Photophobia is a debilitating clinical condition that disrupts the ability to use vision for everyday tasks in bright lighting conditions. The goal of the study is to develop a methodology to study the neural basis of photophobia and the contribution of the melanopic pathway to its etiology with differential chromatic responses by means of standard electroencephalographic recording equipment.
We introduce and validate the approach of recording wavelength-specific electroretinographic (ERG) responses from the face electrodes of the high-density whole-head electroencephalography recording system under light-adapted conditions.
ERGs recorded in this way to whole-field chromatic stimuli exhibit striking differences between the photophobic and non-photophobic groups. The control responses were consistent with photopic intensity in peak time, and in the ordering of peak times as a function of wavelength condition, indicating a predominantly cone source of the signals. The photophobic responses, on the other hand, were substantially slowed relative to controls, with the peak times conforming to a different order as a function of wavelength condition than controls, implying that the cone response has been suppressed and that the responses derived from a different photoreceptor system consistent with mediation by melanopic retinal ganglion cells.
The results will be important for determining the neural pathways involved in photophobia and potential approaches to its treatment on the basis of this etiology.