Head And Eye Movement Patterns During A Proffreading Task.

Recently there has been growing interest in developing progressive addition spectacle lenses that are the "best" at satisfying the needs of a large number of users (Pope). Most PAL-wearers are instructed to " lead with your chin" and otherwise alter their natural head, eye, and neck postures to utilize the lenses appropriately. It seems logical that a spectacle lens company would desire to produce a lens that would provide clear vision at all usual distances and directions of gaze while the user maintains his or her natural head, eye, and neck postures. Such a lens would be a clear advantage over those in existence today that require some training time before the lens can be fully effective. The questions that necessarily need answers before any discussion of a new lens design can occur are these: Does a predictable head and eye movement pattern exist for a given person during common tasks? If so, is this pattern consistent across people with similar accommodative states (i.e. similar age groups)? If the answer to either of these queries is "No", then there is little reason to pursue design research that will produce a lens that will satisfy a person with one particular movement pattern. Each patient would require a custom-made lens that allows for his or her unique head and eye movement strategies. It goes without saying that this would be a prohibitively expensive endeavor. Past research by Malinov et al. indicates that subjects prefer saccadic eye movements that are smaller than 15 degrees. Work by Lee suggests that people regularly combine head and eye movements. Studying the simultaneous use of the head and eyes gives a more accurate picture of a given person's visual habits. The present study was designed to measure head and eye movements during a particular proofreading task for a group of age-matched subjects, then to compare the results between and within subjects. The rationale for studying a reading task, rather than tasks at intermediate or far distances, is that conscious postural modifications while using a PAL occur most frequently during near tasks. This study is the first in a three-part research project to compare results across three different age groups.