Eye (1 991) 5, 362-368 Electroretinography as a Prognostic Indicator or Neovascularisationin CRVO A. J. MORRELL*, D. A. THOMPSON,t J. M. GIBSON*, E. E. KRITZINGER*, N. DRASDOt Birmingham Summary A prospective study was carried out to compare the efficacy of electroretinography, fundus fluorescein angiography and clinical examination in identifying those at risk of rubeotic glaucoma following central retinal vein occlusion (CRVO). Our prelimi­ nary observations are described. The findingssuggest a complementary role for elec­ troretinography in the management of CRVO. Particularly significant were interocular differences in 30Hz flicker latency, the ability to elicit pattern ERGs and the ratio of scotopic and photopic a: b w�ve amplitudes. Of the clinical measures the depth of the relative afferent pupil defect was a sensitive indicator of rubeosis. Fac­ tors oflesser statistical prognostic value included poor visual acuity and the extent of deep retinal haemorrhages. Fundus fluorescein angiography in this study had lim­ ited value in predicting those patients at risk of rubeosis. The development of neovascularisation and develop complications.7 This largely reflects secondary glaucoma is a significantcomplica­ the limitations of fundus fluorescein angio­ tion of central retinal vein occlusion (CRVO) graphy: assessment of the degree of retinal occurring in 17-33% of patients.1,2,3 It is non-perfusion on the angiogram can be tech­ essential that those patients who are at risk of nically difficult due to factors such as small developing new vessels are identified at an pupil size, media opacities and the presence of early stage as prophylactic laser pametinal extensive deep retinal haemorrhages obscur­ photocoagulation has been shown to be effec­ ing the retinal circulation. Even with good tive in eliminating the neovascular quality angiograms inconsistencies of inter­ response.4,5 pretation occur amongst experienced It has been suggested that the stimulus for observers.8 new vessel growth is a vasoproliferative factor New vessel growth in venous occlusion is released by ischaemic retina.6 At present considered to be a response to hypoxia rather clinical and fluorescein angiographic features than retinal cell death.1,2,6 Fluorescein angio­ are used to determine the degree of retinal graphy identifies under-perfused areas of ret­ ischaemia present and to predict those eyes ina, but these may be either hypoxic or which will develop neovascularisation. How­ infarcted retina. It is possible that the elec­ ever, these methods lack specificity,and result troretinogram (ERG), which can distinguish in the prophylactic treatment of a much larger decreased retinal sensitivity from non-func­ number of patients than would be expected to tioning retina, may be a better means of pre- From: *Birmingham and Midland Eye Hospital, Birmingham UK, tVision Sciences, Aston University, Birmingham, UK. Correspondence to: A. J. Morrell, Birmingham and Midland Eye Hospital, Church Street, Birmingham B3 2NS. ELECTRORETINOGRAPHY AS A PROGNOSTIC INDICATOR OR NEOVASCULARISATIONIN CRVO 363 dicting neo-vascularisation. The a- and b­ cular disorders were excluded. The mean age wave components of the ERG respectively of the group was 61 years, range 29-87 years. reflect the functional integrity of the recepto­ All patients were seen in the Medical Oph­ ral and inner nuclear layers, which in turn thalmology Clinic within three weeks of pres­ depend upon differing blood supplies. Some entation for clinical assessment and fundus earlier studies of the ERG in CRVO have fluorescein angiography. Electroetinography demonstrated that patients with non-perfused was carried out with 7-12 days of (usually CRVO, had reduced b/a wave amplitude prior to) the fundus fluorescein angiogram. ratios.9,10 It is possible this ratio may be a sen­ Informed consent was obtained from all sitive index of perfusion from the retinal cir­ patients entered into the study: (one patient culation, because of the differential locus of refused consent for fluorescein angiography generation of the two waves: the b-wave being due to a fear of injections). the more proximaL However, these findings Methods gave only an approximate indication of sub­ sequent neovascularisation. Other recent Clinical Assessment reports have suggested ERG latencies, which Examination, undertaken by an observer who reflect retinal sensitivity, may be useful addi­ was unaware of the ERG results, included tional indicators of new vessel for­ slit-lamp microscopy, intraocular pressure mation.11.12,13 measurement, gonioscopy, fundoscopy and The ERG evoked by a pattern stimulus colour fundus photography. The following (PERG) is considered to have an even more features were recorded: visual acuity, the proximal