An fMRI case report of photophobia: activation of the trigeminal nociceptive pathway

Abstract

Photophobia, or painful oversensitivity to light, occurs in a number of clinical conditions, which range from superficial eye irritation to meningitis. In this case study, a healthy subject with transient photophobia (induced by the overuse of contact lenses) was examined using functional magnetic resonance imaging (fMRI). While being scanned in a darkened environment, the subject was presented with intermittent 6-s blocks of bright light. The subject was scanned twice, once during his photophobic state and once after recovery. The subject reported that the visual stimuli produced pain (pain intensity=3/10 and unpleasantness=7/10) only during the photophobic state. During photophobia, specific activation patterns in the trigeminal system were seen at the level of the trigeminal ganglion, trigeminal nucleus caudalis, and ventroposteromedial thalamus. The anterior cingulate cortex, a brain structure associated with unpleasantness, was also active during photophobia. After recovery from photophobia, no significant activations were detected in these areas. This study may contribute to a better understanding of the pathways involved in photophobia in the human condition.

Figures

Figure 1

fMRI activation during photophobia across three levels of the trigeminal system. Scanning results from during the photophobic state (“Affected” in green) and after recovery (“Recovered”) are shown. Regions of interest (highlighted by light blue circles) are shown across three different viewing planes. Significant activation (p

Figure 2

A) fMRI activation of the right anterior cingulate cortex (ACC) with the presentation of light during the photophobic state, but not after recovery. The top row of sagittal images shows activation maps (p