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Norberto Lopez-Gil, Mateusz Tomasz Jaskulski, Fernando Vargas-Martin, Philip B Kruger; Retinal blood vessels may be used to detect the sign of defocus. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3958. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
We propose a new strategy that may permit the visual system to get objective information of the sign of defocus under monocular viewing conditions. It is based on the differences between the retinal images focused in front or behind the peripheral retina produced by the presence of a blood vessel network of arteries and veins in front of the photoreceptor layer.
We performed two types of studies: geometrical and diffractional retinal image simulations using ray tracing software (Optics Studio, Zemax®); and experimental measurements, using a camera with a fine printed irregular reticle of 25 microns, placed a few tenths of a millimeter in front a high resolution CCD. Two types of images were compared: with the image out of focus in front (myopic) or behind (hyperopic) the ideal image plane (photoreceptors or CCD layer).
Myopic and hyperopic retinal images of extended objects are different when the simulated blood vessel network or a real reticle is placed in front of the ideal image plane. These differences are not found in the absence of the vessels/reticle. Ray-tracing simulations and experimental images show that myopic images of extended objects formed close to the vessels/reticle plane present larger values of contrast at high spatial frequencies than the hyperopic or in focus images (figure). This effect is more evident when the spatial frequency of objects and vessels are similar. In particular, Fourier analysis of the experimental myopic and hyperopic images defocused approximately by the same amount, shows a different phase transfer function as well as a larger power spectrum magnitude (between 2.4 and 9 times larger at 12 c/deg) in the myopic image compared to the hyperopic one. This phenomenon can be explained by geometrical optics as it is due to different shadow and penumbra shapes originated by the vessels/reticle depending on the sign of defocus.
The retinal image formed through a blood vessel network contains information about the sign of defocus that may be used by the visual system as an objective cue for accommodation under monocular vision. The increase of higher spatial frequency content in the myopic image in the retinal periphery (where blood vessels are present) may play a role in the emmetropization process and inhibit myopia progression.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Letter chart images with a fine reticle in front the CCD.
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