Vision is a most acute human sense, so it is rather surprising that the very first step in the visual process—the formation of an image on the retina—is often defective. One reason is that the human eye has significant optical defects, aberrations, that distort the passing optical wavefront, blur the retinal image, and degrade our visual experience. Diffraction, which is caused by the finite size of the eye's pupil, is the other reason for blurri‐ness. Together, aberrations and diffraction limit not only what the eye sees looking out, but also determine the smallest internal structures that can be observed when looking into the eye with a microscope (see box 1 on page 33). Spectacles and contact lenses can correct the eye's major aberrations, but if all the aberrations could be quantified and corrected while, at the same time, minimizing diffraction, high‐resolution retinal microscopy could become routinely feasible—and we might eventually achieve supernormal vision.

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