Cone erg subnormality to red flash in central retinal vein occlusion: A predictor of ocular neovascularization?

Abstract

were re-evaluated 6-55 months later to determine whether ocular neovascularisation had developed. Of the 21 CRVO eyes, 6 (29%) were subnormal to red in the affected compared with the normal fellow eye. At follow-up, all 6 (100%) patients had developed ocular neovascularisation compared with 1 (7%) of the 15 patients who were supernormal to red (p = 0.00013).Cone ERG subnormality to red flash in CRVO eyes compared with normal fellow eyes may be a predictor of later development of ocular neovascularisation.Central retinal vein occlusion (CRVO) is a common retinal disease. 1 Follow-up studies of patients with CRVO have shown that 20-30% of patients may develop neovascularisation of either the iris, the anterior chamber angle or optic nerve. 1 -4 The stimulus for anterior segment and retinal neovascu larisation, although poorly understood, is thought to be related to severe retinal ischaemia. 5 For those patients with iris neovascularisation, early pametinal laser photocoagulation is effective in causing ocular neovascularisation to regress, while delayed photo coagulation usually results in a painful blind eye. 6 -10 Various clinical, l1 angiographic 5 , 12 and electrore-.h ' 1 3 -18 tmograp IC parameters have been used to predict which patients are at risk of developing ocular neovascularisation. However, none of them has been shown to be either sensitive or specific enough to identify all CRVO eyes in which neovascularisation will develop.We have previously reported that in most patients with CRVO, the amplitude of the cone electroreti nogram (ERG) b-wave is larger in the affected compared with the unaffected eye if the retina is sufficiently light-adapted and the test stimuli are of long wavelength. I9 We have called this 'supernorm ality to red'. This supernormality is unexpected since CRVO has usually been reported to decrease the amplitude of the flash ERG. 13 -15 , 18 , 20 , 21 We also observed that a minority of CRVO eyes, however, do not show this ERG supernormality to red flashes. In fact, they are subnormal to red in the affected compared with the unaffected eye, i.e. the ratio of the cone ERC b-wave amplitude to red in the CRVO eye to that in the normal fellow eye was less than l. In order to further elucidate the significance of differences in cone ERG responses to red in CRVO eyes, we decided to do a follow-up study of patients who had undergone an ERG at the time of diagnosis of the vein occlusion. We hypothesised that CRVO eyes which showed cone ERG subnormality to red flash compared with normal fellow eyes (ratio <1) would later develop ocular neovascularisation. The purpose of this paper is to report our findings. SUBJECTS AND METHODSIncluded in the study was a consecutive series of patients with unilateral CRVO and no abnormality of the fellow eye recruited from among patients either attending the general or retina clinics or referred by private physicians for an ERG. At the time the ERG was obtained, none of the patients had any evidence of neovascularisation of either the

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

“…1991a, 1991b; Johnson & McPhee 1993; Severns & Johnson 1993; Larsson et al. 1998a; Roy et al. 1998; Moschos et al.…”

“…Assessment of retinal nonperfusion by fluorescein angiography has been the standard method for classifying CRVO for a long time (Hayreh 1976;Laatikainen & Kohner 1976). However, because of difficulties in fluorescein angiographic evaluation and the definition of retinal ischaemia, several studies have shown that electroretinography (ERG) is a more suitable method to classify CRVO and predict ocular NV (Sabates et al 1983;Johnson et al 1988; Kaye & Harding 1988;Breton et al 1989;Sakaue et al 1989;Breton et al 1991aBreton et al , 1991bJohnson & McPhee 1993;Severns & Johnson 1993;Larsson et al 1998a;Roy et al 1998;Moschos et al 1999). Although most ERG responses change after CRVO, the implicit time is considered to be one of the best predictive parameters of ocular NV.…”

Supernormal Flicker ERGs in Eyes With Central Retinal Vein Occlusion: Clinical Characteristics, Prognosis, and Effects of Anti-VEGF Agent

“…Roy et al 23 also studied the prognosis of CRVO eyes with supernormal cone ERG amplitudes elicited by red flashes. They reported that only 1 of the 15 patients (7%) who had supernormal cone ERGs developed ocular neovascularization, whereas all 6 patients with subnormal cone ERGs developed ocular neovascularization.…”

Rod and Cone a-Waves in Central Retinal Vein Occlusion

“…Supernormal cone responses (both a-and b-waves) in eyes with CRVO have been described in several papers. 21,22 This phenomenon has been reported to involve the long-more than the middlewavelength-sensitive cones but not the short-wavelengthsensitive cones or rods. 22 Supernormal cone responses in all 12 cases could be detected using red flash, although 4 of the 12 cases also showed supernormal cone responses to white flash.…”