Spectral bandwidth and ocular accommodation

Schnurmacher Institute for Vision Research, State College of Optometry, State University of New York, New York 10010.
Journal of the Optical Society of America A (Impact Factor: 1.56). 04/1995; 12(3):450-5. DOI: 10.1364/JOSAA.12.000450
Source: PubMed


Previous studies have suggested that targets illuminated by monochromatic (narrow-band) light are less effective in stimulating the eye to change its focus than are black-white (broadband) targets. The present study investigates the influence of target spectral bandwidth on the dynamic accommodation response in eight subjects. The fixation target was a 3.5-cycle/deg square-wave grating illuminated by midspectral light of various bandwidths [10, 40, and 80 nm and white (CIE Illuminant B)]. The target was moved sinusoidally toward and away from the eye, and accommodation responses were recorded and Fourier analyzed. Accommodative gain increases, and phase lag decreases, with increasing spectral bandwidth. Thus the eye focuses more accurately on targets of wider spectral bandwidth. The visual system appears to have the ability to analyze polychromatic blur to determine the state of focus of the eye for the purpose of guiding the accommodation response.

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Available from: Philip Kruger, Jun 02, 2014
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    • "Gain values would have been higher if a higher contrast stimulus had been used (Mathews & Kruger, 1989), but the contrast of the stimulus (27%) was limited by the physical capabilities of the display monitor. Gain also would have been higher with a closed loop stimulus for LCA (Aggarwala et al., 1995a, 1995b), since the gain for a dynamic accommodation response in white light is greater than the gain for a dynamic accommodation response in monochromatic light. Nevertheless, the variability in gain among subjects is a common Wnding in accommodation experiments. "
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    ABSTRACT: The accommodation response is sensitive to the chromatic properties of the stimulus, a sensitivity presumed to be related to making use of the longitudinal chromatic aberration of the eye to decode the sign of the defocus. Thus, the relative sensitivity to the long- (L) and middle-wavelength (M) cones may influence accommodation and may also be related to an individual's refractive error. Accommodation was measured continuously while subjects viewed a sine wave grating (2.2c/d) that had different cone contrast ratios. Seven conditions tested loci that form a circle with equal vector length (0.27) at 0, 22.5, 45, 67.5, 90, 120, 145 deg. An eighth condition produced an empty field stimulus (CIE (x,y) co-ordinates (0.4554, 0.3835)). Each of the gratings moved at 0.2 Hz sinusoidally between 1.00 D and 3.00 D for 40s, while the effects of longitudinal chromatic aberration were neutralized with an achromatizing lens. Both the mean level of accommodation and the gain of the accommodative response, to sinusoidal movements of the stimulus, depended on the relative L and M cone sensitivity: Individuals more sensitive to L-cone stimulation showed a higher level of accommodation (p=0.01; F=12.05; ANOVA) and dynamic gain was higher for gratings with relatively more L-cone contrast. Refractive error showed a similar correlation: More myopic individuals showed a higher mean level of accommodation (p<0.01; F=11.42; ANOVA) and showed higher gain for gratings with relatively more L-cone than M-cone contrast (p=0.01; F=10.83 ANOVA). If luminance contrast is maximized by accommodation, long wavelengths will be imaged behind the photoreceptors. Individuals in whom luminance is dominated by L-cones may maximize luminance contrast both by accommodating more, as shown here, and by increased ocular elongation, resulting in myopia, possibly explaining the correlations reported here among relative L/M-cone sensitivity, refractive error and accommodation.
    Full-text · Article · Oct 2006 · Vision Research
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    • "In support of S-cone involvement, several experiments have demonstrated an accommodation response to targets illuminated by short wavelength light (Van der Wildt et al., 1974; Charman & Tucker, 1978; Kergoat & Lovasik, 1990). In addition, an increased response was observed when the spectral bandwidth of the illumination was broadened to include short wavelength light (Aggarwala et al., 1995a). However, these experiments did not attempt to isolate the S-cone response , and the accommodation response may have been the result of the L-or M-cone contribution at short-wavelengths. "
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    ABSTRACT: Both long- and middle-wavelength sensitive cones mediate the reflex accommodation signal but the contribution from the short-wavelength sensitive cones is unknown. A short-wavelength sensitive cone contribution could extend the range of the signed defocus signal from chromatic aberration. The aim was to determine whether isolated short-wavelength sensitive cones mediate reflex accommodation independently of long- and middle-wavelength sensitive cones. Accommodation was monitored continuously (eight subjects) to a sine-wave grating (3 cpd; 0.53 contrast) moving with a sum of sines motion in a Badal optometer. Two illumination conditions were used: a 'blue' condition that isolated short-wavelength sensitive cones, and a 'white' control condition that stimulated all three cone types. Of the eight subjects, two responded equally in the 'white' and 'blue' condition, four gave reduced responses in the 'blue' condition and two failed to respond in both conditions. The mean response in the 'blue' condition was reduced by 50% compared to the 'white' condition. Further analysis indicated that four of the eight subjects gave responses that were considerably greater than noise (S.D.>1.82) when short-wavelength sensitive cones were isolated. Some subjects can accommodate using only S-cones.
    Full-text · Article · Apr 2001 · Vision Research
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    • "When viewing targets presented in optical systems, many subjects have poorer accommodation responses under reduced spectral bandwidth illumination (Kruger et al., 1993, 1997a; Aggarwala et al., 1995a,b), although some continue to focus normally (Charman and Tucker, 1978; Bobier et al., 1992; Kotulak et al., 1995; Kruger et al., 1997a). Thus, in natural viewing conditions there is the potential for poor accommodation in monochromatic (e.g., low pressure sodium) or reduced bandwidth light (e.g., high pressure sodium). "
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    ABSTRACT: The eye's longitudinal chromatic aberration (LCA) is known to drive 'reflex' accommodation to moving objects, but the evidence is not as clear for stationary objects. The present study examined whether accommodation can be driven by static simulations of the effects of defocus and LCA. Accommodation was recorded continuously while each of 12 subjects viewed images (through a 0.75 mm pinhole) that simulated the appearances of blurred sine wave gratings (3.9 c.p.d.). In two experimental conditions, an eye with normal LCA was assumed and defocus of +1 D or -1 D was simulated. In a control condition, an eye with neutralised LCA was assumed and target defocus of 1 D was simulated. Subjects' accommodation responses were consistent with the hypothesis that LCA provides a stimulus to accommodation. Chromatic aberration drives accommodation to both moving and stationary objects, and thus is an important stimulus for accommodation in everyday situations. The study findings are discussed in relation to colour vision, visual display terminals and emmetropization.
    Full-text · Article · Jun 1999 · Ophthalmic and Physiological Optics
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