retinal origin than the scotopic number of fundal cotton wool spots, the b-wave, 14,15 It might therefore register signs of extent of deep retinal haemorrhages, the a compromised retinal circulation earlier than presence of macular oedema, retino-ciliary a flash evoked ERG. collateral vessels and iris or retinal new The PERG is a localised test of central ret­ vessels. If present a relative afferent defect inal function and would not reflect the total was quantified using neutral density filters.1 7 extent of hypoxia present in the retina. How­ Fundus Fluorescein Angiography ever Magargal et al. 16 has suggested that broad Fluorescein angiography was performed with zones of capillary nonperfusion extend from a 50° fundus camera taking sequential views of the posterior pole to the retinal periphery. the posterior pole and the mid-periphery of Should this be the case then the PERG, by the retina. Significant ischaemia was defined sampling the posterior pole region, might be as greater than 50% capillary non-perfusion an index of the total amount of retinal ischae­ of the total retinal visible on the fluorescein mia and thus be related to the likelihood of angiogram and/or disruption of the perifoveal subsequent neovascularisation. arcade. The aim of our study was to compare the efficacy of both flash and pattern electroreti­ Electroretinography nography with currently employed clinical PERG recordings are demanding for the and fluorescein angiographic methods as a patient, requiring steady fixation and focus. prognostic indicator of neovascularisation in The total ERG protocol was therefore patients with recent onset CRVO. designed to minimise patient chair time: a recording session including flash and pattern Patients and Methods ERGs typically took 1-1.5 hours. Expendable DTL fibre corneal electrodes in detachable Patients holders18 were referred to EEG cup elec­ Forty-three consecutive patients, who pre­ trodes positioned on the ipsilateral temporal sented to the Birmingham and Midland Eye bone. Binocularly evoked responses were Hospital casualty department between averaged on a Nicolet Pathfinder and stored December 1988-Decmber 1989 with uni­ on magnetic media for subsequent analysis. ocular CRVO, were recruited. Fellow eyes were examined and patients with bilateral Flash ERGs ocular involvement or other major retinal vas- Opaque diffusing goggles were used to distri- 364 A. J. MORRELL ET AL. bute evenly the light flashes emitted by a Patients were followed in clinic for a mean Grass Strobe. Photopic ERGs were recorded of 7.8 months (range 4-14 months), with the to flash intensities 2, 4, 8 and 16. 10-20 exception of one patient who died at two responses were averaged between a bandpass months. Eight of 41 patients developed of 0.5-250Hz. Oscillatory potentials were fil­ rubeosis iridis within a mean of 10.4 weeks tered offline, between ISO-250Hz, from the (range 3-20 weeks) from the estimated date of photopic response to flash intensity 16. A onset of CRVO. Three of these eight patients 30Hz flicker response was elicited by flash also developed new vessels on the disc. For intensity 8 and 20 averages recorded between subsequent analysis the patients were divided a bandpass of 0.5-70Hz. Single flash scotopic into rubeotic and non-rubeotic groups. The ERGs were obtained after a minimum of 15 initial ERG data and clinical findings were minutes dark adaptation to flash intensity 8. compared across the two groups to find the tTwo patients were unable to tolerate the dark most sensitive predictive factor of rubeosis . adaptation period because of claustrophobia even though the subject room was sizeable Clinical Assessment Results and a bowl stimulus was not used]. Relative afferent pupil defect All patients were examined for the presence Pattern ERGs of a relative afferent pupil defect (RAPD). Four black and white chequerboard patterns Twenty patients were found to exhibit a were used with decreasing effective retinal defect, including all eight rubeotic patients. contrast. They were back-projected onto a The RAPD was quantifiedin 16 patients, but circular screen of mean luminance 250 cd/m2• not in four of the patients who subsequently Stimulus contrast was 75%. The patterns became rubeotic. The presence and magni­ were presented in order of decreasing retinal tude of the RAPD was a sensitive method of contrast: differentiating the two groups of patients The first two patterns were counterphased at (Mann-Whitney test, P<0.0005). 4Hz: 1. A chequerboard subtending 5° 30' Visual acuity 2. A chequerboard subtending 30' In order to include measures of PL, HM and The remaining two patterns were presented CF, visual acuities were grouped into three in onset/offset mode, appearing for 125msec bands: «6/60), (6/60-6/18) and