Resolution of blur in the older eye: neural compensation in addition to optics?

This study examined the roles of pupillary miosis and experience-mediated compensation in older observers' superior ability to read optically blurred text. The size thresholds of younger and older adult observers for reading common words and identifying line drawings of everyday objects were compared with natural and artificial pupils as a function of systematically varied far letter acuity: best corrected, 20/30, and 20/40. With best corrected letter acuity, younger observers' size thresholds for reading words were lower than those of older observers with either natural or artificial pupils. In the 20/40 condition, however, older observers' reading size thresholds with natural pupils were significantly lower than those of the young. No significant age differences were seen at 20/30 or 20/40 on word reading with artificial pupils or on line drawing identification size thresholds with either pupil type. Prior blur experience, as estimated from observers' presenting and best optical corrections, was inversely associated with older adults' word acuity. Pupillary miosis in conjunction with neural compensation appears to account for older observers' greater ability to read blurred text.