Mean response and oscillations of accommodation with colour and contrast.

The mean level and microfluctuations of accommodation were objectively recorded, in natural viewing conditions, by infrared optometry on steady presentation of various combinations of achromatic and coloured Snellen E on achromatic or coloured fields, with or without a luminance contrast. In addition to the absolute mean power spectrum of the microfluctuations, the HF/LF ratio of the high (HF, 0.5-6 Hz) and low (LF, 0-0.5 Hz) frequency activity of this phenomenon, which provides a sensitive objective description of the control, was analysed. In the case of maximum luminance contrast, for any monochrome situation, the HF/LF ratio decreases when changing from an achromatic-only contrast to a saturated coloured situation. At the same time, the relative shifts of the mean level of accommodation, which compensate ocular chromatism under coloured conditions, increase with colour saturation. In the case of an isoluminant chromatic contrast, the decrease in the HF/LF ratio was significant. This result confirms the inefficiency of chromatic contrast to control accommodation. Furthermore, this study confirms that both LF and HF absolute activity of the microfluctuations of accommodation are usually related to the stimulus characteristics. Their antagonistic behaviour is an argument for considering the HF/LF ratio.