The purpose of this study was to determine if accommodative responses to positive and negative contrast video displays differ significantly under two different levels of ambient illumination. The accommodative responses of 20 optometry students were measured (using a vernier Badal optometer) while characters on a video display terminal (VDT) were viewed binocularly under different screen and surround illumination conditions. Results showed no significant difference in accommodative response between negative and positive contrast VDT screens, but did reveal statistically significant differences (p < .05) for two levels of ambient illumination. For both negative and positive contrast conditions, the lower ambient level was associated with a decreased accommodative response (greater lag of accommodation).
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