An opponent dual-detector spectral drive model of emmetropization. (August 2020)

• Record Type: Journal Article
• Authors: Gawne, Timothy J.; Norton, Thomas T.
• Is Part Of: Vision research. Volume 173(2020)
• Page Start: 7
• Page End: 20
• Publication Date: 2020-08
• Subjects: Emmetropization -- Myopia -- Focus -- Blur -- Spatial frequency -- Chromatic aberrations -- Image statistics; Vision -- Periodicals; 573.88
• DOI: 10.1016/j.visres.2020.03.011
• Languages: English
• ISSNs: 0042-6989

Abstract

Graphical abstract: Highlights: A model is proposed whereby longitudinal chromatic aberration guides emmetropization. Effects of defocus on arrays of long- and short-wavelength cones are described. The eye is guided to a point of balance of image contrast in both cone arrays. Sparse spacing of short-wavelength cones is not in principle a limiting factor. Abstract: In post-natal developing eyes a feedback mechanism uses optical cues to regulate axial growth so as to achieve good focus, a process termed emmetropization. However, the optical cues that the feedback mechanism uses have remained unclear. Here we present evidence that a primary visual cue may be the detection of different image statistics by the short-wavelength sensitive (SWS) and long-wavelength sensitive (LWS) cone photoreceptors, caused by longitudinal chromatic aberration (LCA). We use as a model system the northern tree shrew Tupaia belangeri, diurnal cone-dominated dichromatic mammals closely related to primates. We present an optical model in which the SWS and LWS photoreceptors each represent an image at different levels of defocus. The model posits that an imbalance between SWS and LWS image statistics directs eye growth towards the point at which these image statistics are in balance. Under spectrally broadband ("white") lighting, the focus of the eye is driven to a target point approximately in the middle of the visible spectrum, which is emmetropia. Calculations suggest that the SWS cone array, despite the sparse number of SWS cones, can plausibly detect the wavelength-dependent differences in defocus and guide refractive development. The model is consistent with the effects of various narrow-band illuminants on emmetropization in tree shrews. Simulations suggest that common artificial light spectra do not interfere with emmetropization. Simulations also suggest that multi-spectral multi-focal lenses, where the different optical zones of a multifocal lens have different spectral filtering properties, could be an anti-myopia intervention.