Accommodation, convergence, and distance perception in low illumination.

The role of oculomotor adjustments for distance perception in dim light was investigated while preserving the natural interactions between accommodation and convergence. The results show that perceived distance in the dark is biased toward an intermediate value that is correlated with the vergence adjustment assumed in darkness but unrelated to the dark focus of accommodation. A subsequent experimient showed that short-term adaptation to base-out prisms and negative lenses of corresponding strength affects perceived distance and dark convergence but has no influence on the dark focus of accommodation. These findings were interpreted as indicating that convergence is a more important distance cue than accommodation under low illumination and that the physiological resting states of convergence and accommodation are relatively independent.