The effect of monochromatic aberrations on Autoref R-1 readings

The Canon Autoref R-1 is used extensively to investigate aspects of the acc ommodation response of the human eye. The measurement zone of the Autoref R -1 is known to lie outside the central pupil and the instrument's readings are therefore potentially influenced by the monochromatic aberrations of th e eye. Since these aberrations are known to change as a function of accommo dation, the error associated with the aberrations might influence the stimu lus-response slope. We used masks and contact lenses with known amounts of spherical aberration to establish the region of the pupil used by the Autor ef R-1 in deriving a reading of the refractive power of the eye. This regio n was estimated to be narrowly centred on a 3.5-mm diameter. The spherical aberration of the eye was measured for five subjects across a range of acco mmodation levels and used to predict the likely effect upon Autoref R-1 rea dings. Positive spherical aberration will result in an apparent lead of acc ommodation, while negative spherical aberration causes an apparent lag of a ccommodation. For eyes with normal levels of spherical aberration, the slop e of the stimulus-response will appear to be marginally flatter when measur ed with the Autoref R-1. An example of an eye with coma-like aberrations is also shown to produce Autoref R-1 results that will differ significantly f rom more central refractive measurements. (C) 2001 The College of Optometri sts. Published by Elsevier Science Ltd. All rights reserved.