Comparative Analysis of Oculography Methods For The Diagnosis Of The Vestibular System

There are various eye-tracking methods and the most common among them are methods of videooculography (VOG) and electrooculography (EOG). These methods are based on completely different physical principles, and accordingly, the signals received during the eye movements recording have different noise sources. Eventually, both methods register the same mechanical movement, and as respect, they should give consistent results. In this regard, the experimental study and analysis of accuracy of VOG and EOG while visual saccades registration performed using these methods of oculography simultaneously were carried out. 12 horizontal saccades to the left with an average amplitude of Vleft = 150±50 deg/s and 10 saccades to the right with an average amplitude of Vright = 160±50 deg/s were recorded simultaneously by these two methods. The signals were processed by a low-pass filter with a cut-off frequency of 10 Hz and synchronized in time using crosscorrelation. Further, the saccades were averaged separately for each system and the left-right direction. The comparison of visual saccades was carried out using a linear regression model of the dependence of the eye velocity, recorded by EOG, on the eye velocity, recorded by VOG. A statistically significant good agreement of the eye velocities recorded using EOG and VOG during horizontal saccades was found. The obtained results of experimental studies have shown that despite the completely different physical principles these two methods based on and the presence of measurement errors of different nature, on average, the results of the eye movement registration by VOG and EOG systems are in excellent agreement with each other. The advantage of using EOG for measuring saccades and evaluating the vestibulo-ocular reflex (VOR)is shown

Fitting the determined impedance in the guinea pig inner ear to Randles circuit using square error minimization in the range of 100 Hz to 50 kHz

Objective. Several lumped and distributed parameter models of the inner ear have been proposed to improve vestibular implant stimulation. The models should account for all significant physical phenomena that influence the current propagation, such as the electrical double layer (EDL) and medium polarization. The electrical properties of the medium are reflected in the electrical impedance; therefore, the study aimed to measure the impedance in the guinea pig inner ear and construct its equivalent circuit. Approach. The electrical impedance was measured from 100 Hz to 50 kHz between a pair of platinum electrodes immersed in 0.9% NaCl saline solution using sinusoidal voltage signals. The Randles circuit was fitted to the measured impedance in the saline solution in order to estimate the EDL parameters (C, W, and R-ct) of the electrode interface in saline. Then, the electrical impedance was measured between all combinations of the electrodes located in the semicircular canal ampullae and the vestibular nerve in the guinea pig in vitro. The extended Randles circuit considering the medium polarization (R-i, R-e, C-m) together with EDL parameters (C, R-ct) obtained from the saline solution was fitted to the measured impedance of the guinea pig inner ear. The Warburg element was assumed negligible and was not considered in the guinea pig model. Main results. For the set-up used, the obtained EDL parameters were: C=27.09*10(-8) F,R-ct=18.75k Omega.The average values of intra-, extracellular resistances, and membrane capacitance were R-i=4.74 k Omega, Re=45.05k Omega, Cm=9.69*10(-8)F, Significance. The obtained values of the model parameters can serve as a good estimation of the EDL for modelling work. The EDL, together with medium polarization, plays a significant role in the electrical impedance of the guinea pig inner ear, therefore, they should be considered in electrical conductivity models to increase the credibility of the simulations