Near vision, lags of accommodation and myopia.

It is shown that, with some simplifying assumptions about the nature of the accommodation response/stimulus curve, geometrical optics predicts that lags in accommodation will result in ocular modulation transfer for any linear size of grating component in an object being independent of object distance. Thus bringing an object nearer to the eye should not improve the contrast of the retinal image of any of its details. However, when the effects of diffraction and aberration are considered, together with the angular spatial frequency dependence of the retinal contrast threshold, the expected advantages of short observation distances for the detection of fine detail emerge. It is shown that a reduced slope for the accommodation response/stimulus curve leads to increased lag and reduced modulation transfer: the possible role of such effects in the development of some types of myopia is discussed.