title: Photopigment optical density of the human foveola and a paradoxical senescent increase outside the fovea.
abstract: Photopigment optical density (OD) of middle-(M) and long-(L) wavelength-sensitive cones was determined to evaluate the hypothesis that reductions in the amount of photopigment are responsible for age-dependent sensitivity losses of the human cone pathways. Flicker thresholds were measured at the peak and tail of the photoreceptor's absorption spectrum as a function of the intensity of a bleaching background. Photopigment OD was measured at 0 (fovea), 2, 4, and 8 deg in the temporal retina by use of a 0.3-deg-diameter test spot. Seventy-two genetically characterized dichromats were studied so that the L- and M-cones could be analyzed separately. Subjects included 28 protanopes with M- but no L-cones and 44 deuteranopes with L- but no M-cones (all male, age range 12-29 and 55-83 years). Previous methods have not provided estimates of photopigment OD for separate cone classes in the foveola. In this study, it was found that foveolar cones are remarkably efficient, absorbing 78% of the available photons (OD = 0.65). Photopigment OD decreased exponentially with retinal eccentricity independently of age and cone type. Paradoxically, the OD of perifoveal cones increased significantly with age. Over the 70-year age range of our participants, the perifoveal M- and L-cones showed a 14% increase in capacity to absorb photons despite a 30% decrease in visual sensitivity over the same period.
authors.affiliation: Department of Ophthalmology and Section of Neurobiology, Physiology and Behavior, University of California, Davis, Sacramento, CA 95817, USA.
authors.forename: Agnes B
authors.initials: AB
authors.lastname: Renner
authors.forename: Holger
authors.initials: H
authors.lastname: Knau
authors.forename: Maureen
authors.initials: M
authors.lastname: Neitz
authors.forename: Jay
authors.initials: J
authors.lastname: Neitz
authors.forename: John S
authors.initials: JS
authors.lastname: Werner
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism*; D002648:Child; D003117:Color Vision Defects / Q000235:genetics / Q000378:metabolism*; D005584:Fovea Centralis / Q000378:metabolism*; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D012168:Retinal Pigments / Q000378:metabolism*
chemical_list: D012168:Retinal Pigments
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