The effect of monochromatic aberrations on Autoref R-1 readings

The Canon Autoref R-1 is used extensively to investigate aspects of the accommodation 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 the eye. Since these aberrations are known to change as a function of accommodation, the error associated with the aberrations might influence the stimulus-response slope. We used masks and contact lenses with known amounts of spherical aberration to establish the region of the pupil used by the Autoref R-1 in deriving a reading of the refractive power of the eye. This region 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 accommodation levels and used to predict the likely effect upon Autoref R-1 readings. Positive spherical aberration will result in an apparent lead of accommodation, while negative spherical aberration causes an apparent lag of accommodation. For eyes with normal levels of spherical aberration, the slope of the stimulus-response will appear to be marginally flatter when measured 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 from more central refractive measurements.