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Background: Numerous studies have investigated the importance of visual clarity in simulated athletic performance and, surprisingly, have observed that several sports-related tasks are resilient to low-tomoderate levels of retinal defocus. The purpose of this study was to determine the effect of myopic defocus on baseball batting performance, as well as the influence of gender, preferred hand, refractive error, and previous baseball experience. Methods: Thirty visually normal (visual acuity at least 20/20, stereoacuity better than 50 arc seconds of stereoacuity) young-adult participants were pitched 20 baseballs from a pitching machine under four conditions in a randomized order: plano (control), +1.00 D, +2.00 D, and +3.00 D. All participants were tested under binocular viewing conditions, with their habitual distance correction in place. Two independent observers graded the batting performance via a quality-of-contact score. Results: Batting performance was significantly reduced under +2.00 D and +3.00 D conditions, but not under the +1.00 D condition. The overall effect of retinal defocus was significant (F = 9.137, p < 0.001). Previous baseball experience yielded a statistically significant difference in performance, but neither refractive error, hand, order, nor gender significantly influenced performance. A high linear correlation between both observers was found (R2 = 0.99). Conclusion: This study demonstrated that baseball batting performance was resilient to low levels of retinal defocus for amateur baseball players. The threshold level of myopic defocus where performance declined appears to be lower for baseball than for other simulated sportsrelated activities in the literature, including golf putting, cricket batting, and basketball free throws, suggesting that the influence of myopic defocus on athletic performance is likely task-dependent. [ABSTRACT FROM AUTHOR]