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Choosing a system


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Noone has an in-depth knowledge of all the current eye movement monitoring technologies and the choice of the most suitable system is thus a difficult one. Fortunately, despite the bewildering array of manufacturers, the number of suitable systems is normally narrowed down to a handful by the individual's own requirements or restrictions. The individual can then contact those manufacturers directly in order to obtain more detailed information with which to make their final decision. This is the purpose of the Eye Movement Equipment Database.

Principal in reducing the selection of suitable systems are the following criteria (in no particular order):

Accuracy (temporal and spatial)

There are, of course, limits to the spatial accuracy of systems. Video Oculography (VOG), Purkinje reflection, or scleral coil systems have the edge in this area, typically with accuracy of greater than 0.5 degree in both horizontal and vertical directions. Infrared Oculography (IROG) using limbus tracking is less accurate (? degree), particularly in the vertical direction, but is often the preferred option if high temporal accuracy is required (typically greater than ?Khz), though VOG systems with high temporal resolution exist. The difficulty with electrooculography (EOG) is that it tends to be prone to generating drift which makes the spatial localization of point of gaze problematic. It is also sensitive to facial muscle activity and electrical interference. However, if recording saccadic latency or simply whether a saccade took place and its direction, then spatial accuracy may have very little bearing on the choice of equipment at all, and IROG or EOG may be perfectly adequate.

Suitability for operational conditions

The conditions under which the system is operated will play a large part in determining which system is most suitable. For example:

  • Head-free operation: Is it necessary that the equipment be attached to the head or to operate remotely? Will it matter if the head is immobilised or free to move, and if the latter, will the system have to adjust for head movements? Some subjects (for example the infirm or babies) might object or find it too uncomfortable to have their head clamped into equipment. Additionally if the equipment is required for use in real-world situations or to simulate those conditions, it may be necessary that it is as unobtrusive as possible.
  • Place of operation: Will the equipment be mounted in a car or some other isolated or inaccessible place? Does it need to transmit data to some remote receiver, or record it to tape for later examination? Will it need to be of low power consumption, or powered by batteries?
  • MRI scanning: Will eye movements be measured during an MRI scan? If yes, it will be necessary to minimise the amount of metal used in the construction of the equipment.
  • Obstructions: Will spectacles, helmets or head-mounted displays be worn by the subjects? Will these restrict the positioning of the eye monitoring equipment? This may be a problem with some of the bulkier video methods, less so with IROG methods.
  • Duration of recording: How long will the subject have to wear the device? The discomfort of scleral coil methods limits subjects to around 1/2 hour sessions. Other systems may impose restrictions on the duration of recording due to the data storage limitations of the equipment.


Fortunately, cost is not an indicator of suitability for purpose, and it is quite possible to pay a lot and get a less useful piece of equipment than one which would have been cheaper and simpler. However, budgets are (nearly always) limited to some degree, and cost will certainly have a part to play in the final decision.

As a general rule of thumb, at 2000 prices and in US dollars:

  • Electrooculography (EOG) USD ?
  • Infra Red Oculography (IROG) USD 10,000-30,000
  • Video Oculography USD 10,000-100,000
  • Scleral Coil USD 10,000

This document was originally compiled by our colleague, the late Dr. David Wooding,


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