fMRI corroborates photophobia reports in those with chronic ocular pain

Patients with chronic ocular pain often report more intense photophobia sensations than would be expected based on a typical exam. However, those sensations appear to correlate with increased pain-related brain activity on functional magnetic resonance imaging (fMRI).

Study design

This cross-sectional case-controlled analysis looked at the functional neuroimaging of photophobia in patients with chronic ocular surface pain. Eight patients with chronic pain and 8 control patients without pain underwent two fMRI scans while being exposed to light stimuli, first without topical anesthesia and then with anesthesia applied. Pain intensity was reported via questionnaire after each set and was compared with light-activated brain areas on fMRI.

Outcomes

Overall, patients with chronic ocular surface pain reported higher pain intensity ratings and demonstrated more light-evoked activation in pain-related areas on fMRI than patients in the control group. There was also more correlation between pain intensity ratings and light-induced brain activity in pain-related areas for patients in the case group. The application of topical anesthetic slightly decreased light-evoked activation with variable impact on pain ratings.

Limitations

This study was conducted at a Veterans Affairs eye clinic and included only 16 participants, so it is limited by its size and population. Demographic confounders may also exist. Furthermore, as an initial neural imaging study, the clinical significance of the fMRI changes requires more investigation.

Clinical significance

This study is the first to examine neural mechanisms of patients with chronic ocular pain and photophobia and highlights the current limitations in our understanding, diagnosis, and treatment of these patients' conditions. Functional scans like fMRI help us to visualize and quantify the pain response in patients we otherwise clinically deem to have pain disproportionate to exam findings. This study may help us better understand chronic ocular surface pain as a separate clinical entity or subcategory of dry eye syndrome and help us focus the direction of future therapeutics. In addition, it should encourage empathy among practitioners toward their patients with chronic ocular surface pain.

Financial Disclosures: Dr. Daniel Choi discloses financial relationships with Glaukos Corporation (Lecture Fees/Speakers Bureau); Kala Pharmaceuticals (Consultant/Advisor).