Translation and validation of the Italian version of the Neuropathic Pain Symptom Inventory-Eye (NPSI-Eye) questionnaire for evaluation of ocular neuropathic pain

Purpose: the aim of the study was to translate the Neuropathic Pain Symptom Inventory – Eye (NPSI-Eye) questionnaire into the Italian language and to validate its psychometric properties for assessing the neuropathic component of ocular pain in chronic eye pain patients. Methodology: the translation and validation process were conducted according to standardized methods for cross-cultural adaptation of psychometric tools. Patients presenting to the Ophthalmology Unit complaining of chronic ocular pain were enrolled and completed the questionnaire. Objective assessment of ocular surface dysfunction was performed. Internal consistency and test-retest reliability were determined. Validity was assessed as face validity, construct validity (convergent and divergent validity) and criterion validity. Factor analysis was performed using Exploratory Factor Analysis. Results: the Italian version of the NPSI-Eye questionnaire showed optimal internal consistency (Cronbach's alpha = 0.889, p < 0.001) and test-retest reliability (ICC = 0.991, p < 0.001). Five of the ten symptom items were endorsed by at least 60%. There were moderate-to-high correlations between NPSI-Eye score and comparison pain questionnaires, and lower correlations with dry eye questionnaire scores, demonstrating good convergent and divergent validity. Concerning criterion validity, the questionnaire score showed significant positive correlation with dry eye discordance score (Spearman ρ = 0.530, p < 0.001), and the mean NPSI-Eye score was significantly higher in patients reporting no or partial analgesic response to anesthetic drop instillation (p < 0.001). Conclusions: the Italian version of the NPSI-Eye questionnaire proved to be a valid and reliable tool to measure neuropathic component of ocular pain. It demonstrated psychometric properties comparable to those of the original English instrument in a demographically and clinically distinct population. The NPSI-Eye can be used to assess and quantify distinct dimensions of ocular neuropathic pain across diverse patient groups, offering a standardized means of assessing this complex and often underrecognized pain phenotype.