title: Visual function and cortical organization in carriers of blue cone monochromacy.
abstract: Carriers of blue cone monochromacy have fewer cone photoreceptors than normal. Here we examine how this disruption at the level of the retina affects visual function and cortical organization in these individuals. Visual resolution and contrast sensitivity was measured at the preferred retinal locus of fixation and visual resolution was tested at two eccentric locations (2.5° and 8°) with spectacle correction only. Adaptive optics corrected resolution acuity and cone spacing were simultaneously measured at several locations within the central fovea with adaptive optics scanning laser ophthalmoscopy (AOSLO). Fixation stability was assessed by extracting eye motion data from AOSLO videos. Retinotopic mapping using fMRI was carried out to estimate the area of early cortical regions, including that of the foveal confluence. Without adaptive optics correction, BCM carriers appeared to have normal visual function, with normal contrast sensitivity and visual resolution, but with AO-correction, visual resolution was significantly worse than normal. This resolution deficit is not explained by cone loss alone and is suggestive of an associated loss of retinal ganglion cells. However, despite evidence suggesting a reduction in the number of retinal ganglion cells, retinotopic mapping showed no reduction in the cortical area of the foveal confluence. These results suggest that ganglion cell density may not govern the foveal overrepresentation in the cortex. We propose that it is not the number of afferents, but rather the content of the information relayed to the cortex from the retina across the visual field that governs cortical magnification, as under normal viewing conditions this information is similar in both BCM carriers and normal controls.
authors.affiliation: School of Optometry, University of California, Berkeley, Berkeley, California, United States of America. erossi@cvs.rochester.edu
authors.forename: Ethan A
authors.initials: EA
authors.lastname: Rossi
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Achtman
authors.forename: Arnaud
authors.initials: A
authors.lastname: Guidon
authors.forename: David R
authors.initials: DR
authors.lastname: Williams
authors.forename: Austin
authors.initials: A
authors.lastname: Roorda
authors.forename: Daphne
authors.initials: D
authors.lastname: Bavelier
authors.forename: Joseph
authors.initials: J
authors.lastname: Carroll
mesh_terms: D000328:Adult; D002452:Cell Count; D003116:Color; D003117:Color Vision Defects / Q000473:pathology* / Q000503:physiopathology*; D005260:Female; D005584:Fovea Centralis / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D012165:Retinal Ganglion Cells / Q000473:pathology; D014792:Visual Acuity; D014793:Visual Cortex / Q000473:pathology* / Q000503:physiopathology*