Clinical Dynamic Visual Acuity (DVA) test

Based on the previous studies, the clinical DVA test was done with passive head movement to minimize the effect of central preprogramming on gaze control [25–27]. We used LCD optotype NIDEK SC-1600 that displays five letters in a single line with corresponding logMAR (logarithm of the Minimum Angle of Resolution), with a change in acuity of 0.1 logMAR between each line. The letters of equal legibility were displayed in random sequence to avoid memorization. The subjects were seated in a chair 5m from the monitor and ask to identify letters, beginning with line 0.1 (decimal value), continuing for successive lines until the subject missed three of the five optotypes on a line. The logMAR values of this line (“missed three” score) and that of the lowest line on which all optotypes were correct were recorded. This was done under the following conditions: head stationary (static visual acuity–SVA) and head passively rotated sinusoidally 20° from center to the left and right (dynamic visual acuity—DVA) to the beat of a metronome at 1Hz and 2 Hz (previously recommended parameters known to challenge the VOR) [25–32]. The 2Hz has been considered as a more challenging condition. The amplitude of a head movement was controlled by the use of accelerometer and gyroscope sensor WMS 3.0, Princip a.s., Prague, providing feedback for the examiner to achieve accurate head movements. A dynamic visual acuity score (DVA score) was calculated as a difference between SVA and DVA, in chart lines on the logMAR chart [30]. The principle of this test does not allow to evaluate differences between right and left head rotation. According to Rine et al., we defined the decline of DVA ≥2S.D. above the normative mean as abnormal [32], in our case, it represents DVA score higher than one.

In addition to the objective measurement of the clinical DVA test, the presence of oscillopsia was estimated using the question “Have you ever had problems with wobbling, jumping or blurring of vision?”.