Supplementary Material for: A Pilot Study of Smartphone Eye-Tracking for Detection of Positional Nystagmus

Introduction
Detecting positional nystagmus is essential for diagnosing benign paroxysmal positional vertigo (BPPV). Therefore, developing methods to streamline this diagnosis can improve timely patient management and help prevent unnecessary emergency department visits. We aimed to evaluate the accuracy of a smartphone eye-tracking application in quantifying eye movements during positional testing to detect positional nystagmus.

Methods
We recruited patients with positional dizziness suspected of having BPPV from the vestibular rehabilitation clinic and the consult service for dizzy patients (Tele-Dizzy) at Johns Hopkins Hospital. Using an in-house smartphone app (EyePhone), we recorded eye movements during the Dix-Hallpike and supine roll tests. Two expert clinicians reviewed the videos, and a third one adjudicated the disagreements. Eye position data obtained from the EyePhone app were analyzed with an embedded algorithm to identify positional nystagmus. Using the adjudicated expert review as the reference standard, we evaluated EyePhone’s accuracy in detecting positional nystagmus by calculating the sensitivity, specificity, and predictive values.

Results
We recruited ten participants, 60% women, with an average age of 61.8 years. We reviewed 23 positional eye movement videos of participants while undergoing positional testing. The final adjudicated expert review identified positional nystagmus in 3 (13%) videos. The phone application traces indicated nystagmus in all 3 of these videos (Sensitivity = 100% (CI95=44%—100%)) and correctly ruled it out in 20 traces (Specificity = 100% (CI95=84%—100%)). The app demonstrated a positive predictive value of 100% (CI95=43%—100%) and a negative predictive value of 100% (CI95=84%—100%).

Conclusions
This small pilot study shows proof-of-concept that a smartphone eye-tracking app without special phone attachments can detect positional nystagmus.