After VEP recording was explained to the patient and control groups, the keypoint electromyography device was used for measurement. We comply with the international society for clinical electrophysiology of vision (ISCEV) standards for a few differences [29 (link)]. Our differences were reversal rate and sweep speed. These changes were used in this way to obtain the most optimal waveform with laboratory conditions and equipment. The person was placed in front of the monitor screen with an eye-screen distance of 100 cm. The ground electrode was connected to the right wrist. The scalp needle electrode was used as an active electrode. Head circumference measurements were made. 10% of the obtained value was taken by measuring between nasion and inion in accordance with the international 10–20 system. The active electrode is placed on the occipital scalp over the visual cortex at Oz with the reference electrode at Fz. During the measurement, a scalp needle electrode was used to lower the impedance and obtain a more objective wave. The monocular recording was performed by covering one eye with an eye pad.
VEP recording was made with a 12 × 16 checkerboard pattern reversal pattern. Pattern-reversal VEPs elicited by checkerboard stimuli with large, 1 degree (°), and small, 0.25° checks. The black and white checks change reverse abruptly, with no overall change in the luminance of the screen. The mean luminance was 50 (cd m−2). The contrast between black and white squares was high and Michelson contrast2 was 80 (%). Pattern-reversal VEPs were obtained using a reversal rate of 3 reversals per second (rps), 200 averaging settings. The settings of the device were pes frequency 10 Hz, treble frequency 0.1 kHz, and sweeping speed 30 ms/min. The patient was asked to look at the midpoint on the screen as the fixation point. Patients who had difficulty in cooperation were excluded from the study group. Impedance was checked before each procedure and recording was started if it was below 5-kilo ohms. During the registration of the patients, care was taken to ensure that the ambient conditions such as the lighting of the room were the same. After the recording samples were taken from the computer, the electrodes were removed and the procedure was terminated.
In the VEP recorded, N75, P100, and N135 waves were plotted, and latencies and the peak-to-peak amplitude of the P wave were measured. Latencies are given in milliseconds (ms) and amplitudes in microvolts (μV). These peaks are designated as negative and positive followed by the typical mean peak time. We used a negative waveform and measurements were taken on this waveform. The standard measure of VEP amplitude is the height of P100 from the preceding N75 peak.
VEP recording was made with a 12 × 16 checkerboard pattern reversal pattern. Pattern-reversal VEPs elicited by checkerboard stimuli with large, 1 degree (°), and small, 0.25° checks. The black and white checks change reverse abruptly, with no overall change in the luminance of the screen. The mean luminance was 50 (cd m−2). The contrast between black and white squares was high and Michelson contrast2 was 80 (%). Pattern-reversal VEPs were obtained using a reversal rate of 3 reversals per second (rps), 200 averaging settings. The settings of the device were pes frequency 10 Hz, treble frequency 0.1 kHz, and sweeping speed 30 ms/min. The patient was asked to look at the midpoint on the screen as the fixation point. Patients who had difficulty in cooperation were excluded from the study group. Impedance was checked before each procedure and recording was started if it was below 5-kilo ohms. During the registration of the patients, care was taken to ensure that the ambient conditions such as the lighting of the room were the same. After the recording samples were taken from the computer, the electrodes were removed and the procedure was terminated.
In the VEP recorded, N75, P100, and N135 waves were plotted, and latencies and the peak-to-peak amplitude of the P wave were measured. Latencies are given in milliseconds (ms) and amplitudes in microvolts (μV). These peaks are designated as negative and positive followed by the typical mean peak time. We used a negative waveform and measurements were taken on this waveform. The standard measure of VEP amplitude is the height of P100 from the preceding N75 peak.
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