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Nathan Doble, Rebecca Kivlin, Johanan Codona, Simone Li, Stacey Choi; Photoreceptor Pointing as a Function of Retinal Eccentricity in Normal Human Eyes. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3428.
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The optical alignment of the cone photoreceptors with respect to the pupil center is a potential metric to assess retinal health. Roorda and Williams (JOV, 2002) first made measurements of the directionality of single cone photoreceptors in normal human eyes. Choi et al, (IOVS 2008) subsequently performed measurements on a subject with retinal disease. We present work on a larger number of normal subjects at several retinal eccentricities.
The adaptive optics (AO) fundus camera at the New England College of Optometry was used to acquire retinal images on three normal human subjects, N1, N2 and N3 (ages 23 to 26) at 2 and 4 degrees in the nasal retina. 2 degrees temporal eccentricity was also measured in two of the subjects. At each location, a series of 1° diameter retinal images (680nm light) were acquired for 9 different entrance pupil positions. Images were then registered and a centroiding algorithm applied to determine the alignment property of individual cones at the pupil plane of the eye.
After processing, the pointing of approximately 600 cones at each retinal location could be measured. As an example, for subject N1, the projection of the cone pointing at the pupil plane from all retinal locations fell within an area of 0.25mm in diameter, located slightly nasally (0.15mm) from the pupil center along the horizontal meridian. The other subjects showed similar nasal bias in alignment with respect to the pupil center. Our disarray is smaller than that reported by previous studies (Roorda, JOV, 2002) possibly due to choosing areas that did not include retinal blood vessels.
For normal subjects, our results are in agreement with previous reports (both psychophysical and imaging studies) that the disarray of the photoreceptors is very small; which is to optimize the efficiency of light capture within the photoreceptors. In diseased eyes, larger variations in cone disarray were reported (Choi et al, IOVS 2008).
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