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Lucia Ziccardi, Giuseppe Lombardo, Vincenzo Parisi, Sebastiano Serrao, Marco Lombardo; Parafoveal cone metrics and their relationship with multifocal electroretinogram. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2620. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate density of parafoveal cones and the relative retinal bioelectrical responses assessed by multifocal electroretinogram (mfERG) across healthy population.
A flood-illumination adaptive optics (AO) retinal camera was used to obtain images of the parafoveal cone mosaic in 16 healthy volunteers (age ranging from 20 to 45 years and manifest refraction ranging from 0 to -6.25 diopters). Density and preferred packing arrangement of cones were estimated in 160x160 µm sampling areas along the horizontal and vertical meridians at 1.5 degrees eccentricity from the fovea. Additionally, subjects underwent to mfERG recording. MfERG ring analysis was performed to measure the response amplitude density (RAD) of the N1-P1 components (N1-P1 RAD, nV/deg2) and the P1 implicit time (P1 IT, ms) of the first-order binary kernels of the central ring (R1= 0-2.5° foveal eccentricity) for an adequate comparison with cone metrics. The Pearson coefficient was calculated in order to assess the correlation between cone metrics and retinal bioelectrical values. A multiple regression analysis was used to determine the weighted influence of demographic factors (age, manifest refraction) and functional variables on cone density.
Cone density tended to decline with aging (r=-0.49, P<0.05) and increased myopia (r=-0.55, P<0.05). Density was 9% higher (P<0.001) along the horizontal (30359 cones/mm2) than the vertical (28063 cones/mm2) meridian, while the mean percentage of hexagonal arrangement was 4% higher (P<0.01) along the vertical (49%) than the horizontal (45%) meridian. No correlation was found between cone metrics and R1 mfERG N1-P1 RAD and P1 IT values.
Although age and myopia were the most important demographic factors to influence density variation of parafoveal cones, the relative photoreceptors and off-bipolar cell function did not vary across a sample healthy population. Thereby, it is important to cluster subjects by age and manifest refraction in order to facilitate comparison between studies whose aim is to correlate cone metrics and retinal function.
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