Alawa et al. constructed a smartphone-based visual field screening device with the goal of performing frequency doubling testing in a mobile device. They compared results from their instrument to results from the FDT, a commercial frequency doubling instrument, in 19 eyes of ten glaucoma patients, and found no statistically significant differences. The authors conclude that they have constructed a low-cost, portable visual field screening device that produces comparable results to the Humphrey Zeiss FDT and may be used as an easily accessible screening tool for glaucoma.
The authors seem to be focused on producing a device that can be used in community- based and internationally based glaucoma screening in settings where electrical power might not be available. Frequency doubling perimetry has been used in population screening for potentially blinding eye disease not restricted to glaucoma1 and may serve the authors well if employed and interpreted in ways that have worked in the past, for instance focusing on high risk populations, and requiring confirmation tests when encountering apparently abnormal results. It may also be worth noting that population screenings for glaucoma may lead to detection of significant amounts of non-glaucomatous visual field loss as well.2,3
This study has significant limitations. The authors have provided no estimates of the size of differences between the two compared devices that might have been detected, given the number of eyes tested. However, they must be aware that their sample size probably was not large enough to support useful quantitative conclusions regarding inter-device comparability. The study was also limited by lack of a control group. The authors point out that their device differs from the commercially available FDT in multiple ways, differences that, until proven otherwise must be viewed as necessitating collection of normative data specific to their device. Unfortunately, the authors seem to have based their screening strategy on an age-adjusted normative study previously performed using the Humphrey Zeiss FDT,4 and, until proven otherwise, they should assume that their screening device will have a different level of specificity than that of the commercial FDT instrument. It also is not clear that their device's limited, eight bit contrast resolution is adequate, if their goal is to produce comparable results to the Humphrey Zeiss FDT.
In conclusion, the primary value of this paper may be that it suggests that FDT testing might be possible using a head-mounted smartphone. Further work will be necessary before we actually know if such an application is now possible or must await further developments in smartphone display technology.
Vincent Michael Patella is at present a paid consultant to the manufacturer of the FDT, Carl Zeiss Meditec Inc, Dublin, CA, USA.