Effect of altered vision on constant load exercise performance while wearing a respirator.

Previous testing has shown that visual acuity greatly influences task performance at light work rate levels. At moderate to heavy work rates, however, the Performance Rating Table (PRT) predicts almost no visual acuity effect. This experiment was performed to determine if the PRT value is realistic. Ten subjects walked on a treadmill at 75-80% of their maximum heart rates until their voluntary end points. Subjects wore various masks of the same kind, each with a different set of clouded lenses. Visual acuities, as measured on the Snellen eye chart, were measured before, during, and after exercise. It was found that visual acuity did not influence performance time, and that an average value for a performance rating of 91 must have been influenced by other mask factors besides visual acuity. These other factors are most likely respiratory stress, thermal stress, and other vision elements. The full-facepiece masks used in this study adversely affected visual acuity by about three-quarters of a Snellen line during exercise. Postexercise visual acuities were found to first decrease below pre-exercise values, then become better than pre-exercise values, then decline asymptotically to pre-exercise values.