Clinical functional magnetic resonance imaging of photophobia in individuals with chronic ocular pain: provisional analysis

Abstract

Purpose : Individuals with neuropathic ocular pain are similar to those with chronic neurological disorders in that they often report symptoms of sensory hypersensitivity, such as increased corneal sensitivity and evoked pain to light. The latter, often referred to as "photophobia", is a particular topic of interest in the realm of chronic pain. Specifically within ocular pain, patients with discordant symptoms are more likely to report photophobia, which suggests underlying contribution by centrally-sensitized mechanisms in response to light. In this study, we hypothesized that trigeminal sensory processing contributes to photophobia in patients with neuropathic ocular pain.

Methods : fMRI was used to evaluate brain pathways in individuals with neuropathic ocular pain. Subjects were screened to meet criteria for 1 of 2 groups: dry eye symptoms with chronic ocular pain and photophobia (n=8 cases) and no ocular pain or photophobia (n=8 controls). Subjects were presented with intermittent light stimuli during two scans: 1) a control scan after artificial tear instillation, and 2) after pharmacological blockade of afferents in the ocular surface with instillation of 0.5% proparacaine. Pain ratings elicited by light were acquired, and clinical ophthalmic signs and symptoms were recorded.

Results : Light-induced greater group-level activation in cases vs. controls in the somatosensory cortices (S1), spinal trigeminal nucleus, bilateral insula, anterior mid-cingulate cortex (aMCC). Patients with chronic ocular pain and photophobia reported higher pain intensity and unpleasant ratings to light than controls. Correlations between activity and ratings were greater in cases than controls.

Following proparacaine in cases, decreased light-related activation was observed in S1 and MCC. At the group level, cases demonstrated decreased pain intensity and unpleasantness ratings to light following proparacine, but half of cases did not show a decrease in these ratings.

Conclusions : The trigeminal nociceptive system may contribute to photophobia symptoms among individuals suffering from chronic ocular pain. We demonstrate partial modulation of cortical structures in this pathway by means of topically applied anesthetic to the eyes. Further understanding of the modulatory interactions underlying ocular pain and photophobia is critical for developing effective therapies and guiding treatment plans.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.