CHOICE OF REFERENCE AXIS IN OCULAR WAVE-FRONT ABERRATION MEASUREMENT

The geometrical center of the pupil has often been used as the referen ce axis in ocular wave-front aberration measurement. However, the geom etrical center of the pupil may shift when the pupil size changes unde r different conditions. In particular, for subjective methods, definin g the center of the pupil precisely during the actual measurement is n ot always practical. Furthermore, the geometrical center of the pupil may not define the chief ray of the ocular optics because of the Stile s-Crawford apodization effect, which has a peak location that often de viates from the geometrical center of the pupil. We present the coeffi cient transformation table of the Taylor polynomial up to the sixth or der with respect to reference axis shift. We illustrate the effect of wave-front aberration change with reference axis shift with experiment al data. This type of wavefront aberration change could be a true meas urement error if there is an error in defining the reference axis. We also propose using the coaxially sighted corneal reflex as a better re ference axis in aberration measurement. (C) 1998 Optical Society of Am erica.