Disadvantages of Eye Tracking

1. The equipment is expensive
2. Some users can't work with the equipment (for example if they wear contact lenses or have long eye lashes)
3. Calibrating the equipment takes time; this problem may resultantly cause the user to deviate from using the device.

Point elaboration -

Point 1 - It’s not cheap to outfit a lab with a decent eyetracker. Even Google, which has all the money in the world, has only outfitted one of their many labs. In addition to the money spent on the equipment, you have to spend money training people how to use it, which is not a cheap proposition.

Point 2 - not every participant can work with an eyetracker. Depending on the hardware, people with a variety of attributes automatically are disqualified from eyetracking. Everything from contact lenses to long eye lashes can get in the way of the device working properly.

Point 3 - Getting a participant set up and calibrated with the device can take time away causing a lack of interest in using the device.

Point 4 - Eye movements, like other passive and non-command inputs are often non-intentional, so they must be interpreted carefully to avoid unwanted responses to user actions. In terms of eye movement, we call this the "Midas Touch" problem. The problem of employing the use of an eye tracker interface is that people are not accustomed to operating devices simply by moving their eyes.

Point 5 - A major disadvantage is that the eye as a computer input device. Moving one's eyes is often an almost subconscious act. Unlike a mouse, it is relatively difficult to control eye position consciously and precisely at all times. Instability is introduced into the output of the eye tracker whenever it fails to obtain an adequate video image of the eye for one or more frames. This could mean that the user blinked or moved his or her head outside the tracked region.

Point 6 - As eye movements are so different from conventional computer inputs, we achieve best results with a philosophy that tries, as much as possible, to use natural eye movements as an implicit input, rather than to train a user to move the eyes in a particular way to operate the system.