Visual function and adaptation across the lifespan

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Human beings rely heavily on visual function for activities of daily living and large portions of the brain are dedicated to visual function. It is therefore not surprising that visual impairment is one of the most highly feared disabilities. Fortunately, the eyes and visual system appear to be capable of adaptation to a variety of environmental influences opening the possibility of favorably altering outcomes, thus preventing or reducing visual impairment. Virtually every metric of visual function has a period of development to a maximum which subsequently declines into old age. However, for many aspects of visual function the development and decline are not well understood. For example, many preventative therapies for slowing the progression of myopia have been explored without success, reflecting the fact that the basic mechanisms which underlie refractive development are still unknown. My work in this area is aimed at understanding these mechanisms, a necessary step before one can reasonably expect to develop strategies for prevention or reversal. One of the breakthroughs of which I have been a part was the discovery that eyes grow in length to match their point of focus. This means that we should be able to control eye growth by controlling the focus of the eye, but we still don’t know how the eye knows whether to grow larger or smaller. Part of this proposal is to test, in an animal model, how three possible optical eye growth signals respond to lenses which either make the eye grow longer or shorter. Typically, children and the elderly have been neglected, in comparison to young adults, when investigating visual function, probably because it is difficult to do. A major portion of this proposal is to investigate visual functions across the range of the human lifespan. In particular, the plan is to take measurements of eye size, shape, focus, coordination and movement for a large number of individuals over this age range, using similar methods for all individuals. In this way we can study how the various factors interact and how this changes with age. Increasing our understanding of these processes should lead to strategies for optimizing development and reducing or compensating for decline. The implications of this are significant. For example, the development of eye coordination impacts learning in children and the loss of stereopsis puts the elderly at increased risk of falling which in turn puts their independence, if not their lives, at risk. Finally, not only are the various aspects of vision not independent of each other; they are also affected by such things as attention and the context of the situation. Here again children and the elderly are not as well studied and appear to behave differently than young adults. Using eye movement measurements to different types of targets and giving participants different instructions we will determine age related differences in their ability to quickly and accurately respond. It is important that age related normal values are known since the influence of attention and/or inhibition on eye movements may affect how diseases are diagnosed (e.g. Alzheimer’s disease, schizophrenia, ADHD).