Purpose: Most current ophthalmic instruments operate monocularly and with a restricted field of view. However, many visual optics experiments should be performed binocularly and under natural viewing conditions. We have developed a new binocular optical sensor operating in real time with an open-view field measuring different optical parameters while subjects perform visual tasks.
Methods: The apparatus measure refraction, aberrations, pupil diameter and relative position on both eyes simultaneously with an invisible infrared (1050nm) beam while the subject unobtrusively observes the visual world. It consists of a single Hartmann-Shack wavefront sensor conjugated with both eyes’ pupil plane through twin periscopes. A dichroic mirror transmits the visible light allowing open-view to the subject while the infrared beams are reflected toward the sensor positioned in a lower plane. From the recorded images, both eye’s wave-aberrations, pupil size and relative convergence were measured in real time (25 Hz). The instrument was successfully applied in four normal subjects in an experiment where they were instructed to switch fixation between visual stimuli at 3 m and 30 cm nearly in the same line of sight. The task was performed binocularly and with a stop blocking the view for one eye.
Results: Dynamic changes in the accommodation response and convergence were consistent with the distances to the stimuli. Changes in pupil diameter and higher order aberrations were also recorded for different visual conditions. The temporal dynamics of these parameters when the subject switched targets showed a different behavior when both eyes were in use or one of them was blocked. Binocular accommodation response is faster than monocular one. Convergence was faster than the accommodation response in binocular conditions, but both events were roughly synchronized for monocular vision.
Conclusions: A new instrument for the non-invasive measurements of relevant optical parameters in both eyes simultaneously has been demonstrated. As an example of application, we have used the system to explore the dynamic relationship between accommodation and convergence. The instrument could be used to control the eyes’ optical properties in a wide range of realistic visual environments.