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Roa Al-Abdalla, Nabin Joshi, Jennifer Nguyen, Kenneth J Ciuffreda, Suresh Viswanathan; The photopic negative response in mild traumatic brain injury. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4281.
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The photopic negative response (PhNR) is a slow negative potential of retinal ganglion cell origin in the cone-mediated flash electroretinogram (ERG). The purpose of this study was to examine whether the PhNR is altered in patients with a diagnosis of mild traumatic brain injury (mTBI).
PhNRs were recorded using DTL fiber electrodes with a Ganzfeld System (Diagnosys LLC) from 9 patients with mTBI (22-45 years of age) and 21 control subjects (22-49 years of age). Stimuli consisted of brief (<5 ms) red flashes ranging from -2.2 to 0.8 log phot cd.s/m2 on a 2 log scot cd/ m2 blue background. The PhNR amplitude was measured at its trough from baseline and the b-wave, which originates from cone bipolar cell activity, was measured at its peak from the preceding a-wave. Both the PhNR and b-wave amplitudes were plotted as a function of flash intensity and fitted with the Naka-Rushton equation, V(I) = (Vmax*In)/(In+Kn), where V is the response at intensity I, Vmax is the saturated amplitude, n is the slope and K is the semi-saturation constant (intensity at 50% of Vmax). Vmax, n and K derived from the fits were compared between mTBI patients and controls.
For the PhNR intensity response function, n was significantly larger (p=0.03) and K was significantly smaller (p=0.036) in the mTBI group (n=1.6, K=0.13) relative to the control group (n=0.99, K=0.20). K also showed a significant negative correlation with n (r=0.18, m=-0.16, p<0.001). The Vmax of the PhNR and all Naka-Rushton fit parameters of the b-wave were not significantly different between mTBI patients and control subjects.
A selective increase in the slope of the PhNR intensity response function of mTBI patients with a corresponding decrease in the semi-saturation constant indicates elevated sensitivity of the cellular generators of the PhNR in patients with mTBI. This finding may suggest a potential pre-cortical basis for photosensitivity in mTBI.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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