| Sumario: | Paralympic sport provides tremendous opportunities for individuals with impairment, including vision impairment, but there is controversy about the fairness of competition. Particularly, it remains unclear how much impairment should be necessary to compete. Swimming for athletes with vision impairment presently requires athletes to have a visual acuity of at least 1.0 logMAR to qualify (20/200 or 6/60), though this cut‐off is based on the legal definition of low vision, with no evidence to suggest it decreases swimming performance. Accordingly, swimming might currently include individuals without a disadvantage, or exclude those who do have a disadvantage. The aim of this study was to establish the level of visual acuity loss that decreases performance in swimming. Twenty‐one national‐level swimmers without vision impairment swam 100 m freestyle maximal effort time trials in each of four different levels of vision impairment simulated using plus lenses (plano, +4.00, +6.00, +8.00). Visual acuities ranged from −0.3 to +1.6 logMAR (an acuity of 0.0 logMAR would typically be considered to represent "normal" vision, a negative value better than "normal", and a positive value worse. For reference, under the existing system of classification for VI swimming, an acuity of 1.0 logMAR would qualify an individual to compete in the S13 class, an acuity of 1.5 logMAR in the S12 class, and an acuity worse than 2.6 logMAR for the S11 class). ROC analysis and repeated‐measure decision tree were used to establish the level of visual acuity that brought performance below what would be expected by normal variation. Results revealed that a cut‐off of at least 1.1 logMAR provided the optimal classification of performance as below‐expected performance. In general, performance was not impacted by lesser amounts of vision impairment. The findings suggest that the existing minimum level of impairment required to compete in swimming is close to being appropriate, but that the current threshold may be slightly too low. The results are expected to contribute to the introduction of evidence‐based classification rules to be used for swimming in the future Paralympic Games.
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