Limits...
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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The Nyquist limit of the cone mosaic and adaptive optics corrected visual resolution.a) Nyquist limit of the cone mosaic (Nc) as a function of eccentricity. Lines colored after symbols in inset legend. The black X is the estimate of Nc converted from density of control eye measured in a previous study (Putnam et al., 2005). Dotted magenta line shows mean Nc derived from mean of densities reported by Curcio et al. (1990b). Solid and dashed grey lines are mean and ±2 SD of 6 normal eyes (the control eye and the 5 eyes from Rossi & Roorda, 2010). b) Adaptive optics corrected visual resolution (MARAO) as a function of eccentricity. Minimum angle of resolution (MAR) is shown on left ordinate, while equivalent Snellen acuity is shown on the right. Symbol-subject relations are provided in inset legend. Solid and dashed lines are regression line and 95% confidence intervals fit to the data of 5 normal observers from Rossi & Roorda (2010).
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pone-0057956-g004: The Nyquist limit of the cone mosaic and adaptive optics corrected visual resolution.a) Nyquist limit of the cone mosaic (Nc) as a function of eccentricity. Lines colored after symbols in inset legend. The black X is the estimate of Nc converted from density of control eye measured in a previous study (Putnam et al., 2005). Dotted magenta line shows mean Nc derived from mean of densities reported by Curcio et al. (1990b). Solid and dashed grey lines are mean and ±2 SD of 6 normal eyes (the control eye and the 5 eyes from Rossi & Roorda, 2010). b) Adaptive optics corrected visual resolution (MARAO) as a function of eccentricity. Minimum angle of resolution (MAR) is shown on left ordinate, while equivalent Snellen acuity is shown on the right. Symbol-subject relations are provided in inset legend. Solid and dashed lines are regression line and 95% confidence intervals fit to the data of 5 normal observers from Rossi & Roorda (2010).

Mentions: Cone spacing at the PRLF was larger than normal in BCM carrier eyes. The average minimum ICD measured from the four carrier eyes was 0.79 arcmin (SD = 0.03). JC_1041 had the largest minimum ICD of 0.84 arcmin. JC_1045 had minimum ICD of 0.79 arcmin in each eye. JC_1043 had the lowest ICD, of 0.76 arcmin. Minimum ICD was found less than 3 arcmin from the PRLF for all carrier eyes. An assessment of mosaic regularity confirmed a fairly triangular packing arrangement in the carrier retina, indicating that this was probably an appropriate method for calculating Nc[21]. Nc across the horizontal temporal retina is shown in Figure 4a. The mean Nc and mean ±2 SD of six normal observers (the control eye and 5 from a previous study [31]) and mean Nc calculated from the density measurements of Curcio [1] are shown for comparison. Densities from Curcio et al. were converted to Nc using the following equation:(1)Where m is the number of mm per degree and d is cone density. A value of m of 0.289 was used to convert the data, and assumed that all eyes were emmetropic with 24 mm axial length.


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)

The Nyquist limit of the cone mosaic and adaptive optics corrected visual resolution.a) Nyquist limit of the cone mosaic (Nc) as a function of eccentricity. Lines colored after symbols in inset legend. The black X is the estimate of Nc converted from density of control eye measured in a previous study (Putnam et al., 2005). Dotted magenta line shows mean Nc derived from mean of densities reported by Curcio et al. (1990b). Solid and dashed grey lines are mean and ±2 SD of 6 normal eyes (the control eye and the 5 eyes from Rossi & Roorda, 2010). b) Adaptive optics corrected visual resolution (MARAO) as a function of eccentricity. Minimum angle of resolution (MAR) is shown on left ordinate, while equivalent Snellen acuity is shown on the right. Symbol-subject relations are provided in inset legend. Solid and dashed lines are regression line and 95% confidence intervals fit to the data of 5 normal observers from Rossi & Roorda (2010).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585243&req=5

pone-0057956-g004: The Nyquist limit of the cone mosaic and adaptive optics corrected visual resolution.a) Nyquist limit of the cone mosaic (Nc) as a function of eccentricity. Lines colored after symbols in inset legend. The black X is the estimate of Nc converted from density of control eye measured in a previous study (Putnam et al., 2005). Dotted magenta line shows mean Nc derived from mean of densities reported by Curcio et al. (1990b). Solid and dashed grey lines are mean and ±2 SD of 6 normal eyes (the control eye and the 5 eyes from Rossi & Roorda, 2010). b) Adaptive optics corrected visual resolution (MARAO) as a function of eccentricity. Minimum angle of resolution (MAR) is shown on left ordinate, while equivalent Snellen acuity is shown on the right. Symbol-subject relations are provided in inset legend. Solid and dashed lines are regression line and 95% confidence intervals fit to the data of 5 normal observers from Rossi & Roorda (2010).
Mentions: Cone spacing at the PRLF was larger than normal in BCM carrier eyes. The average minimum ICD measured from the four carrier eyes was 0.79 arcmin (SD = 0.03). JC_1041 had the largest minimum ICD of 0.84 arcmin. JC_1045 had minimum ICD of 0.79 arcmin in each eye. JC_1043 had the lowest ICD, of 0.76 arcmin. Minimum ICD was found less than 3 arcmin from the PRLF for all carrier eyes. An assessment of mosaic regularity confirmed a fairly triangular packing arrangement in the carrier retina, indicating that this was probably an appropriate method for calculating Nc[21]. Nc across the horizontal temporal retina is shown in Figure 4a. The mean Nc and mean ±2 SD of six normal observers (the control eye and 5 from a previous study [31]) and mean Nc calculated from the density measurements of Curcio [1] are shown for comparison. Densities from Curcio et al. were converted to Nc using the following equation:(1)Where m is the number of mm per degree and d is cone density. A value of m of 0.289 was used to convert the data, and assumed that all eyes were emmetropic with 24 mm axial length.

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