Abstract
Purpose :
To present a novel, mobile-phone application (eyeFusion) that can objectively quantify critical flicker fusion (CFF) thresholds, within the confines of smartphone hardware limitations. CFF has long been established as a sensitive measure of a visual conduction time, which becomes abnormal in retinal and optic nerve disorders.
Methods :
The testing paradigm implemented (Fig. 1) consists of a ring of twelve circular stimuli (0.3 inches in diameter, which subtends 1.56 degrees visual angle for the diameter of each circular stimulus) at different grayscale contrasts, randomized in location, each centered on a median grayscale intensity background. Nine stimuli oscillate at specified temporal frequencies, while the remaining three do not flicker and are presented at zero percent contrast. The objective of the user is to tap each of the stimuli that appear to flicker, which then eliminates them from the screen. A photodiode was used to measure the true temporal frequency presented at programmed temporal frequencies of 1, 7.5, 15, and 30 Hz on the iPhone 5c, iTouch 5, and iPad Air. The discrete Fourier transform was computed to characterize the frequency response of each measured signal. Each signal was fitted for a square wave, with the correlation coefficients measured.
Results :
For the 1, 7.5, 15, and 30 Hertz signals respectively, the dominant peak frequencies computed were 0.98, 7.49, 15, and 30.01 Hz on the iPhone, 0.98, 7.50, 14.99, and 29.98 Hz on the iTouch, and 0.99, 7.50, 15, and 30 Hz on the iPad. Correlations of the 1 Hz signals with fitted square wave were r2 = 0.98 for all three devices. For the iPhone, iTouch, and iPad respectively, r2 for the 7.5 Hz signals were 0.87, 0.84, and 0.85; 0.72, 0.65, and 0.64 for the 15 Hz signals, and 0.46, 0.35, and 0.42 for the 30 Hz signals. Furthermore, 30 Hz flicker stimuli on average only reached 90.6% of the value of the intended contrast.
Conclusions :
These results demonstrate the technical feasibility of flicker fusion testing with smartphone and tablet devices. Hardware limitations restrict the temporal frequencies that can be presented. 30 Hz oscillations have reduced accuracy in the temporal and intensity domain of pixel presentation. With confirmation that a robust signal can be presented at 7.5 Hz, eyeFusion provides a useful approach to efficiently quantify flicker fusion thresholds on large populations.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.