EOG

Overview:

The electro-oculogram (EOG) is a recording of eye movements non-invasively using skin surface electrodes placed around the orbit. The technique makes use of a 4-6mV standing voltage potential that exists between the pigmented epithelium at the back of the eye and the cornea at the front, creating a dipole. This is known as the corneo-fundal potential. It was first discovered in 1849 by du Bois-Reymond.

As the eye saccades or otherwise attends to the visual scene the vector of the corneal-fundal potential changes with the visual axis. This can be monitored using bipolar electrodes in two basic configurations: two channel, designed to detect movement onset and direction in a single plane; or four channel, designed to detect movement onset and direction in any plane.

Method:

General concept

The corneo-fundal dipole can be measured using bipolar electrodes to provide information about eye movements, e.g., angular amplitude and velocity:

Schematic representation of the eye and the polarity of the corneo-fundal potential (top). Angular deviation of eye position changes the vector of the dipole, resulting in amplitude changes in the EOG recording.

Electrode placement and preparation

Skin must be prepared prior to electrode placement using mildly abrasive creams and alcohol to remove skin debris and sebaceous oils. Any suitable surface electrode (e.g., Ag-AgCl) may be used. Depending on whether eye movement amplitude and velocity are required in a single axis (e.g., horizontal eye movement only) or dual axes (vertical and horizontal), a two or four channel configuration, respectively, will be required:

Two Channel Configuration
In this configuration, one electrode is placed slightly above the outer canthus of the right eye, whilst the other is placed slightly below the outer canthus of the left eye. Reference electrodes are placed at the contralateral (opposite) ear or mastoid processes. Because eye movements are largely binocularly synchronous in both sleeping and awake subjects, this electrode configuration will provide out-of-phase deflections on each electrode for most types of eye movements.

An illustration of two channel EOG used to detect horizontal eye movements.

Four Channel Configuration
In this configuration electrodes are placed horizontal to the outer canthi as well as infraorbital and supraorbital locations, with all electrodes paired with a similar ear, mastoid or supranasion electrode. The advantage of this technique is that simultaneously recording vertical and horizontal eye movements allows for eye position and vector to be calculated.

Note: Specific information about eye positions requires a DC-coupled recording,(e.g., EOG Pod. Two EOG Pods will be required for recording both vertical and horizontal eye movements.

Amplifier

EOG bioelectrical signals are typically within the mid to upper microvolt range (µV), thus requiring suitable amplification and filtering in order to be recorded. The type of eye moment being recorded from also has implications for the type of amplifier than can be used (AC or DC coupling). For instance, in the case of slow eye movements such as smooth pursuit (<200 degrees/sec in humans), a DC-coupled amplifier is required to preserve lower frequencies (e.g., 0.07 - 1.7 Hz). For fast saccadic movements (200-600 degrees/sec in humans; e.g., up to 10 Hz) either a DC or AC coupled amplifier may be used.

ADInstruments offer a range of Bio Amplifiers that when connected to a PowerLab data acquisition unit are certified safe for use with humans or used with animals. These bioamplifiers are fully software-controlled using LabChart or Scope.

Note: If an AC coupled amplifier (e.g., Bio Amp) is used to record smooth pursuit movements, eye movement velocities < approx. 100 degrees/sec may contain artifacts; while eye movement velocities significantly less that 100 degrees/sec will not be visible at all. For smooth pursuit recordings an EOG Pod is recommended.

Data Analysis

Assuming a DC-coupled amplifier is used, the phase of raw eye movement signals will consistently relate to deviation of the corneo-fundal potential with respect to the recording electrodes. Thus, a suitable conversion factor from mV to eye movement amplitude (degrees) may be used. In LabChart this can applied using Units Conversion. Similarly, to obtain eye movement velocity the derivative of the amplitude signal can be applied. In order to gather statistics of peak amplitudes and peak velocities etc, the LabChart module Peak Analysis may be used.

Software:

The LabChart Advantage:

(may require additional Modules and Extensions)

  • LabChart data files can be marked with events using the Comments feature
  • Units Conversion can be applied to EOG data to obtain amplitude in degrees
  • Differentiation can be applied to amplitude signal to convert to EOG velocity (°/sec)
  • Use Cyclic Measurements feature for studies of nystagmous
  • Analyze peaks in amplitude or velocity waveforms using the Peak Analysis Module
  • Macros can automate many tedious and repetitive analysis tasks
  • Automated extraction of data from recordings using online Timed Add to Data Pad or offline using Multiple Add to Data Pad
  • Extracted parameters in the Data Pad can be easily exported for further analysis, e.g in Excel or Matlab

LabChart

LabChart software (for Windows and Macintosh) together with a PowerLab data acquisition system offers up to 32 channels of real-time data acquisition, data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Additional acquisition and analysis functionality is provided with the use of specialized LabChart Extensions and LabChart Modules. Modules are available as part of LabChart Pro while Extensions are free for download from the website for existing LabChart users. 


