To assess the role of conditioned pain modulation (CPM), a measure of inhibitory pain pathways, in dry eye management (DE), researchers conducted a cross-sectional study of 268 patients from October 2017 to August 2018. They measured DE metrics through questionnaires and an ocular surface exam. CPM was evaluated with a noxious thermal stimulus, followed by a noxious conditioning stimulus (water bath) and then by the original noxious stimulus at the forehead and forearm. Pain inhibition was considered a normal response. CPM intensity (r = −0.21; P<.05) and unpleasantness (r = −0.18; P<.05) at the forehead was significantly related to Dry Eye Questionnaire score. CPM unpleasantness at the forehead was also significantly associated with average eye pain intensity over 1 week (r = −0.20; P<.05) and tear breakup time (P = -0.21; P<.05). CPM unpleasantness at the forearm was significantly tied to average eye pain intensity over 1 week (r = −0.26; P<.05) and evoked pain to wind (r = −0.21; P<.05) and light (r = −0.24; P<.01). The relationship between a more robust CPM response and worse DE metrics indicates that CPM is intact or even upregulated in DE, the researchers noted.
