Potential Signal to Accommodation From the Stiles-Crawford Effect and Ocular Monochromatic Aberrations Available in the Shape of the Point Spread Function

Abstract

Purpose:: Correct accommodation has been observed in the absence of cues from even-error blur and chromatic aberration, and with 3-mm pupils, suggesting the presence of an ‘achromatic cue’ to accommodation. The purpose of this study was to determine if characteristic patterns in the intensity distribution of the defocused retinal image due to the Stiles-Crawford (SC) effect and the eye’s monochromatic aberrations can provide a signal to accommodation in these conditions.

Methods:: Full data were collected in the left eyes of 12 visually normal adult participants. The foveal SC function (10 min arc disc, 548 nm) was sampled psychophysically at 21 points within the natural 3-mm pupil. Ocular monochromatic aberrations through the fifth Zernike order were measured with a COAS aberrometer for a 2 D accommodative demand. The retinal image of a monochromatic 10.2-min arc disc for a 3-mm pupil was simulated in software. This was done for spherical defocus of -1 D, 0 D and +1 D, in each of four conditions: (1) Control, eye free of SC effect and aberrations; (2) SC condition, eye with SC effect but no aberrations; (3) aberration condition, eye with aberrations but no SC effect; and (4) SC + aberration condition, eye with SC effect and aberrations. Accommodation was recorded (100 Hz) in 20.48-s trials (6 per condition) in which participants viewed a low-contrast cross target followed by the monochromatic (548 nm) simulated disc target. Targets were viewed in a Badal optical system, though a 0.75-mm pinhole to ensure that accommodation and the eye’s optics could not influence cues available in the simulations, and to preclude even-error blur cues.

Results:: Accommodation did not differ significantly from that in the control condition for the SC condition (F = 0.32, p = .59), the aberration condition (F = 4.9, p = .052), or the SC + aberration condition (F = 1.4, p = .29).

Conclusions:: For a 3-mm pupil, characteristic patterns in the intensity distribution of the defocused point spread function due to the SC effect or monochromatic aberrations do not provide an ‘achromatic cue’ to accommodation.

Keywords: optical properties