Abstract
Purpose :
Search for an objective approach to measure contrast sensitivity has already been commenced, while the use of eye movements showed a potential solution. The current study aimed to search for the onset time of the optokinetic nystagmus (OKN) quick-phase (QP) in respect to various contrast levels over a range of spatial frequencies (SF) of a moving grating. A trend in timing of the first-OKN-QP for different parameters of a visual stimulus may give a theoretical implementation in the stimulus-presentation-time optimization.
Methods :
To stimulate the OKN response, a 3 seconds sequences of horizontally moving bars with a velocity of 2.5 °/sec, of selected spatial frequencies (SF=1,2,3,4 cpd) and a contrast range C=0.1-58 %, with 22 log-steps in between, were used, whereas the contrast levels were uniformly distributed over 184 trials. Furthermore, as the clinical approach for measuring contrast sensitivity was followed (monocular stimulation), an infra-red filter was installed in front of the left eye of all seven subjects with normal vision. Extracting the OKN events was performed first using a velocity-based algorithm for saccadic (OKN-QP) detection, in continuation with directional and velocity analysis of the slow-phase of OKN (OKN-SP) between two detected OKN-QPs. Next, the search for time of the first OKN-QP after stimulus onset was performed just in trials in which at least two OKN events were detected, requesting a robust response to given parameters of the visual stimulus. On top of that, the found times were clustered with respect to the stimulus parameters (SF, C) for all subjects and the mean time was calculated within a 7.5 % contrast windows.
Results :
The application of Spearman’s correlation, showed a robust propensity of decreasing the mean first-OKN-QP time with increasing contrast level for all four used SFs (R2all>0.76), while the effect of SF was shown as not significant (p=0.1; χ2=6.27). In all SFs combined, the first-OKN-QP time was found to be 361±12 ms for the highest contrast level (C = 58%), whereas it changed towards 525±32 ms for the lowest contrast level (C=0.1 %).
Conclusions :
In conclusion, this study showed an influence of contrast level on the time of OKN onset, hence this study discloses a possible methodological approach of improving the time efficiency of contrast sensitivity testing using the OKN reflexes, by adjusting the presentation time of a visual stimulus of particular parameters.
This is a 2021 ARVO Annual Meeting abstract.