Factors influencing the dynamics of accommodative and pupillary responses in humans

Purpose. The aims of the research are to understand (1) the dynamics of the focusing responses from far-to-near (accommodation) and near-to-far (disaccommodation) over a wide range of amplitudes, (2) the influence of amplitude and starting point on the dynamics of accommodative and disaccommodative responses, (3) age related changes in the dynamics of accommodative and disaccommodative responses, (4) the static and dynamic characteristics of the pupil responses associated with accommodation and disaccommodation and (5) the age related changes in the static and dynamic characteristics of the near pupil response.;Methods. Dynamic accommodative and pupillary responses to step stimuli presented in real space were measured in human subjects with a PowerRefractor at 25 Hz. In experiments 1, 3, 4 & 5, various amplitude responses were stimulated by alternately presenting targets at a fixed far (6 meters) and various near distances corresponding to stimulus demands from 1 D to 6 D in 1 D steps. In experiment 2, the amplitude and starting point of the responses were manipulated by placing the targets at various far and near distances. The responses were fitted with analytical functions to calculate time constant and peak velocity. Experiments 1, 2 & 4 included young subjects in the age range 20 and 30 years and experiments 3 & 5 included subjects over a wide age range from 14 to 45 years.;Results. Experiment 1: Time constant of accommodation and peak velocity of disaccommodation increased linearly with amplitude. Disaccommodation was progressively faster than accommodation with increasing amplitudes. Experiment 2: Starting point exerted a greater influence than amplitude on the dynamics of accommodative and disaccommodative responses. Accommodative and disaccommodative responses were faster at proximal starting points than at distal starting points. Experiment 3: Speed of accommodation decreased with age, but not the speed of disaccommodation. Latency of accommodation did not change with age, but the latency of disaccommodation increased with age. Experiment 4: Amplitude of pupil responses increased linearly with the amplitude of accommodation and disaccommodation. Latency of accommodation was shorter than the associated pupil response. Time constants of pupil constriction increased linearly with the amplitude. Experiment 5: There was no increase in the magnitude of near pupil constriction with increasing age. Peak velocity of pupil constriction decreased with age.;Conclusions. The dynamics of accommodation, disaccommodation and pupillary responses are influenced by the biomechanics of the intraocular structures involved in producing these responses. The differences in the age related changes in the dynamics of accommodation and disaccommodation suggest that age related changes leading to presbyopia mostly occur in the crystalline lens and capsule. The lack of change in the magnitude of near pupil response with age suggests that there is no increase in the near effort with the progression of presbyopia.