December 2019
Volume 19, Issue 15
Open Access
OSA Fall Vision Meeting Abstract  |   December 2019
The Spectral Drive Hypothesis of Emmetropization
Author Affiliations
  • Timothy J. Gawne
    Associate Professor, University of Alabama at Birmingham (UAB) Dept. Optometry and Vision Science, 1716 University Blvd. HPB 528, Birmingham AL. 35294, tgawne@uab.edu, tgawne@gmail.com, 205-934-5495 (phone)
Journal of Vision December 2019, Vol.19, 13. doi:https://doi.org/10.1167/19.15.13
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      Timothy J. Gawne; The Spectral Drive Hypothesis of Emmetropization. Journal of Vision 2019;19(15):13. doi: https://doi.org/10.1167/19.15.13.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

It is now well established that the post-natal developing eye uses optical cues to regulate its axial growth to achieve good focus, a process termed emmetropization. However, the visual cues that the eye uses have remained unclear. Here we present evidence that the primary visual cue is the sensing of different image statistics by the short-wavelength sensitive (SWS) and long-wavelength sensitive (LWS) cone photoreceptors, caused by longitudinal chromatic aberration. We use as a model system the tree shrew Tupaia glis belangeria, small diurnal dichromatic mammals closely related to primates. We develop an optical model for how the SWS and LWS photoreceptors represent an image at different levels of defocus and under different spectral lighting conditions. The model produces two values: a target, a point at which the image statistics of the SWS and LWS photoreceptors are in balance, and a drive, an imbalance in SWS and LWS image statistics which serves to direct eye growth towards the target in a sign-dependent manner. The model makes specific predictions for emmetropization under different spectral lighting conditions, which have been tested in juvenile tree shrews. Critically, while the purpose of emmetropization is to achieve good focus, it is not actually guided by focus, and it can ignore defocus cues if the spectral drive is artificially manipulated. The results may have implications for developing optical treatments to help reduce the growing worldwide burden of human myopia.

Footnotes
 Supported by NEI R21 EY025254 and NEI RO1 028578, and P30EY003909 (Core). The author acknowledges useful discussions with Dr. Thomas Norton, Dr. Rafael Grytz, and Dr. Tamara Oechslin, and the technical assistance of Russell Veale, Johanna Henry, and Eric Worthington.
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