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Pablo Altschwager, Ronald M Hansen, Anne Moskowitz, Anne B Fulton; Cone Driven Electroretinogram (ERG) in Infants. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):458.
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© ARVO (1962-2015); The Authors (2016-present)
Immaturities in the combining of ON and OFF retinal signals are hypothesized to explain differences between infant and adult photopic ERG responses. We evaluated this possibility by recording responses to brief and long flashes under photopic conditions in 10 week old infants and adults.
We recorded full-field ERG responses to 100 ms and 150 ms pulses of white light (+2.3 log cd s/m2) presented on a steady white rod-saturating background. We also recorded responses to brief flashes (-0.8 to +3.0 log cd s/m2) on a rod saturating background. Amplitude and implicit time of the a-, b- and d-waves were measured. A model of the activation of cone phototransduction was fit to the a-wave to determine cone sensitivity and saturated amplitude. The Hamilton et al. model (Doc Ophthalmol, 2007), which sums Gaussian (OFF) and logistic (ON) functions, was fit to the b-wave stimulus-response data, and G (peak of Gaussian), μ (flash at peak), and B (width of Gaussian) were calculated. Vmax (saturated amplitude of logistic function) and σ (flash that produces ½ Vmax) were also determined. To date, we have tested four full-term 10 week-old infants and 12 healthy adult controls.
For both long duration pulses, implicit time of the infants’ d-wave was significantly longer (p <0.01) than in adults; there was no difference in d-wave amplitude between the groups. For brief stimuli, a-wave amplitude increased with stimulus strength in both groups; cone photoreceptor sensitivity and saturated amplitude in infants were approximately 2/3 of those in adults. The adults showed a b-wave photopic hill that peaked at ~9 cd s/m2 followed by a steep fall-off. The infants’ function was broader, increasing more gradually and declining only slightly at highest intensities. The amplitude at the peak of the Gaussian (G) was the only parameter of the Hamilton model that differed significantly (p <0.01) between infants [58.65±16.16 μV (SEM)] and adults [108.92± 8.10 μV (SEM)].
These results are evidence that in infants, the cone-driven OFF pathway is relatively more immature than the ON pathway.
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