Integrating the Numerical Pain Rating Scale (NPRS) with an Eye Tracker: Feasibility and Initial Validation

Abstract

This chapter details the integration of a Numerical Rating Scale (NPRSETI) with a portable eye tracker, enabling the assessment of pain in conditions in which verbal communication and use of hands are limited (e.g., advanced Amyotrophic lateral sclerosis, ALS). After detailing the construction of the NPRSETI, we describe its validation in an outpatient pain clinic. More specifically, thirty chronic pain patients performed the NPRSETI and filled a conventional NPRS (order was pseudo-randomized). Eye movements, including gaze direction and additional eye movement measures (e.g., saccade rate), were recorded, while participants rated their pain using the NPRSETI. The study’s findings indicated no significant differences in pain severity ratings of the NPRSETI and conventional NPRS. Notably, ratings using the two scales were highly correlated (r = 0.99). NPRSETI’s ratings were also strongly associated with participants’ currently experienced pain rating using the Brief Pain Inventory (BPI). The findings provide initial proof of concept for integrating conventional pain rating scales with an eye tracker and validate the NPRSETI compared with the well-validated and commonly used NPRS. Enhanced usability and decreasing costs of eye trackers will ease the additional research mandated to validate these preliminary findings and hopefully advance their integration into clinical practice.