We determined the foveal optical modulation transfer functions of the human eye (O) for pupil sizes of 1-8 mm by using two simple psychophysical techniques. O as a function of spatial frequency f could be described by exp[-(f/fc)n] at any pupil size in our data as well as in the data available in the literature [J. Physiol. (London) 186, 558 (1966); Opt. Acta 21, 395 (1974); Vision Res. 33, 15 (1993); J. Opt. Soc. Am. A 11, 246 (1994)]. When all these estimates of fc and n were pooled the parameters were found to depend on the pupil diameter as fc = 16.6 - 1.49p and n = exp(0.840/p - 0.318). This result indicates that at 1 mm O(f) is close to the diffraction-limited system.