Photopic 30 Hz flicker electroretinography predicts ocular neovascularization in central retinal vein occlusion

Abstract

To confirm the predictive value of photopic cone b-wave implicit time in 30 Hz flicker electroretinography (ERG) for ocular neovascularization (NV) in central retinal vein occlusion (CRVO), and to compare the ERG results to the presumed healthy fellow eye. A retrospective analysis of 71 consecutive patients with CRVO. After ERG examination, all patients were followed for at least 12 months, or until NV was found. Three patients died during the study period; none of the other patients were lost to follow-up. Twenty-four patients (33.8%) developed NV during follow-up. The mean cone b-wave implicit time of all patients was 32.6 ms [standard deviation (SD) 5.21]. All 18 patients with an implicit time of 35.0 ms or higher (> 0.5 SD from mean) developed NV. In patients who developed NV, the average implicit time was 38.5 ms (range 29.7-43.9 ms); in patients without NV (n = 47), the average implicit time was 29.6 ms (range 24.7-34.9 ms) (P < 0.0001). The average implicit time in the presumed healthy fellow eye was 28.7 ms (range 24.4-33.9 ms) in patients with NV, and 26.5 ms (range 23.7-33.2 ms) in patients without NV (P = 0.002). The mean interocular difference in implicit time was 9.9 ms (range 4.1-15.7 ms) in patients with NV and 2.9 ms (range -1.0 to 10.0 ms) in patients without NV (P < 0.0001). Patients with CRVO should be examined routinely with photopic 30 Hz flicker ERG, which is a simple and objective clinical test that can identify patients at risk of ocular NV. On the assumption that the presented ERG settings are used, implicit times of 35.0 ms or higher (> 0.5 SD from mean) are clearly associated with the development of ocular NV. To compare the ERG result of the affected eye to the presumed healthy fellow eye is probably of less value.