Ocular accommodation and the virtual lens

This dissertation presents new type of feedback display, the virtual lens, that senses the accommodative state of the eye and uses that information to modify a visual display. The image processing effect of the lens--i.e. blurring--can be removed by placing an active, controllable, predistorting opto-mechanical system between subject and the display, and using accommodative state information to optically remove the effect of accommodation. Simultaneously, the accommodative state information can be used to modify the CRT image digitally, blurring it, for example, to simulate the effect of the (now optically removed) lens; thus the term virtual lens: the image processing action of the lens is optically removed, and replaced by digital image processing algorithms implemented in software. Chapter 1 describes the theory, design, and implementation of the virtual lens.;The capability of the virtual lens to measure dynamic accommodation and control both target distance and display image in real time also make it a general monocular accommodation workstation. Nearly all signal processing and control takes place in software, so very little hardware adjustment is needed. Chapter 2 describes a number of experiments: some are replications of classic experiments to show how these can be implemented on the virtual lens, others are new experiments that require the particular characteristics of the virtual lens to perform.;Chapter 3 is a theoretical analysis of defocus detection, taking existing engineering solutions to the problem of passive, image-based autofocus and examining their applicability to question of human ocular accommodation.;Chapter 4 describes how the lower and upper thresholds of the human blur detection mechanism, combine with different control modes to produce hysteretic behavior. We reconcile our findings with a different type of hysteretic behavior observed by Heath 30 years ago, and show how they are related.;Chapter 5 describes a study of the effects of wearing a head-mounted display (another type of feedback display) on the ocular accommodation response.