Clinical Neuroimaging of Photophobia in Individuals With Chronic Ocular Surface Pain

Abstract

To examine neural mechanisms underlying photophobia in individuals with chronic ocular surface pain by using functional magnetic resonance imaging (fMRI). Cross-sectional case/control analysis. A total of 16 individuals from the Miami Veterans Affairs eye clinic underwent comprehensive ocular surface evaluations and were surveyed for ocular surface symptoms. Case patients included patients who reported chronic ocular surface pain symptoms and light sensitivity at least most of the time over 1 week. Controls included persons without chronic ocular surface pain who reported no or minimal light sensitivity. All patients viewed light stimuli during 2 fMRI scans, one before and one after topical anesthetic instillation, and rated their level of pain intensity to the stimulus at the end of each scan. Areas of brain activation in response to light stimuli presentation were correlated with pain responses and examined post- vs pre-anesthesia. Case patients (n=8) reported higher pain intensity ratings than controls (n=8) in response to light stimuli during fMRI. Case patient ratings correlated more with light-evoked activation in pain-related areas within the trigeminal brainstem, primary somatosensory cortex (S1), anterior mid-cingulate cortex (aMCC), and insula than in controls. Topical anesthesia led to varying responses in pain ratings among case patients as well as decreased light-evoked activation in S1 and aMCC. The trigeminal nociceptive system may contribute to photophobia in individuals with chronic ocular surface pain. We demonstrate modulation of cortical structures in this pathway with topically applied anesthetic to the eyes. Further understanding of modulatory interactions that govern ocular surface pain and photophobia is critical for developing effective, precision-based therapies.