Photoreceptor topography and cone-specific electroretinograms

Abstract

It is implicit in many cone-specific ERG studies that the amplitude is proportional to the numbers of cones stimulated. The objective of these experiments was to test this idea by comparing ERGs obtained from different areas of the retina with histological data on cone-density distributions. The histology (Curcio et al., 1990) shows that the cumulative number of cones in the human retina increases exponentially with stimulus diameter between 0- and 40-deg eccentricity. L-, M-, and (L+M) cone-driven 30-Hz ERGs were obtained from a series of stimuli with one of the following configurations: (1) Circular stimuli of different angular subtense up to 70-deg diameter. (2) Annuli with 70-deg outer diameter but variable inner diameter. (3) Annuli of constant area but increasing eccentricity. Cone contrasts were equalized for each stimulus condition. The modulated and nonmodulated regions of the screen had the same mean hue and luminance. The data suggest that the L+M cone ERG amplitude increases with stimulus diameter in direct proportion to the estimated number of cones stimulated. Furthermore, the total L+M responses appear to be predicted from individual L and M responses by simple linear summation for both the disc and annular stimuli.

L‐ and M‐cone input to 12Hz and 30Hz flicker ERGs across the human retina

“…The existence of an L:M ERG ratio close to unity for the 12 Hz response would appear to indicate that there is a balanced contribution from L-and M-cones to this response consistent with the idea that it is mediated by cone-opponent, parvocellular processing pathways (Kremers and Link, 2008). ERG cone amplitude ratios have been shown to be directly correlated with L:M cone ratios determined by anatomical means (Usui et al, 1998;Brainard et al, 2000;Kremers et al, 2000Kremers et al, , 2003Kremers, 2003;Murray et al, 2004;Hofer et al, 2005). In normal trichromats L:M cone ratios have been shown to vary widely across different subjects (Brainard et al, 2000;Carroll et al, 2002;Hofer et al, 2005).…”

“…For this stimulation frequency, L:M ERG ratios are greater than unity, ranging from approximately 4:1 for the smaller central and more peripheral annular stimuli, increasing up to 8:1 for the largest 70°diameter stimuli. The higher L:M ERG ratios obtained for 30 Hz are more likely to reflect anatomical ratios of L-and M-cones and their inputs to non-opponent, luminance processing mechanisms (Usui et al, 1998;Brainard et al, 2000;Kremers et al, 2000Kremers et al, , 2003Carroll et al, 2002;Kremers, 2003;Murray et al, 2004;Hofer et al, 2005). However, it is the variation of the L:M ERG ratio as a function of the region of the retina that is stimulated that is of note here.…”

“…Traditionally, the ERG has been viewed as a measure of distal retinal function. Responses derived from photoreceptor stimulation and their amplitude ratios were found to be closely correlated with known cone spectral sensitivities and L:M cone ratios determined by direct anatomical imaging techniques (Usui et al, 1998;Brainard et al, 2000;Kremers et al, 2000Kremers et al, , 2003Carroll et al, 2002;Kremers, 2003;Murray et al, 2004;Hofer et al, 2005). However, studies have shown that ERGs also reflect inner retinal function (Baron, 1980;Donovan and Baron, 1982;Bush and Sieving, 1996;Viswanathan et al, 1999Viswanathan et al, , 2000Viswanathan et al, , 2002.…”

Incremental and decremental L- and M-cone-driven ERG responses: I Square-wave pulse stimulation

“…In a number of studies there have been attempts to identify and isolate long-(L), middle-(M), and short-(S) wavelength-sensitive cone mechanisms within the ERG response [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. In many of these experiments, cone isolation was usually achieved either by chromatic adaptation [18] or silent substitution [25] methods.…”

Multifocal electroretinographical changes in monkeys with experimental ocular hypertension: a longitudinal study

“…This procedure implies that similar numbers of cones are stimulated by the macular hexagon and by each ring. We estimated the numbers of stimulated cones in the central hexagon and the different rings for human subjects based on anatomical data [30,31]. The cone densities in macaques are similar to those in humans [32].…”