"Long-term objectives are to identify optical signals that control accommodation and emmetropization of the eye, and to identify the mechanisms that mediate the optical signals. A primary goal is to determine whether accommodation responds to the wavefront characteristics of light [defocus and higher-order aberrations (HOAs)], without feedback from change in defocus astigmatism or HOAs. Accommodation, pupillary responses and aberrations will be monitored by an imaging simulator that incorporates Hartmann-Shack wavefront sensing, adaptive optics and Hirschberg x-y eye tracking. Adaptive optics and Badal optics will compensate for the refractive error of the eye, alter or remove HOAs, and remove feedback from changes in accommodation and/or HOAs. Accommodation will be driven by defocus with normal HOAs present or removed. To determine whether accommodation responds to wavefront aberration per se, or simply to the shape or skewing of blur, aberrations will be removed while simulation of defocus targets are imaged on the retina, with and without the effects of HOAs on the blur. Standard model that accommodation operates as a closed-loop negative feedback system to maximize the contrast retinal image, will be tested by using adaptive optics to remove defocus, astigmatism and HOAs and by establishing a closed feedback loop between accommodation and target contrast. An alternative hypothesis that accommodation responds to wavefront defocus rather than blur of the retinal image, will be tested by driving accommodation with defocus without feedback from blur, in the absence of HOAs. A final experiment will determine whether the pupil changes independently of lenticular accommodation to provide better acuity in the presence of spherical aberration. Better understanding of the optical signals and mechanisms that the eye used to detect myopic and hyperopic defocus may lead to early detection of individual at risk for developing myopia, and new treatments to prevent/reduce myopia"