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Elise W. Dees, Jungtae Rha, Alfredo Dubra, Rigmor C. Baraas; Variability In Parafoveal Cone Density In Normal Trichromatic Females. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3200.
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© ARVO (1962-2015); The Authors (2016-present)
Parafoveal function is important for daily visual tasks such as reading. Here we investigate the variability in cone density along the horizontal and vertical meridians in parafoveal regions of the retina in a group of healthy normal trichromatic females using adaptive optics retinal imaging.
The fovea and parafovea (0.5 to 3 deg eccentricity) of the dominant eye were imaged in 6 normal trichromatic females (20-30 yrs) with axial lengths (AL) from 21.43 to 25.75 mm and best-corrected logMAR acuity 0.00 to -0.08. The subject’s eye was dilated and accommodation suspended with Cyclopentolate 1 % prior to imaging. High-resolution images of the cone mosaic were obtained with the Kongsberg Adaptive Optics Ophthalmoscope (AOO). The AOO employs 780 nm and 840 nm super luminescent diodes (SLD; Superlum, Ltd., Ireland) as light sources for the wavefront sensing and imaging channels respectively. The imaging source is used in conjunction with a step-index multimode fiber (Fiberguide Industries, NJ, USA) to reduce speckle noise. AO correction was performed over a 6.8 mm diameter pupil with a Mirao52 (Image Eyes, France) deformable mirror and a custom-built Shack-Hartmann wavefront sensor. Images of the photoreceptor mosaic were collected with a 12-bit CCD camera (Cam1M100-SFT, Sarnoff Corporation, NJ, USA) at 167 fps with 6 ms exposure time. Individual cones were identified via automated and manual methods in images produced from averaged co-registered frames. Angular cone density was estimated after correcting image scaling for individual AL (IOLMaster, Carl Zeiss, Germany).
Cone density ranged from 34 000 to 51 000 cones/mm2 at 1° horizontally, and from 28 000 to 45 000 cones/mm2 vertically. Cone density declined by 25-30% per degree in both meridians. Between-individual variability ranged from 5 to 40% at 1° and 2°, and 5 to 25% at 3°. This results in an estimated difference in cone spacing of >25% and 20-25% respectively. Cone density was independent of AL between 1.0-3.0°, but increased with decreasing AL around 0.5° in both meridians.
The results are mostly in keeping with those of Curcio et al. (1990)1. Between-individual variability, however, is twice of what they reported at 1°. This suggests that between-individual variability in cone density and subsequent cone spacing may have a consequence for parafoveal visual function.1Curcio, et al., J Comp Neurol, 292: 497-523, 1990.
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