Early Processing of Foveal Vision

Organizers: Lisa Ostrin1, David Brainard2, Lynne Kiorpes3; 1University of Houston College of Optometry, 2University of Pennsylvania, 3New York University
Presenters: Susana Marcos, Brian Vohnsen, Ann Elsner, Juliette E. McGregor

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This year’s biennial ARVO at VSS symposium focuses on early stages of visual processing at the fovea. Speakers will present recent work related to optical, vascular, and neural factors contributing to vision, as assessed with advanced imaging techniques. The work presented in this session encompasses clinical and translational research topics, and speakers will discuss normal and diseased conditions.


Foveal aberrations and the impact on vision

Susana Marcos1; 1Institute of Optics, CSIC

Optical aberrations degrade the quality of images projected on the retina. The magnitude and orientation of the optical aberrations vary dramatically across individuals. Changes also occur with processes such as accommodation, and aging, and also with corneal and lens disease and surgery. Certain corrections such as multifocal lenses for presbyopia modify the aberration pattern to create simultaneous vision or extended depth-of-focus. Ocular aberrometers have made their way into the clinical practice. Besides, quantitative 3-D anterior segment imaging has allowed quantifying the morphology and alignment of the cornea and lens, linking ocular geometry and aberrations through custom eye models, and shedding light on the factors contributing to the optical degradation. However, perceived vision is affected by the eye’s aberrations in more ways than those purely predicted by optics, as the eye appears to be adapted to the magnitude and orientation of its own optical blur. Studies using Adaptive Optics, not only reveal the impact of manipulating the optical aberrations on vision, but also that the neural code for blur is driven by subject’s own aberrations.

The integrated Stiles-Crawford effect: understanding the role of pupil size and outer-segment length in foveal vision

Brian Vohnsen1; 1Advanced Optical Imaging Group, School of Physics, University College Dublin, Ireland

The Stiles-Crawford effect of the first kind (SCE-I) describes a psychophysical change in perceived brightness related to the angle of incidence of a ray of light onto the retina. The effect is commonly explained as being due to angular-dependent waveguiding by foveal cones, yet the SCE-I is largely absent from similar-shaped rods suggesting that a different mechanism than waveguiding is at play. To examine this, we have devised a flickering pupil method that directly measures the integrated SCE-I for normal pupil sizes in normal vision rather than relying on mathematical integration of the standard SCE-I function as determined with Maxwellian light. Our results show that the measured effective visibility for normal foveal vision is related to visual pigment density in the three-dimensional retina rather than waveguiding. We confirm the experimental findings with a numerical absorption model using Beer-Lambert’s law for the visual pigments.

Structure of cones and microvasculature in healthy and diseased eyes

Ann Elsner1; 1Indiana University School of Optometry

There are large differences in the distribution of cones in the living human retina, with the density at the fovea varying more than with greater eccentricities. The size and shape of the foveal avascular zone also varies across individuals, and distances between capillaries can be greatly enlarged in disease. While diseases such as age-related macular degeneration and diabetes impact greatly on both cones and retinal vessels, some cones can survive for decades although their distributions become more irregular. Surprisingly, in some diseased eyes, cone density at retinal locations outside those most compromised can exceed cone density for control subjects.

Imaging of calcium indicators in retinal ganglion cells for understanding foveal function

Juliette E. McGregor1; 1Centre for Visual Science, University of Rochester

The fovea mediates much of our conscious visual perception but is a delicate retinal structure that is difficult to investigate physiologically using traditional approaches. By expressing the calcium indicator protein GCaMP6s in retinal ganglion cells (RGCs) of the living primate we can optically read out foveal RGC activity in response to visual stimuli presented to the intact eye. Pairing this with adaptive optics ophthalmoscopy it is possible to both present highly stabilized visual stimuli to the fovea and read out retinal activity on a cellular scale in the living animal. This approach has allowed us to map the functional architecture of the fovea at the retinal level and to classify RGCs in vivo based on their responses to chromatic stimuli. Recently we have used this platform as a pre-clinical testbed to demonstrate successful restoration of foveal RGC responses following optogenetic therapy.

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