Example 2-Ch recording of horizontal saccades

Peak Analysis Module

The Peak Analysis Module (Windows) provides automatic detection and analysis of multiple, but not overlapping, signal peaks in acquired waveforms.

It provides:

  • Real-time or offline analysis
  • Fast parameter extraction and analysis from single or multiple peaks
  • Automatic peak detection of an entire channel or a selection within a channel
  • Detection of positive or negative peaks
  • Provides several analysis presets suitable for general and specific types of waveforms
    • Evoked Response, Population Spike, Synaptic, Action Potential and Cardiac Action Potential
  • Instant tabulation of extracted parameters that can be exported to other applications
    • Height, width, area of the peak and time to peak

The Peak Analysis Module can be used on calibrated EOG data to obtain a number of statistics, e.g.: 

  • Average amplitude/velocity of saccadic eye movements
  • Time to saccade
  • Time to reverse saccade
  • Duration of complete saccade cycles

GLP and 21 CFR Part 11

For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance the GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the Good Laboratory Practice application page or contact your nearest ADInstruments representative.

Hardware:

PowerLab Data Acquisition Systems

The PowerLab is a high-performance data acquisition unit capable of recording at speeds of up to 400,000 samples per second continuously to disk (aggregate). PowerLab units are compatible with instruments, signal conditioners and transducers supplied by ADInstruments, as well as many other third-party companies. In addition to standard single-ended BNC inputs, 4 differential Pod ports are also available for direct connection of Pod signal conditioners and appropriate transducers. Research PowerLab units include:

Signal Conditioners

Human EOG

The following ADInstruments' biological amplifiers are independently certified to comply with international safety standards and are fully isolated for connection to human subjects:

FE132 Bio Amp

FE135 Dual Bio Amp


ML408 Dual Bio Amp/Stimulator


Note: The Bio Amp, Dual Bio Amp and Dual Bio Amp/Stimulator are manufactured for use with PowerLab data acquisition systems and are fully software-controlled by LabChart or Scope. These Bio Amps cannot be used for recording 3 or more biopotentials on a single subject; however, they may be used for multiple subjects that have separate grounding leads. For recording more than 3 biopotentials from a single subject see below:

Multiple-Channel EOG Recordings

ADInstruments also provides multiple channel bioamplifiers that connect directly to PowerLab data acquisition systems. These units are also fully-isolated, and independently certified, for connection to human subjects.

ML138 Octal Bio Amp

  • A differential amplifier that consists of eight electrically isolated differential input AC amplifiers
  • A shared ground connection across all eight inputs.
  • Supplied with two packets of MLA0310 Lead Wires (1.8 m, 10 snap on)


GT201/F 16 Channel Bio Amp


ML317 EOG Pod

 

Animal EOG

The following ADInstruments' biological amplifiers for use with animals (i.e. pithed toad, or anaesthetized rat/mouse) only:

FE136 Animal Bio Amp

Accessories

Bio Amp cables:


Leads compatible with both shielded (MLA2340 & MLA2540) and unshielded (MLA1340 & MLA1540) cables:


Leads compatible with shielded cables (MLA2340 & MLA2540) only:


Leads that directly connect to the Dual Bio Amp


Leads that directly connect to the Animal Bio Amp


Electrodes:


Consumables:

Maturation of the initial ventilatory response to hypoxia in sleeping infants
Richardson H.L, Parslow P.M, Walker A.M, Harding R and Horne R.S.C., Journal of Sleep Research, 117-127, 2007

Activation of 5-HT1A receptors in medullary raphe disrupts sleep and decreases shivering during cooling in the conscious piglet
Brown J W, Sirlin E A, Benoit A M, Hoffman J M, Darnall R A, American Journal of Physiology: Regulatory, Integrative and Comparative Physiology, R884–R894, 2008

Can Bile Acids Function as a Migratory Pheromone in Banded Kokopu, Galaxias Fasciatus (Gray)?
Baker C.F, Carton A.G, Fine J.M, Sorensen P.W., Ecology of Freshwater Fish, 275-283, 2006

Citations Database


The material on this page is provided in good faith and believed accurate at the time of writing. No responsibility will be taken, or liability accepted, for damages arising from the use of information herein. Readers are urged to check with respective manufacturers the accuracy of all product related information.

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