THE EFFECT OF SPHERICAL AND OTHER ABERRATIONS UPON THE MODULATION TRANSFER OF THE DEFOCUSED HUMAN EYE

Relative modulation transfer is defined as contrast sensitivity under blur normalised to contrast sensitivity at optimum focus. Measured rel ative modulation transfer exceeds relative modulation transfer as calc ulated for aberration free optics at higher spatial frequencies (>2 cp d). The contribution of spherical aberration to this discrepancy was s tudied. In the case of positive blur, spherical aberration increases r elative modulation transfer for spatial frequencies of approximately 4 cpd and over. However, spherical aberration does not explain the enti re difference between measured and calculated relative modulation tran sfer. Chromatic aberration does not provide a noticeable additional ex planation. With negative blur, spherical aberration increases the rela tive modulation transfer much more. The effect of other monochromatic aberrations on relative modulation transfer is discussed. (C) 1998 The College of Optometrists. Published by Elsevier Science Ltd. All right s reserved.