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Michael F. Marmor, Fang Tan, Erich E. Sutter, Marcus A. Bearse; Topography of Cone Electrophysiology in the Enhanced S Cone Syndrome. Invest. Ophthalmol. Vis. Sci. 1999;40(8):1866-1873.
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purpose. To investigate the topography of cone electroretinographic (ERG)
responses in the enhanced S cone syndrome (ESCS).
methods. A 19-year-old female with ESCS who was one of the original
cases defining the syndrome was studied. Full-field, focal
(Maculoscope) and multifocal (VERIS) ERGs were performed using white
light. Multifocal ERG responses were also generated with red and blue
stimuli and with a slow m-sequence to elicit off-responses. Results
were analyzed by averaging data in rings at increasing eccentricity
from the fovea and compared to data recorded identically from a normal
results. The full-field ERG from this patient showed typical large slow photopic
waveforms and was unchanged from recordings made 9 years earlier. The
focal ERG showed signals of borderline low amplitude from the fovea
with the multifocal ERG, the ESCS responses from the central macula had
a relatively normal waveform, and those 9° to 20° from fixation
showed the prolonged waveform that characterizes the full-field ERG.
Responses were larger to blue light than red light in ESCS in both
center and periphery. The central ESCS responses were relatively normal
in timing to both red and blue light, whereas the peripheral ESCS
responses were markedly delayed to both. Off-responses were seen in
ESCS only near the foveal center.
conclusions. The marked differences between central and peripheral ERG responses in
ESCS suggest that there are different distributions of S, L, and M
cones in these regions and that S cones may feed into different neural
pathways in the center and periphery. It was postulated that in ESCS, S
cones may partially replace L and M cones centrally and feed into the
usual S cone pathways. In the periphery, however, there is little L and
M cone b-wave activity in ESCS, and S cones may usurp both the space
and neural pathways of the rods.
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