The influence of long-term visual near-work on accommodation and vergence: a field study.

A study of the influence of sustained, visual near-work upon a set of oculomotor functions (ZCSV i.e. Zone of Clear Single Vision) was carried out on a randomly drawn group (N = 43) of young, female, healthy and experienced accountants (mean age 24.6 years) who were daily engaged in full-time interactive VDT work. PRA (Positive Relative Accommodation), NRA (Negative Relative Accommodation), PRC (Positive Relative Convergence) and NRC (Negative Relative Convergence) was measured twice: 1) in the morning before the subjects started work and 2) at the end of the working day. Results showed significant reductions in the four ZCSV components over the working day. Vergence reductions accounted for over 60% of the ZCSV changes.