Recording Horizontal Saccade Performances Accurately in Neurological Patients Using Electro-oculogram

Summary

The article describes a practical method for recording horizontal eye movements with high accuracy by electro-oculogram in neurological patients, using a cup Ag-AgCl electrode with a wide plastic fringe. Stable measurement requires proper selection and fixation of electrodes, taking sufficient time for light adaptation to occur, and re-calibration as needed.

Abstract

Electro-oculogram (EOG) has been widely used for clinical eye movement recording, especially horizontal saccades, although the video-oculography (VOG) has largely taken the place of it nowadays due to its higher spatial accuracy. However, there are situations in which EOG has clear advantages over VOG, e.g., subjects with narrow eye clefts or having cataract lenses, and patients with movement disorders. The present article shows that if properly implemented, EOG can achieve an accuracy almost as good as VOG with substantial stability for recording, while circumventing problems associated with VOG recording. The present paper describes a practical method for recording horizontal saccades using oculomotor paradigms with high accuracy and stability by EOG in neurological patients. The necessary measures are to use an Ag-AgCl electrode with a wide plastic fringe capable of reducing noise, and to wait for sufficient light adaptation to occur. This waiting period also helps to lower the impedance between the electrodes and the skin, thereby ensuring stable signal recorded as time goes by. Furthermore, re-calibration is performed as needed during the task performance. Using this method, the experimenter can avoid drifts of signals, as well as contamination of artifacts or noise from the electromyogram and electroencephalogram, and can collect sufficient data for clinical evaluation of saccades. Thus when implemented, EOG can still be a method of high practicability that can be widely applied to neurological patients, but may be effective also for studies in normal subjects.

Introduction

There are three major ways to record eye movements, the conventional EOG, the VOG recorded by the video-based eye tracking system, and the scleral search coil (SSC) method. Among them, EOG has been frequently used for recording eye movements in patients since the 1970s because of its simplicity. Widely applicable to the clinical population, this method has been extensively utilized for the diagnosis of neurological patients and has provided useful information about the pathophysiology underlying the disorders^1,2,3,4,

Protocol

All experimental procedures in this study were approved and conducted according to the guidelines of the institution's human research ethics committee after obtaining informed consent.

1. Prepare the Subject and the Room for Recoding

1. Perform recording in a room with low ambient illumination, to allow sufficient light adaptation.
2. Have subjects sit in front of a black, concave dome-shaped screen measuring 90-cm in diameter that contains light-emitting diodes (LEDs) embedded in pinholes, which serve as the fixation points and saccade targets used for the oculomotor paradigms.
   NOTE: The LEDs are arranged in hori....

Results

Figure 2 shows representative simultaneous records of EOG and VOG in a normal subject. 8 trials of VGS are superimposed for EOG (gray curves) and VOG (red curves; Figure 2A). Calibrated by the present method, EOG and VOG data are known to be linear over a range of 5-30 degrees, and the spatial accuracy of the data is 0.5 degrees.

The records obtain.......

Discussion

Although nowadays, the prevailing method for recording saccades has become the VOG, the present study showed that EOG can achieve an accuracy almost comparable to that of VOG if properly implemented (Figure 2). The present EOG method has been shown to achieve a good correlation with VOG when recording horizontal saccades and has been successfully used in many previous studies by the same group^12,13,14

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Electrode	Nihon-Kohden (Tokyo, Japan)	NS111-115	cup electrode
Electrode paste	Nihon-Kohden (Tokyo, Japan)	Gelaid Z-101BA	gel electrode paste to fill in the cup electrode
Adhesive tape	Nihon-Kohden (Tokyo, Japan)	H261	double-stick tape for fixating the electrode
DC-amplifier	Nihon-Kohden (Tokyo, Japan)	AN-601G	amplifier for EOG
video-based eye tracking system	SR research (Mississauga, Ontario, Canada)	Eyelink II	eye tracking system for recording VOG
Filter	NF corporation	MS-521	filter for the EOG signal