Spatiotopic cues enhance the dynamic accommodation response profile

Abstract

Purpose: To determine the influence of optically-induced and real changes in stimulus vergence on the profile of the accommodation response. Method: Accommodation was measured on 8 visually normal subjects (mean age 25.6±6.0 years) using a dynamic tracking infra-red optometer. A Badal stimulus optometer was used to induce optical changes in stimulus vergence which eliminated spatiotopic cues. Targets were also located in real space to provide both retinotopic and spatiotopic cues. Step changes in stimulus vergence were modulated over a 2 D (2–4 D) range for both conditions. Data were collected at a sampling rate of 102.4 Hz using a digital storage oscilloscope which was interfaced to an IBM PC. Results: Mean responses are presented below. An ANOVA revealed no significant difference between overall response times to optically-induced and real changes in stimulus vergence although the response profiles were different between conditions. Conclusions: Spatiotopic cues enhance the accommodation response profile for step changes in stimulus vergence by reducing initial directional error and ensuring the magnitude of the response is appropriate to the stimulus demand. However, overall response times were found to be similar under both viewing conditions.