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Visual function and cortical organization in carriers of blue cone monochromacy.

Rossi EA, Achtman RL, Guidon A, Williams DR, Roorda A, Bavelier D, Carroll J - PLoS ONE (2013)

Bottom Line: Retinotopic mapping using fMRI was carried out to estimate the area of early cortical regions, including that of the foveal confluence.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.

View Article: PubMed Central - PubMed

Affiliation: School of Optometry, University of California, Berkeley, Berkeley, California, United States of America. erossi@cvs.rochester.edu

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.

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Fixation stability.a) BCM carriers with substantial cone loss had unstable fixation when compared to normal controls. SD of stimulus position averaged for vertical and horizontal directions as a function of eccentricity. Solid and dashed lines are linear regression line and upper and lower 95% confidence intervals fit to data from 6 normal eyes (control eye and 5 normal eyes from Rossi & Roorda, 2010). JC_1043, JC_1041, JC_1045 (OD), JC_1045 (OS) are shown as green triangles, red diamonds, dark blue, and light blue squares, respectively. Control eye is shown as a black X. JC_1041, JC_1045 fell outside the normal range at all locations, while JC_1043 (the carrier with the least amount of cone loss) and the control eye both fell within the normal range at all test locations. b) BCM carriers and normal controls where more stable when looking at the stimulus vs. the fixation target. Normal observers (white bars) are more stable than carriers (blue bars) in either condition. Mean of 6 normal eyes is shown (the control eye, and the 5 normal eyes from Rossi & Roorda, 2010). Mean of the 4 carrier eyes in (a) are shown. Error bars are ± SEM.
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pone-0057956-g008: Fixation stability.a) BCM carriers with substantial cone loss had unstable fixation when compared to normal controls. SD of stimulus position averaged for vertical and horizontal directions as a function of eccentricity. Solid and dashed lines are linear regression line and upper and lower 95% confidence intervals fit to data from 6 normal eyes (control eye and 5 normal eyes from Rossi & Roorda, 2010). JC_1043, JC_1041, JC_1045 (OD), JC_1045 (OS) are shown as green triangles, red diamonds, dark blue, and light blue squares, respectively. Control eye is shown as a black X. JC_1041, JC_1045 fell outside the normal range at all locations, while JC_1043 (the carrier with the least amount of cone loss) and the control eye both fell within the normal range at all test locations. b) BCM carriers and normal controls where more stable when looking at the stimulus vs. the fixation target. Normal observers (white bars) are more stable than carriers (blue bars) in either condition. Mean of 6 normal eyes is shown (the control eye, and the 5 normal eyes from Rossi & Roorda, 2010). Mean of the 4 carrier eyes in (a) are shown. Error bars are ± SEM.

Mentions: Fixation stability was assessed by precisely localizing the position of the stimulus on the retina for each frame of the AOSLO video from each psychophysical trial. This positional information precisely localized test locations for comparing MARAO and Nc and had the further advantage of providing a trace of eye position for assessing fixation stability. The standard deviation of the position of the stimulus on the retina at each psychophysics test location is a precise measurement of the fixational spread of the eye. The standard deviation of the stimulus position (averaged for both x and y directions) is plotted versus eccentricity in Figure 8a. For comparison, a linear regression fit, with upper and lower 95% confidence intervals is plotted for 6 normal observers (the 5 eyes from [31] and the control eye from this study). Two of the BCM carriers (JC_1041 and JC_1045) had fixational eye movements that were outside the normal range at all locations, while one (JC_1043) was within the normal limits at all test locations. Figure 8b compares the SD of eye position when observers either looked at the fixation target or at the stimulus. Fixation was more stable for both groups when looking at the stimulus than when looking at the fixation target, with the carriers showing less stable fixation than normal observers in both conditions.


Visual function and cortical organization in carriers of blue cone monochromacy.

Rossi EA, Achtman RL, Guidon A, Williams DR, Roorda A, Bavelier D, Carroll J - PLoS ONE (2013)

Fixation stability.a) BCM carriers with substantial cone loss had unstable fixation when compared to normal controls. SD of stimulus position averaged for vertical and horizontal directions as a function of eccentricity. Solid and dashed lines are linear regression line and upper and lower 95% confidence intervals fit to data from 6 normal eyes (control eye and 5 normal eyes from Rossi & Roorda, 2010). JC_1043, JC_1041, JC_1045 (OD), JC_1045 (OS) are shown as green triangles, red diamonds, dark blue, and light blue squares, respectively. Control eye is shown as a black X. JC_1041, JC_1045 fell outside the normal range at all locations, while JC_1043 (the carrier with the least amount of cone loss) and the control eye both fell within the normal range at all test locations. b) BCM carriers and normal controls where more stable when looking at the stimulus vs. the fixation target. Normal observers (white bars) are more stable than carriers (blue bars) in either condition. Mean of 6 normal eyes is shown (the control eye, and the 5 normal eyes from Rossi & Roorda, 2010). Mean of the 4 carrier eyes in (a) are shown. Error bars are ± SEM.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3585243&req=5

pone-0057956-g008: Fixation stability.a) BCM carriers with substantial cone loss had unstable fixation when compared to normal controls. SD of stimulus position averaged for vertical and horizontal directions as a function of eccentricity. Solid and dashed lines are linear regression line and upper and lower 95% confidence intervals fit to data from 6 normal eyes (control eye and 5 normal eyes from Rossi & Roorda, 2010). JC_1043, JC_1041, JC_1045 (OD), JC_1045 (OS) are shown as green triangles, red diamonds, dark blue, and light blue squares, respectively. Control eye is shown as a black X. JC_1041, JC_1045 fell outside the normal range at all locations, while JC_1043 (the carrier with the least amount of cone loss) and the control eye both fell within the normal range at all test locations. b) BCM carriers and normal controls where more stable when looking at the stimulus vs. the fixation target. Normal observers (white bars) are more stable than carriers (blue bars) in either condition. Mean of 6 normal eyes is shown (the control eye, and the 5 normal eyes from Rossi & Roorda, 2010). Mean of the 4 carrier eyes in (a) are shown. Error bars are ± SEM.
Mentions: Fixation stability was assessed by precisely localizing the position of the stimulus on the retina for each frame of the AOSLO video from each psychophysical trial. This positional information precisely localized test locations for comparing MARAO and Nc and had the further advantage of providing a trace of eye position for assessing fixation stability. The standard deviation of the position of the stimulus on the retina at each psychophysics test location is a precise measurement of the fixational spread of the eye. The standard deviation of the stimulus position (averaged for both x and y directions) is plotted versus eccentricity in Figure 8a. For comparison, a linear regression fit, with upper and lower 95% confidence intervals is plotted for 6 normal observers (the 5 eyes from [31] and the control eye from this study). Two of the BCM carriers (JC_1041 and JC_1045) had fixational eye movements that were outside the normal range at all locations, while one (JC_1043) was within the normal limits at all test locations. Figure 8b compares the SD of eye position when observers either looked at the fixation target or at the stimulus. Fixation was more stable for both groups when looking at the stimulus than when looking at the fixation target, with the carriers showing less stable fixation than normal observers in both conditions.

Bottom Line: Retinotopic mapping using fMRI was carried out to estimate the area of early cortical regions, including that of the foveal confluence.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.

View Article: PubMed Central - PubMed

Affiliation: School of Optometry, University of California, Berkeley, Berkeley, California, United States of America. erossi@cvs.rochester.edu

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.

Show MeSH
Related in: MedlinePlus