Nguyen MT, et al. – Analysts ascertain the between–visit repeatability of refractive error and higher–order aberration measurements with the Discovery System and aim to inspect between–instrument agreement of refractive error measurements with the Discovery System and Grand Seiko WAM–5500 open–field autorefractor (Grand Seiko Co., Hiroshima, Japan). The Discovery System was very repeatable and would be an appropriate instrument to measure cycloplegic refractive error and higher–order aberration changes in adults. There were small differences in refractive error between the Discovery System and Grand Seiko.