Purpose: 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.
Methods: 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.
Results: 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.
Conclusions: 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.
Smith-Kettlewell Eye Research Institute, San Francisco, California (CWT, LTL); and Centre for Applied Vision Research, Division of Optometry and Vision Science, City University, London, United Kingdom (CWT).
Christopher W. Tyler Smith-Kettlewell Eye Research Institute 2318 Fillmore Street San Francisco, CA 94115 e-mail: firstname.lastname@example.org