing preoperative and postoperative images. Displacement vectors, visualized every 25 pixels, are superimposed on the postoperative fundus images. These are illustrative examples and were not included in the quantitative analysis.

Fig. 3

Postoperative changes in retinal vascular geometry after ERM surgery. (A–D) Graphs showing changes in retinal arterial and venous angles at 1 and 6 months postoperatively, highlighting differences in the magnitude of change between the iERM and uERM groups. (E,F) Retinal arterial and venous tortuosity were higher in the iERM group preoperatively and showed a greater reduction postoperatively compared to the uERM group. Postoperative retinal arterial and venous angles increased over time, with significant differences in venous branch angles between the groups at all time points. Vessel tortuosity (both arterial and venous) decreased in both groups, with the iERM group showing a significantly greater reduction at 6 months.