Optical and neural factors contributing to age-related losses in spatial vision

摘要

Two studies were conducted to quantify neural factors contributing to age-related changes in spatial vision. First, high order aberrations (HOAs) were measured and corrected in the eye with adaptive optics (AO) while observers performed contrast sensitivity and visual acuity tasks. With a large pupil, AO improved spatial vision performance significantly more for older compared to younger observers. Despite this, performance remained lower for older observers. When age-related miosis was controlled, young and old observers experienced similar benefits of AO. Correcting HOAs may increase the relative impact of other optical factors for older observers, such as intraocular scatter, but the importance of neural factors was not ruled out. We then explored age-related changes in contrast gain related to the magnocellular and parvocelluar pathways, a direct neural correlate to spatial vision performance. Younger and older observers participated in discrimination tasks thought to probe the distinct contrast gain signature of each pathway (Pokorny & Smith, 1997). Model fits to the data revealed an age-related shift in gain slope and elevated thresholds for both pathways, although functional losses were greater for the P pathway under tested conditions. We conclude that age-related decline in spatial vision is the result of both optical and neural factors.