UC Berkeley

Purpose. Experiments in animals and the human have demonstrated axial length changes in the eye that depend on the direction of defocus and hence suggest a role of optical properties of degraded retinal images in the etiology of myopia. Methods. Retinal light distributions are calculated when targets removed by several diopters from optimal focus in both hyperopic and myopic directions are imaged in a typical normal human eye, using standard diffraction approaches. Results. Even as progressively more sophisticated factors are folded in – light in a wide spectral range, chromatic aberration, spectral acceptance curves of likely detecting substances in the retina and choroid, the Stiles-Crawford effect – equivalent hyperopic and myopic defocus conditions are shown to differ only minutely. Conclusions. That the distinction between retinal images of equivalent level but opposite polarity of defocus requires exquisite processing capabilities challenges the view that simple optical image properties provide the clue to changes in the eye’s axial length,