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Multifocal electroretinography could help stage AMD treatment MULTIFOCAL electroretinography (mfERG) could offer a useful way to screen which age-related macular degeneration (AMD) patients would benefit from retreatment after photodynamic therapy (PDT), a Canadian study suggests. The measurement, which is non-invasive and doesn't take much time, could relieve part of the burden in ophthalmologists' offices by reducing the number of patients coming in for multiple retesting with fluorescein angiography and identifying those who may be appropriate for early retreatment. These are the hopes of Canadian researchers who did a preliminary trial investigating whether there is a correlation between multifocal electroretinography (mfERG) measurements of the central area of the retina and the presence of leakage post-PDT. "Measuring p1 latencies could be a way to help screen patients and see which ones should be seen faster by an ophthalmologist. It could also help determine who needs to be retreated," said Marie-Josée Fredette, MD, at the annual meeting of the Canadian Ophthalmological Society. Her group, led by Drs M. Hébert (electrophysiologist) and G. Lalonde (ophthalmologist) at the Centre Hospitalier Université Laval in Quebec city , conducted a study on 21 eyes of 20 patients with AMD. The patients had a mean age of 72 years, had predominantly classic choroidal neovascularisation (CNV) and underwent mfERG measurements before and after PDT. All measurements were taken in non-dilated eyes. The stimulus used was a 61 hexagon matrix with a mean luminance of 400 cd/m2. P1 latency was measured for each ring in the retina. Prior to PDT, the mean p1 latency was 39.05 milliseconds (ms). A total of 18 eyes (86%) had a p1 latency greater than 35.8 ms, higher than what would be seen in normal eyes. Three eyes had a p1 latency of less than 35.8 ms, that could be imputable to small paracentral membranes missed by the mfERG, Dr. Fredette said. A total of 13 eyes had improved p1 latency by 1.6 ms or more within the first two months post-PDT, with six having improved in the first month. Six eyes had no improvement in p1 latency. That correlated with leakage or with persistence of CMV on the angiogram, she said. With retreatment allowed every three months, mfERG demonstrated a significant improvement in p1 latency on the second and forth month of follow-up. She noted that ongoing studies seem to suggest that early retreatment may have advantages, but patients would need to undergo more frequent follow-up. MfERG has the potential to help screen patients for this. The researchers are continuing the work to see how closely mfERG correlates to findings on fluorescein angiography. "The goal is not to replace the angiogram but rather to assist AMD follow-up by enabling a closer follow-up and providing a screening tool to determine which patients should undergo earlier angiograms, for early retreatment for instance," she said. There were two key motivations for the study. One was to investigate whether a method less invasive than fluorescein angiography was feasible for closer follow-up, and the second was related to ophthalmologic manpower issues."All our patients undergo frequent fluorescein angiograms and frequent fundus evaluation by ophthalmologists who are already quite overwhelmed with all kinds of ophthalmologic evaluations in addition to their AMD patients. We wondered whether there might be some other technology to help follow-up AMD patients in a less invasive manner and in a less overwhelming way," said Dr. Fredette. "We wanted to try to determine latency criteria that could be used to establish which patients should see the ophthalmologist earlier with an angiogram in order to get retreatment," she added. Of the study, Vancouver ophthalmologist David Maberley MD said: "This is an interesting piece of supplemental information. But we need to take it in the context of the clinical examination including fluorescein angiography." He also does research with mfERG but is not a part of the Quebec research team. He said that the use of p1 latency possibly could define which patients would benefit most from PDT, but it would be very unlikely to replace angiography. Latencies cannot be used to predict who to retreat because we don't know what treating based on latencies will mean to outcomes, he noted. Marie-Josée Fredette MD
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