Purchase this article with an account.
M. Hebert, A.-M. Gagne; Prior Light History Impact on Rod ERG: Modulation Disparities Between Patients With Winter Depression and Normal Controls. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5311.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
In normal controls the rod system appears to adapt to the amount of light received just prior to ERG testing (Gagne et al. Psychiatry Res, 2007). In brief, following an exposure to 5 lux for 60 min, we observed a higher ERG maximal rod response when compared to responses obtained after expositions of 60 min to 100 lux and 10,000 lux which did not differ. We proposed that this effect could be linked to light triggered dopamine production which would be already saturated in the 100 lux condition. Considering that patients affected with winter depression demonstrate lower rod sensitivity (Hebert et al. Psychiatry Res, 2004) our goal was to challenge patients' ERG rod response to the same light history protocol in winter when they are depressed and in summer when they are remitted.
Eleven healthy subjects and 12 diagnosed patients were exposed for 60 min to three different light intensities (10,000 lux ,100 lux and 5 lux) presented in a random order and separated by an interval of at least 1 day. Following a 30 min dark adaptation period, rod ERG was acquired with a DTL fiber in non dilated eyes, using blue-green light flashes provided by an Espion system Color Dome (Diagnosysllc, Lowell, MA, USA). Various intensities of stimulation (range of 4 log units) were used to generate a luminance response curve from which the saturating rod ERG response was identified (Vmax). All participants were tested in winter and summer.
In normal controls, as expected from the previous study, a 3-way ANOVA revealed an increase of 11.5% of rod Vmax response in the 5 lux condition (P<0. 0001) when compared to the 100 and 10,000 lux conditions which did not differ. In patients, a reduction of 11.3% of the rod Vmax reponse was observed in the 10,000 lux (P<0. 0001) when compared to the 5 and 100 lux conditions which did not differ significantly. No change across seasons could be observed. Of note, 66% of patients showed a 10% decrease (in both seasons) in the 10,000 lux condition, whereas only 1 normal control subject showed the same result, but in winter only.
At the moment, we have no explanation as why patients affected with winter depression demonstrate a decreased rod response after a 10,000 lux exposure and no increase after a 5 lux exposure when compared to 100 lux. However, this particular pattern of rod response modulation with prior light exposure may represent a marker in these patients, since it was observed in both the remitted state and depressive episode.
This PDF is available to Subscribers Only