Monochromatic ocular aberrations in 108 eyes of a normal young population (n ¼ 59) were studied. The wave-front aberration were obtained under natural conditions using a near-infrared Shack–Hartmann wave-front sensor. For this population and a 5 mm pupil, more than 99% of the root-mean square wave-front error is contained in the first four orders of a Zernike expansion and about 91% corresponds only to the second order. Comparison of wave-fronts aberrations from right and left eye in 35 subjects, showed a good correlation between most of the second- and third-order terms and a slight (but not clear) tendency for mirror symmetry between eyes. 2002 Elsevier Science Ltd. All rights reserved.