The HMD consisted of a Samsung Galaxy S9 smartphone (Samsung Electronics Co., Suwon, South Korea) and a second-generation Google Daydream View VR headset. The smartphone ran a custom Android application (open-source code available at
https://github.com/imarinfr/opiPhoneHMD). A separate computer ran an R (R Foundation for Statistical Computing, Vienna, Austria) shiny application
8 (open-source code available at
https://github.com/imarinfr/opiApp) which allowed direct control of both the HMD (through the custom Android application on the smartphone) and the Octopus 900 using the Open Perimetry Interface (OPI)—an open-source system designed to control perimeters with the goal of decreasing barriers to perimetry research and increasing access to visual field testing.
8,9 The zippy estimation of thresholds (ZEST) algorithm implemented within the OPI was used to determine individual location sensitivities and was coupled with the Central 26 grid pattern (
Fig. 1) included within the OPI software.
10,11 ZEST thresholding parameters were identical to a prior study by Marín-Franch et al.
12 where they were described in detail. All tests used a Goldmann size V stimulus (1.72° diameter) as opposed to the more conventional size III stimulus (0.43°) due to the greater repeatability and approximately 1 log unit of increased dynamic range observed with size V stimuli.
13–15 Similar to the Octopus 900, subjects entered responses by pressing a single button remote connected to the smartphone via Bluetooth, creating a completely wireless perimeter. Although trial lenses were used for the Octopus 900, there was no refractive correction for patients on the HMD, and they did not wear spectacles while testing. In summary, testing was kept as identical as possible between the Octopus 900 and HMD with the same control software, thresholding algorithm, grid pattern, and similar patient response input.
The study was comprised of two arms. In the first arm, ocular healthy and POAG subjects were tested twice on both the Octopus 900 and HMD. Test eye and test order were randomized (if both eyes for POAG patients met inclusion and exclusion criteria), and the perimeters were alternated with a minimum 5-minute break between each visual field test. Following testing on both the HMD and Octopus 900 perimeters, all participants were asked which system they preferred.
The second arm of the study consisted of retrospective data analysis collected from previously published studies. We used visual sensitivities from three previous research studies: VIPI
14, VIPII
15, and the OPI Octopus 900 control database.
12 These data were analyzed as described below in the Statistical Analysis section, and their relation to the results from the HMD were explored.