Beacon: Designing a Portable Device for Self-Administering a Measure of Critical Flicker Frequency

Critical flicker frequency (CFF) is the minimum frequency at which a flickering light source appears fused to an observer. Measuring CFF can support early diagnosis of minimal hepatic encephalopathy (MHE), a condition affecting up to 80% of people with cirrhosis of the liver. However, adoption of CFF measurement in clinical practice has been hampered by the cost of a device for measuring CFF and the need for specialized training to administer the test. This paper presents Beacon, a portable, inexpensive device that enables people to measure their own critical flicker frequency. We adopt a mixed-methods approach to informing and evaluating the design of and potential opportunities for Beacon. We first report on a two-part formative study with 10 participants to evaluate the choice of certain parameters in the design of Beacon. We then report on a study of 41 healthy adults ranging from 18 to 99 years of age, finding that Beacon performs on par with Lafayette Flicker Fusion System, an established medical device, achieving a pearson correlation coefficient of 0.88. We finally report on a focus group with five hepatoligists who work with patients with cirrhosis of the liver, using our initial prototype development to examine their perspectives on potential opportunities and challenges in adoption of a device like Beacon. We discuss Beacon as an exploration of reframing critical flicker frequency measurement from a clinical screening tool into a self-administered self-tracking measure, thereby drawing upon and contributing to research in the health and personal informatics.