Aftersensations as an indicator of nervous system abnormalities in individuals with ocular pain

Abstract

Purpose : Ocular pain (OP) is a prevalent symptom linked to a diverse array of disorders, emphasizing the importance of identifying individual contributors to administer targeted treatment. Few diagnostic tests are available to examine whether neuropathic mechanisms contribute to OP. We examined whether the presence of aftersensations (AS) correlated with other signs of neurological dysfunction in individuals with OP.

Methods : Individuals (n=64) recruited from the Miami Veterans hospital filled out questionnaires regarding ocular symptoms and underwent an ocular examination and functional magnetic resonance imaging (fMRI) scan. Temporal summation (TS) of pain was evaluated through quantitative sensory testing conducted on the forearm and forehead. Pain and unpleasantness ratings 15 and 30 seconds after TS (rated on a numerical rating scale; range 0-100) were used to examine AS. AS at a particular time (15/30 seconds) and location (forehead/forearm) were dichotomized as present (>0) or absent (=0) for both intensity and unpleasantness. Event-related fMRI was performed using a 3T Siemens MAGNETOM Vida scanner (Erlangen, Germany) to measure neural responses to light-induced pain. Relationships among AS, ocular symptoms and signs, and fMRI activity were examined.

Results : The study population had a mean age of 56±10 years, 68% were male, 71% White, and 49% Hispanic. 44 subjects (69%) reported OP (recall of average pain rating last week ≥1; range 0-10). The AS metric most closely related to ocular symptoms (5-Item Dry Eye Questionnaire, β=0.41 p<0.001) was unpleasantness at 15 seconds on the forearm. Individuals with a positive AS at this site/time had higher Neuropathic Pain Symptom Inventory-Eye questionnaire scores (30±20 vs. 12±19, p<0.001; range 0–100) than those with negative AS. In a neuroimaging sub-analysis of individuals with OP (n=29), AS detected during QST (n=20) were associated with less light-induced fMRI activity in several brain regions (e.g., primary (S1) and secondary (S2) somatosensory, insula, thalamus, etc.) and greater responses in other regions (e.g., intracalcarine cortex) compared to individuals without AS (n=9).

Conclusions : AS align with other indicators of nervous system dysfunction in individuals with OP. More studies are needed to examine how this clinical metric can be translated into improved treatment algorithms.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.