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In reply
As Dr Brigell knows, we evaluated the feasibility of including PVEPs as an outcome measure in the ONTT before initiating patient recruitment in 1988. We found many different PVEP instruments and data acquisition parameters in use at participating institutions. We had no confidence that we would be able to obtain reliable and valid results. We determined that standardization of equipment and technique would require extensive effort and considerable cost, which could not be justified by the knowledge to be gained from PVEPs in relation to the primary study objectives.However, an ONTT committee actively pursued the challenging logistics of standardizing PVEP parameters. Several of our centers participated with Dr Brigell in a pilot study supported by the National Eye Institute (Bethesda, Md) that was designed to evaluate methods for obtaining multicenter PVEP measurements. This study (unpublished data, 1993) demonstrated that uniform parameters for data acquisition could be established