Pain Phenotypes in Individuals with Neuropathic and Inflammatory Pain Compared to Healthy Individuals

Abstract

Purpose : Neuropathic and inflammatory ocular pain contribute to complex and poorly understood aspects of dry eye symptoms. Diagnostic and treatment challenges arise from a lack of standardization, difficulty differentiating between conditions, and limited therapies, particularly for neuropathic ocular pain (NOP). This pilot study compares clinical manifestations between two ocular pain groups, with the hope that a better understanding will enhance future management of pain.

Methods : Subjects were recruited from 3 groups: NOP, ocular pain related to Sjögren’s Syndrome (SS), and healthy controls. Self-reported symptoms were obtained through validated questionnaires (Ocular Surface Index (OSDI), Neuropathic Pain Symptom Inventory modified for the Eye (NPSI-Eye)), and ocular surface examinations were conducted to evaluate tear parameters (Schirmer’s, Tear Break Up Time (TBUT)), corneal epithelial staining, and nerve function (corneal sensation (0: absent, 1: reduced, 2: normal, 3: increased), and proparacaine challenge test (% pain reduction)). Values from the more severely affected eye were used for all analyses.

Results : Fifteen subjects were enrolled, including 5 with NOP (49.2±9.9 years; 40% males), 5 with SS (44.8±10.4 years; 20% males), and 5 controls (27.6±3.5 years; 80% males). In general, the NOP and SS groups exhibited higher self-perceived dry eye and ocular pain symptoms than controls (OSDI: 63.3±20.8 vs 49.3 ± 30.6 vs 2.1 ± 1.6, p<0.01; NPSI-Eye: 39.2±17.6 vs 23.6±23.7 vs 0±0, p=0.01). Clinically, tear evaporation was comparable across groups (TBUTs: 3.93±3.2 vs 3.3±1.7 vs. 4.9±1.2, p=0.58), while tear production was lowest in NOP followed by SS and controls (Schirmer: 3.8±1.5 vs 13.6±12.1 vs 21.0±8.0, p=0.02), and corneal staining was more pronounced in NOP compared to SS and controls (3.8±3.6 vs 1.6±3.6 vs 0.4±0.5, p=0.21). On the other hand, corneal sensation was reduced in NOP and SS compared to controls (0.8±0.8 vs. 1.4±0.5 vs. 2.2±0.4, p=0.06), and pain improvement with proparacaine was greater in NOP compared to SS (63% vs 22%, p=0.14).

Conclusions : Differences in dryness and pain symptoms, as well as tear and nerve metrics were observed across ocular pain subtypes. Future studies aim at developing a comprehensive assessment that will improve our understanding of ocular pain mechanisms and allow for faster and more efficient diagnosis and management.

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