Ocular accommodation, personality, and autonomic balance.

The autonomic nervous system is made up of two subsystems: the parasympathetic (PNS) and the sympathetic (SNS). The balance between these systems regulates bodily functions during routine (PNS-dominant) and crisis (SNS-dominant) situations. It may also control visual accommodation: PNS activation for inward focus, and SNS activation for outward focus. Near- and far-sighted persons have been characterized as introverted and extraverted, respectively. These personality characteristics have been linked to autonomic balance: introversion and PNS-dominance, extraversion and SNS-dominance. Because autonomic balance may influence accommodation, the introversion of near-sighted and the extraversion of far-sighted persons may be related to the more general PNS-SNS balance rather than only to the difference in visual functioning. Research relevant to this hypothesis is reviewed.