Purpose: Oscillopsia is a debilitating symptom resulting from involuntary eye movement most commonly associated with acquired nystagmus. Investigating and documenting the effects of oscillopsia severity on visual acuity (VA) is challenging. This paper aims to further understanding of the effects of oscillopsia using a virtual reality simulation.
Methods: Fifteen right-beat horizontal nystagmus waveforms, with different amplitude (1°, 3°, 5°, 8° and 11°) and frequency (1.25 Hz, 2.5 Hz and 5 Hz) combinations, were produced and imported into virtual reality to simulate different severities of oscillopsia. Fifty participants without ocular pathology were recruited to read logMAR charts in virtual reality under stationary conditions (no oscillopsia) and subsequently while experiencing simulated oscillopsia. The change in VA (logMAR) was calculated for each oscillopsia simulation (logMAR VA with oscillopsia - logMAR VA with no oscillopsia), removing the influence of different baseline VAs between participants. A one-tailed paired t-test was used to assess statistical significance in the worsening in VA caused by the oscillopsia simulations.
Results: VA worsened with each incremental increase in simulated oscillopsia intensity (frequency x amplitude), either by increasing frequency or amplitude, with the exception of statistically insignificant changes at lower intensity simulations. Theoretical understanding predicted a linear relationship between increasing oscillopsia intensity and worsening VA. This was supported by observations at lower intensity simulations but not at higher intensities, with incremental changes in VA gradually levelling off. A potential reason for the difference at higher intensities is the influence of frame rate when using digital simulations in virtual reality.
Conclusions: The frequency and amplitude were found to equally affect VA, as predicted. These results not only consolidate the assumption that VA degrades with oscillopsia but also provide quantitative information that relates these changes to amplitude and frequency of oscillopsia.
Keywords: Visual acuity; nystagmus; oscillopsia; simulation; virtual reality.