Reem Almagati¹ (), Michelle Kelly Pham¹, Jorge Otero-Millan^1,2; ¹University of California, Berkeley, ²Johns Hopkins University

Heterophoria refers to the angular difference between ocular vergence and vergence demand of a given target when disparity signals are absent. A common clinical method of measuring heterophoria is the alternating cover test. We utilized virtual reality (VR) to test heterophoria, in three different versions of a virtual cover test: monocular continuous target, (dark) no target in either eye, and a monocular flashing target that was on only 50 milliseconds every 1 second. Eight subjects viewed stimuli using the Varjo XR-4 VR headset while we tracked their eye movements using OpenIris. Participants were seated with their chin rested on a chinrest to minimize head movements. Monocular calibration was performed prior to each session. We tested the relaxation of vergence after a 5 second binocular period of forced convergence or divergence. We measured the average vergence angle reached between 8 and 10 seconds after the cessation of the binocular period. Our results show a slightly convergent (5.3±2.2 degrees) vergence angle in the no target condition (tonic vergence) consistent with findings in the literature. The vergence angle in the continuous target condition was 1.7±1.9 degrees. Interestingly, the vergence angle in the flashing condition remained comparable to the non-flashing condition (2.4±1.7 degrees) and far from the value of the no target condition. This suggests that the crosslinks between accommodation and vergence are sufficient to hold vergence during very brief stimuli that may not be enough to drive accommodation alone.

Acknowledgements: NEI training grant 5T32EY007043-43 NEI R00EY027846 Hellman Fellows Fund