The purpose of this work was to characterise short-(S)-wavelength-sensitive-cone mediated contrast sensitivity (CS) across twenty symptom-free subjects and eight asthenopics, all with normal-unaided-or-corrected visual acuity with no sign of oculomotor dysfunction. Threshold contrast sensitivity was assessed by the von Békésy tracking method from a viewing distance of 2.4 m (0.40 D). Three counterbalanced tasks required central fixation of black-and-white square-wave gratings (1, 5, 10, 14, and 17 cycles deg^-1) presented through a low-pass (400 - 450 nm) tinted blue lens: through (i) a 0.0 D lens, (ii) a -1.50 D lens, (iii) a +1.50 D lens while attempting volitional accommodation to minimise blur. Baseline increases in eye-strain, which approached high levels at the end of the experiment, did not differentiate between the two groups of volunteers. Compared with symptom-free subjects, asthenopics exhibited larger magnitudes CS performance in the intermediate spatial frequencies during experimental conditions requiring voluntary increases in accommodation. The residual filtered light may encompass reference wavelengths habitually used by the asthenopics in retinal alignment as an adaptive strategy to spare accommodation from eye-strain. Alternatively, asthenopics, owing to inherent retinal factors, may 'drive' their accommodative system harder than symptom-free subjects.[Supported by the Swedish Council for Working Life and Social Research Grant 2005-0488 to HR.]