The role of luminance and chromatic cues in emmetropisation

Abstract

Citation information: Rucker FJ. The role of luminance and chromatic cues in emmetropisation. Ophthalmic Physiol Opt 2013, 33, 196- Abstract Purpose: At birth most, but not all eyes, are hyperopic. Over the course of the first few years of life the refraction gradually becomes close to zero through a process called emmetropisation. This process is not thought to require accommodation, though a lag of accommodation has been implicated in myopia development, suggesting that the accuracy of accommodation is an important factor. This review will cover research on accommodation and emmetropisation that relates to the ability of the eye to use colour and luminance cues to guide the responses. Recent Findings: There are three ways in which changes in luminance and colour contrast could provide cues: (1) The eye could maximize luminance contrast. Monochromatic light experiments have shown that the human eye can accommodate and animal eyes can emmetropise using changes in luminance contrast alone. However, by reducing the effectiveness of luminance cues in monochromatic and white light by introducing astigmatism, or by reducing light intensity, investigators have revealed that the eye also uses colour cues in emmetropisation. (2) The eye could compare relative cone contrast to derive the sign of defocus information from colour cues. Experiments involving simulations of the retinal image with defocus have shown that relative cone contrast can provide colour cues for defocus in accommodation and emmetropisation. In the myopic simulation the contrast of the red component of a sinusoidal grating was higher than that of the green and blue component and this caused relaxation of accommodation and reduced eye growth. In the hyperopic simulation the contrast of the blue component was higher than that of the green and red components and this caused increased accommodation and increased eye growth. (3) The eye could compare the change in luminance and colour contrast as the eye changes focus. An experiment has shown that changes in colour or luminance contrast can provide cues for defocus in emmetropisation. When the eye is exposed to colour flicker the eye grows almost twice as much, and becomes more myopic, compared to when the eye is exposed to luminance flicker. Summary: Neural responses of the luminance and colour mechanisms direct accommodation and emmetropisation mechanisms to different focal planes. Therefore, it is likely that the set point of refraction and accommodation is dependent on the sensitivity of the eye to changes in spatial and temporal, colour and luminance contrast.

The wavelength composition and temporal modulation of ambient lighting strongly affect refractive development in young tree shrews

“…There have been a significant number of studies examining the effects of temporally and chromatically modulated ambient light on emmetropization (Britton et al, 2013; Crewther and Crewther, 2002; Crewther et al, 2006; Kee et al, 2007; Liu et al, 2014; Liu et al, 2011; Rohrer et al, 1995; Rucker et al, 2015; Rucker, 2013; Rucker and Wallman, 2012; Schwahn and Schaeffel, 1997; Yu et al, 2011), however the results have differed across labs, making them difficult to interpret. Some of this may be due to species differences between chicks, rodents, and primates/near primates, complicated by interactions between the specific wavelengths employed, the number of cones types, and their absorption peaks.…”

Opposing effects of atropine and timolol on the color and luminance emmetropization mechanisms in chicks

“…The differences in focus of the different wavelengths produce changes in color of the retinal image with defocus (16) , which in turn is reflected in changes in the stimulation of the retinal cones and the retinotectal color and luminance pathways (review: (19) ). A theoretical analysis of the change in the retinal image with defocus has indicated that with myopic defocus, the retina would experience changes in luminance contrast, whereas with hyperopic defocus the retina would also experience changes in color contrast (17) .…”

Lack of oblique astigmatism in the chicken eye

“…There were numerous attempts to identify visual cues that provide the retina with information about the sign of defocus. Longitudinal chromatic aberration was extensively studied (Schaeffel & Howland, 1991;Wildsoet et al, 1993), but it is clear that chromatic cues are at least not obligatory although they may interact with emmetropization (Rucker, 2013;Rucker & Wallman, 2009, 2012. Higher order aberrations could provide a sign of defocus-related cues (Wilson, Decker, & Roorda, 2002) but there is no convincing evidence that they are used during emmetropization (Wallman & Winawer, 2004).…”