THE EFFECT OF STIMULUS CONTRAST ON THE ACCOMMODATION RESPONSE

Abstract—Accommodation responses to stimuli of various contrasts at a vergence of—5.0 dioptres were measured with an objective infra‐red optometer. Both an edge and sinusoidal gratings were employed. The sinusoidal gratings were 1.67, 5.0 and 15.0 c deg‐1. The accommodation responses changed little as object contrast was reduced, until an accommodation response contrast threshold (ARCT) was reached; below this ARCT considerable accommodative error occurred. Intersubject variation in the ARCT was also noted. The ARCT for the 15.0 c deg‐1 grating was significantly higher than for the other two gratings. On two subjects accommodation responses to the 5.0 c deg‐1 grating were measured over a stimulus range of +0.5 to‐0.5 dioptres with three grating modulations of 2.7, 8.0 and 25%. The results indicated that no contrast dependence occurs in the near range but that contrast may be important as the system approaches the far‐point. The data further indicate the importance of intermediate spatial frequencies as accommodative stimuli.

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