The effect of stimulus contrast on the accommodation response.
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.
Ward
P A
PA
Department of Ophthalmic Optics, UMIST, Manchester, U.K.
D000065:Accommodation, Ocular; D000328:Adult; D005260:Female; D006801:Humans; D008027:Light; D008297:Male; D010775:Photic Stimulation; D012684:Sensory Thresholds