Accommodation with higher-order monochromaticaberrations corrected with adaptive opticsLi ChenCenter for Visual Science, University of Rochester, Rochester, New York 14627Philip B. KrugerSchnurmacher Institute for Vision Research, State College of Optometry, State University of New York, 33 West42nd Street, New York, New York 10036Heidi Hofer*Center for Visual Science, University of Rochester, Rochester, New York 14627Ben SingerCenter for the study of Brain, Mind and Behavior, Princeton University, Princeton, New Jersey 08544David R. WilliamsCenter for Visual Science, University of Rochester, Rochester, New York 14627Received February 23, 2005; revised manuscript received June 9, 2005; accepted June 21, 2005Higher-order monochromatic aberrations in the human eye cause a difference in the appearance of stimuli atdistances nearer and farther from best focus that could serve as a signed error signal for accommodation. Weexplored whether higher-order monochromatic aberrations affect the accommodative response to 0.5 D stepchanges in vergence in experiments in which these aberrations were either present as they normally are orremoved with adaptive optics. Of six subjects, one could not accommodate at all for steps in either condition.One subject clearly required higher-order aberrations to accommodate at all. The remaining four subjects couldaccommodate in the correct direction even when higher-order aberrations were removed. No subjects improvedtheir accommodation when higher-order aberrations were corrected, indicating that the corresponding de-crease in the depth of field of the eye did not improve the accommodative response. These results are consistentwith previous findings of large individual differences in the ability to accommodate in impoverished conditions.These results suggest that at least some subjects can use monochromatic higher-order aberrations to guideaccommodation. They also show that some subjects can accommodate correctly when higher-order monochro-matic aberrations as well as established cues to accommodation are greatly reduced. © 2006 Optical Society ofAmericaOCIS codes: 330.5370, 010.1080, 330.5510.1. INTRODUCTIONThe accommodative mechanism of the eye uses many cuesto focus the retinal image of objects at a wide range ofviewing distances.1,2The natural visual environment isrich in cues, allowing accommodation to respond in theappropriate direction to focus the retinal image with veryrare errors. Cues that provide unambiguous informationabout the appropriate direction of the accommodative re-sponse include binocular disparity, familiarity, and a hostof other depth cues.3–5There is also substantial evidencethat many subjects can use the eye’s aberrations to ac-commodate in the correct direction. For example, longitu-dinal chromatic aberration (LCA) provides an odd-errorsignal in that it specifies the direction of accommodationthat will bring the retinal image into focus.5–14However,LCA is not the only stimulus to reflex accommodation. Itis well known that many subjects can accommodate tochanges in target vergence even when the target isviewed in monochromatic light to eliminate a cue fromLCA.15Whether or not retinal blur provides an odd-errorstimulus with both magnitude and sign of defocus14de-pends on whether the eye is aberrated. When there are nohigher-order aberrations and astigmatism at all, a stepchange of defocus from the focused retinal plane to thefront of retina (far step) and the same step change of de-focus from the focused retinal plan to the back of retina(near step) produce identical point-spread functions (PSF)on the retina, so that defocus itself does not provide infor-mation about the direction of accommodation.However, the eye suffers from higher-order aberrationsbesides defocus and astigmatism. Spherical aberration3,5and uncorrected astigmatism,3,16,17as well as other mono-chromatic aberrations,18provide odd-error cues to accom-modation because they cause differences in the appear-ance of stimuli depending on whether there is a far or anear step of defocus. Wilson et al.18showed that subjectsChen et al. Vol. 23, No. 1/January 2006/J. Opt. Soc. Am. A 11084-7529/06/010001-8/$0.00 © 2006 Optical Society of Americacould see these differences in PSF subjectively, andtrained them to use the visible information as a cue to de-termine whether the light is focused in front of or behindthe retina. We set out to determine whether the subjectactually uses this visible information when they accom-modate.Another viewpoint suggests that higher-order aberra-tions in the eye could hinder the accommodation responsebecause the depth of focus is larger when higher-order ab-errations are present.19–22The effect of correcting higher-order aberrations is to reduce the eye’s depth of focus. Forobjects that lie nearer to or farther from the plane of fo-cus, image quality can actually be worse than it is whenaberrations are left uncorrected. If accommodation relieson the rate of change of focus, then the speed and accu-racy of the accommodative response could actually be im-proved when higher-order aberrations are removed.In this paper, we investigate whether higher-order ab-errations affect accommodation in an experiment inwhich these aberrations were either present as they nor-mally are or greatly reduced with adaptive optics (AO).2. METHODSA. SubjectsAccommodation measurements were made on the righteyes of six subjects. The subjects ranged in age from27 to 37 years old. Refractive error of the subjects rangedfrom +1 D to − 3.5 D and astigmatism was less than 1 D.The subject’s head was stabilized with a bite-bar. The AOsystem used a 6 mm entrance pupil, requiring the dila-tion of the subject’s pupil with phenylephrine hydrochlo-ride (2.5%). This drug was chosen to dilate the pupil whileminimizing any effect on accommodation. Each subject’sconsent was obtained according to the declaration of Hel-sinki.B. Wave Aberration Measurement and CorrectionSubjects viewed a stimulus from a digital light projectorthrough the AO system shown in Fig. 1. This system23used a Shack–Hartmann wavefront sensor, conjugatewith the subject’s pupil plane, to make measurements ofthe eye’s wave aberrations at 30 Hz. The Shack–Hartmann wavefront sensor had 221 lenslets in squarearray that could measure the aberrations for a 6.8 mmpupil up to the tenth radial order. The wave aberrationmeasurements were made at a wavelength of 810 nm. Adeformable mirror with 97 lead