OBJECTIVE CONCURRENT MEASURES OF OPEN-LOOP ACCOMMODATION AND VERGENCEUNDER PHOTOPIC CONDITIONS

Purpose. To investigate the relationship between photopic open-loop ac commodation and vergence and the effect of mental effort on these posi tions. Methods. Twenty subjects (11 men and 9 women) viewed monocularl y a photopic (25 cdm-2), high-contrast (90%) Maltese cross-target for 3 minutes, through a 0.5-mm pinhole drilled into an infrared filter. A ccommodation was measured objectively at 1-second intervals using a Ca non Autoref R-1 infrared optometer, and vergence was recorded continuo usly and objectively using a differential infrared eye tracking system . Results. Under passive viewing conditions there was a significant co rrelation between photopic open-loop accommodation and vergence (R = 0 .671, P = 0.0012); for the majority of subjects the imposition of ment al effort shifted the passive levels of both open-loop accommodation a nd vergence, but these shifts were unsystematic and uncorrelated (R = 0.259, P = 0.270). The active open-loop positions of accommodation and vergence were also found to be correlated (R = 0.692, P = 0.0007). Co nclusions. The influence of proximal stimuli can explain the correlati ons identified between photopic open-loop positions of accommodation a nd vergence. The uncorrelated responses of the accommodation and verge nce systems to mental effort are likely to reflect interactions betwee n various spatiotopic stimuli including mental effort and perceived pr oximity.