Dynamics of the Pupillary Near Response

Abstract

Abstract: : Purpose: Accommodation results in an associated pupil constriction. The dynamics of this pupillary near response are not well understood. In this study, the static and dynamic aspects of the pupillary response during accommodation and disaccommodation are explored. Methods: Accommodative and pupillary responses to 10–15 cycles of step stimulus demands from 1D to 7D in 1D steps were measured simultaneously using a video–based optometer (PowerRefractor) at 25 Hz in 6 subjects (ages: 23 – 26 yrs). ‘Star’ like stimuli were presented at far and near distances, illuminated alternately with ultra bright white LEDs. The near and far targets were matched in luminance (10 cd/m² background) but not in angular subtense. Software was used to objectively determine the linear portion of the accommodative and disaccommodative responses, i.e. the data after latency and before steady state. From this data, the change in pupil diameter with accommodation and the velocity of the pupillary near response were calculated. Results: Changes in pupil diameter were linearly related to accommodation (p < 0.05) and disaccommodation (p < 0.05). The slope of the relationship was different between accommodation (slope = 0.36 mm/D) and disaccommodation (slope = 0.11 mm/D) (p < 0.05). The rate of pupil change (mm/D) did not change systematically with amplitude of accommodation (r² = 0.01) or disaccommodation (r² = 0.07). Velocity of accommodative and disaccommodative pupil responses increased linearly with amplitude of the pupil response (p < 0.05 in each case). The relationship between pupil response velocity and amplitude was not different between accommodation and disaccommodation (F_(2,541) = 0.002, p = 0.99). Conclusions: A greater pupil constriction occurs with accommodation than dilation occurs with disaccommodation. Qualitatively, the pupil constricted with accommodation and began dilating while accommodation was maintained, resulting in a reduced pupil change with disaccommodation. The relationship between velocity and extent of the pupil response are similar for accommodation and disaccommodation, although the extent of pupil response is greater for accommodation than for disaccommodation.

Keywords: pupillary reflex • ocular motor control • refraction