Correlation between inner retinal disorganization and macular ischemia in patients with center involved diabetic macular edema

Abstract

Purpose: Previous studies have shown that inner retinal disorganization (IRD) length measured on spectral domain optical coherence tomography (SDOCT) is highly associated with best corrected visual acuity (BCVA) after resolution of center involved diabetic macular edema (ci-DME). The purpose of this study was to investigate the relationship between IRD measured on SDOCT and foveal avascular zone (FAZ) size as a measure of macular perfusion using fluorescein angiography (FA) in patients with ci-DME.

Methods: This was a cross-sectional study that included patients with ischemic and non ischemic ci-DME who underwent BCVA testing, SDOCT and FA imaging. The diagnosis of ischemic DME was determined by the presence of irregular FAZ margins or enlarged FAZ. Both FA and SDOCT images were graded in a masked fashion. Using Adobe Photoshop, the FAZ area was measured and referenced to the size of the optic nerve to account for any variability in the FAZ size due to refractive errors. The length of IRD (defined as the inability to distinguish the boundaries between the inner retinal layers in the central 1500 µm) was measured in the corresponding SDOCT image.

Results: Thirty seven eyes of 25 patients were evaluated. Logmar VA was 0.40±0.20 (Mean ± SD), and central subfield thickness (CST) was 433±125µm. Mean age was 63±10 years. 60 % of eyes had non ischemic (22 eyes) and 40% (15 eyes) had ischemic DME. The FAZ/ON ratio [95%CI] in eyes with ischemic DME was 0.61 ± 0.12 [0.5, 0.7] vs. 0.15 ± 0.04 [0.1, 0.2] in eyes with non ischemic DME. Regression analysis showed a high association between IRD length measured on SDOCT and the corresponding FAZ/ON ratio on FA (R² = 0.36, P = 0.0002). Logmar VA [95%CI] in eyes with IRD was 0.5 ± 0.2 [0.4, 0.6] (N=27 eyes) vs. 0.1 ± 0.13 [0, 0.2] (N=10 eyes) in eyes with no IRD (p < 0.001). IRD length [95%CI] was significantly higher in eyes with ischemic DME, 794 ±321µm [609, 863] (N=15 eyes) vs. 362 ± 115µm [335, 397] (N=22 eyes) in eyes with non ischemic DME (p = 0.002). There was no significant correlation between CST and FAZ/ON ratio (R²= 0.12), however there was a strong correlation between IRD length and CST (R²= 0.46, P < 0.0001).

Conclusions: Foveal ischemia appears to contribute to the appearance of IRD on SDOCT in patients with ci-DME. If validated in further prospective studies, it can help explain the poorer visual outcome in patients with IRD.

Keywords: 550 imaging/image analysis: clinical