The purpose of this study was to determine what type of refractive shift, if any, would occur as the result of enduring extreme physical fatigue. One hundred twenty-four marathon runners, and ten control subjects were measured with autorefractors before and immediately after the 26.2 mile Seattle marathon on November 27, 1993. The authors hypothesized that a significant shift in equivalent sphere toward hyperopia would occur due to the effects of dehydration, sympathetic activation, and possible loss of ciliary muscle tonus. The results indicate that there is no significant shift in refraction when compared to the controls, but individual subjects exhibited clinically relevant hyperopic or myopic shifts. Contact lens wearing subjects showed a statistically significant shift in refractive error towards myopia when compared to non-contact lens wearing subjects.
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