Prolonged Aftersensations to Thermal Noxious Stimulation as a Screening Tool for Central Contributions to Chronic Ocular Pain.

Abstract

Painful aftersensations (AS) are sensations that persist after termination of a noxious stimulus, and prolonged AS may reflect abnormal somatosensory processing. We aimed to validate AS as indicators of central nervous system processing abnormalities in individuals with chronic ocular pain (COP). We examined two cohorts (Groups 1; n=278 and 2; n=64) who underwent an ocular surface examination, quantitative sensory testing (QST), and pain symptom assessment. Individuals were asked to rate pain intensity and unpleasantness (0-100) of AS at 15s and 30s after termination of a repeated stimulus protocol at two sites (forehead and forearm). Ratings >0 were considered positive for AS. Using Group 1 data, exploratory regression analyses determined which AS metrics most strongly related to central neuropathic-like or nociplastic ocular pain (NOP). The presence of unpleasant AS at 15 and 30s after hot pain on the forearm accounted for the most variability in indicators of NOP (i.e., scores on the Neuropathic Pain Symptom Indexmodified for the Eye (NPSI-Eye) and response to anesthetic eyedrops). We assessed the robustness of these AS metrics as indicators of NOP using data from a separate cohort (Group 2), by comparing NPSI-Eye scores, response to anesthetic eyedrops, and ocular signs (Schirmer's scores, tear film, and corneal fluorescein staining) between those with AS and those who did not report AS. The presence of AS was related to greater NPSI-Eye scores and persistence of eye pain after local anesthetic, but not to tear dysfunction signs, suggesting AS can differentiate patients with potential central mechanisms of COP. PERSPECTIVE: The presence of unpleasant aftersensations at 15 and 30 seconds after removal of a noxious hot stimulus was associated with other indicators of central somatosensory abnormalities in two disparate populations. This suggests that AS could be a clinical screening tool for central contributors to ocular pain.