Normalized Reflectivity of Middle Limiting Membrane on SD-OCT: A Measure of Acute Ischemia in CRVO

To validate the quantification of the prominent middle limiting membrane (PMLM) sign, a marker of mild-to-moderate acute ischemic damage on optical coherence tomography (OCT), by measuring middle limiting membrane (MLM) reflectivity in patients with central retinal vein occlusion (CRVO) and to investigate the prognostic impact of this measure. Spectral Domain (SD)-OCT B-scans of 30 patients with CRVO, either sole CRVO or combined central retinal artery and vein occlusion (CCRAVO), were analyzed retrospectively and graded as PMLM present or absent. Normalized MLM reflectivity was calculated as a ratio of the maximum reflectivity within a MLM target layer and the average reflectivity of the retinal pigment epithelium (RPE). Discrimination between OCT B-scans graded as PMLM present or absent based on ROC analysis was far superior with normalized MLM reflectivity (AUC >0.90) than using MLM reflectivity without normalization (AUC = 0.70). Normalized MLM reflectivity was significantly higher in study eyes than healthy fellow eyes as well as in patients with CCRAVO versus sole CRVO. Although normalized MLM reflectivity correlated significantly with baseline and outcome BCVA, we found no significant difference comparing patients with ischemic CRVO versus non-ischemic CRVO. Quantifying MLM reflectivity requires normalization due to shadowing, which is usually caused by retinal haemorrhages in CRVO. RPE reflectivity proved to be a suitable reference layer. Greater normalized MLM reflectivity as a measure of mild-to-moderate acute ischemic damage indicated a worse prognosis regarding visual function in CRVO, however, it allows no risk assessment regarding the development of capillary non-perfusion or anterior segment neovascularization.