How much vision impairment does it take to decrease performance in freestyle swimming?

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 vision impairment should be necessary to compete. Almost all sports presently require 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 and there is no evidence to suggest that this is a level of acuity that decreases sport performance. Moreover, the cut-off is likely to differ by sport. Accordingly, each sport could be including individuals without a disadvantage in the sport, or excluding those who do. The aim of this study was to establish the level of visual acuity loss that decreases performance in freestyle swimming. Twenty-one national level swimmers without vision loss swam 100m freestyle races 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. ROC analysis was used to establish the level of visual acuity that first 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 (82% sensitivity and 68% specificity). In general, performance was not impacted by lesser amounts of vision impairment. The findings suggest that the minimum level of impairment required to compete in swimming for athletes with vision impairment may need to change, because there may be athletes competing whose impairment does not decrease performance in the sport. The results are expected to contribute to a change in the classification rules to be used for swimming in the 2028 Los Angeles Paralympic Games.