Fitting A Mount Kit – Part 3: Eye-gaze Access

When mounting an eye gaze device, the fitting of the mounting system is crucial to ensure consistent and accurate positioning of the device, which is required by the access method employed.

As with all mounting you will require a tape measure and simple tool kit for assembly (all tools are supplied in every mount kit however you can never be over-prepared!) and if possible a second pair of hands or a floor-standing Rolling Mount or Desk Mount, particularly for eye gaze mounting as we will attempt to work backwards from the “In-Use” position of the mounted technology.

The Steps to Consider

If you have read our last article in this series (Fitting A Mount Kit – Part 1: Frame Clamps), you would now have an idea of how to identify and fit the most appropriate Frame Clamp to suit your wheelchair.

The Frame Clamp is the first step and starting point for ALL wheelchair mounting actions, including when looking at attaching and positioning eye-gaze access technologies.

Once the Frame Clamp has been considered, you now have the anchor point for the rest of the mounting system.

Here’s what’s next.

Decide on the most appropriate mounting system.

This sounds simple enough but is consist of quite a lot of thought, clinical reasoning, discussion and consultation with the person using the technology and their immediate carers, educators and family.

As with all Assistive Technology provisioning, this is dependent on a variety of factors including:

  1. A person’s abilities and needs.

    This may include people who use more than one access method to their device or a person with a degenerative condition who may be initially accessing a device directly but likely to be using eye gaze in the future. In these cases, a height adjustable system may need to be considered.

  2. The type of device to be mounted.

    A heavy device on a long lever arm required for eye gaze will require a more heavy duty mount.

  3. Features of the wheelchair

    For example, is there a tray or controller that the mount needs to be positioned around?

  4. The functionality of the mount

    Does the mount need to be swung to the side or folded to the side for transfers or when not in use or does it need to be compact for storage or transport?

  5. Environmental factors.

    Are there multiple carers involved in using the mount? In this case would be the simplest option to ensure an easy set up.

    Feel free to contact Communicate AT to discuss your options further if needed!

    Once the mount kit is identified, the key to success with eye-gaze mounting resides with how the selected Mounting solution presents the technology as, with eye-gaze access, the relationship between where the device is held and the person using the technology is unique and important.

Eye-gaze Access Technology Positioning

We define the “In-Use” position of mounted technology to be that place in space, generally in front of a person, where the technology is held in the right place for access to it to be at its best.

Other positions include “Egress” (where the device is in a momentary position out of the way so that it doesn’t impede on transfers in/out of the chair or simply just clears the front of the chair for other day to day matters like watching TV, face-to-face communication or any other reason) or “Stowed” (where the device is in a position safe for when the wheelchair is in motion). Basically, these are positions of the mounted technology that are not in the “In Use” position.

Work Backwards from the “In Use” Position

The “In Use” position of eye-gaze access technologies is VERY important. Eye-tracking technologies uses quite specific points of information which is gathered by a camera or cameras looking at certain aspects of the person’s eye.

(Source: Tobii-Dynavox i-13/i-16 Quick Start Manual)

As the person’s gaze moves around a screen, those aspects change and the algorithms used by the cameras convert these changes into on-screen cursor movement. Quite simple when said that way, but there’s a lot more to it behind the scenes.

If you’d like to know more about how that works, here’s a link to the Tobii-Dynavox website, they have a pretty good video outlining it all – How does eye tracking work? – Tobii Dynavox

One specification required of most eye-gaze technologies is the positioning of the device, moreover, the camera itself. Like all cameras, eye-tracking cameras have a focal length.

In general terms, that distance is often between 50cm and 60cm from the person using the technology. And that’s where the mount kit feeds in, it has to hold the technology in that positioning – with repeatability, reliably and with the ruggedness to cope with anywhere the chair will travel.

For mounting the device and fitting the Mount Kit, you need to work out that “In Use” position and WORK BACKWARDS from there. Here’s how …

Working Out Your Measurements

Using Diagram 1: Eye-Gaze Pythagoras below, the end goal is to calculate the distance of measurement ‘C’ – which will equate to the length of the vertical tubing of our mount kit. You can work it out by directly measuring “C” OR you can use the easier measurements of “A” and “B” and then apply Pythagoras’ Theorem – remember in High School when you said “But sir! I’ll never have to use that in the real world!”

A2 + B2 = C2

Don’t worry about it too much, we can work out C for you if you have A and B measured.

The best way to do so is to either hold the device in the optimal position for use OR use a Rolling Mount or Vertical Desk Stand to keep the eye-gaze technology in position whilst you measure.

Take measurements from the Frame Clamp to the middle of the mounting plate on the back of the device. Generally, eye gaze devices sit approximately 60cm from a person’s eyes though this can vary a little between devices and needs to be checked on the monitor on the person’s device.

Diagram 1: Eye-gaze Pythagoras

First used in the DAESSY mounting systems over 35 years ago, mount kits such as the DAESSY Folding Mount or DAESSY Rigid Mount have S-shaped, offset vertical tubing.  The offset in the tube allows the final end point of the tube, the point where the horizontal tubing attached, so be forward of the Frame Clamp attachment point without using as much tube angle as one that is simply straight. In that way, we can manage the effect of gravity better, a force that is always working against us but is tempered by mounting the vertical tube as upright as possible.

Offset bend allows this angle to be softened but is also the simplest of fitting tools where a simple twist around the vertical axis of the bottom section of the tube can navigate the top section of the tube around the edge of a tray or a wheelchair controller. A very handy and very cost effective fitting option.

We’ve outlined how Fine Tuning your mount can be as simple as a few well placed parts in our Article Fitting A Mount Kit – Part 2: Parts for Fine Tuning – Communicate AT Mounting, be sure to check that out as part of your homework into eye-gaze mounting too.

Offset can also be used to set an eye-gaze device position well in front of the person using it and as mentioned above, this can be crucial for eye-gaze technology to work at its best.

Distance ‘A’ will assist in determining the amount of offset in the vertical tubing that may be required.  Generally the offset can be 3″ (standard offset in standard DAESSY Kits), 6″ (standard offset in DAEDSSY Mini kits) or 9″ upon request. No offset is simply a straight tube.

Special considerations for long vertical tube lengths and heavy eye gaze devices.

Due to the increased pressures heavier eye-gaze devices place on a long lever arm and its associated components, it is recommended that for vertical tube lengths greater than 32 inches, additional components could be considered as well.

These are called DAESSY Angle-Lock components. These parts work differently than the regular DAESSY components as they don’t rely on pressure over surface area. Instead, the have large “teeth” or “cogs” that lock into each other and prevent any movement of your eye gaze mount at all around a central point. This is both advantageous but also has it’s disadvantages, we suggest reading our Article Strengthen Your DAESSY Frame Clamp Assembly – Angle-Lock Parts – Communicate AT Mounting to find out more. For certain lengths of vertical tubing for certain heavier technologies, they should certainly be on the “Fitting” radar.

Get It On, Fit It Right, Make It Tight

Once your mount has been assembled, it’s time to attach it to the wheelchair in the optimal position for eye-gaze.  It is recommended that you don’t fully tighten the bolts on the Frame Clamp Assembly and Quick Release Base until you have the correct position as worked out, as per the methodology above.

If another person can assist with positioning it makes the process a lot easier!  Ask the person assisting you to hold the device in the optimal position for use or use your Rolling Mount or Vertical Desk Stand, then you can adjust the angle and height of the mount to suit. The trick to this is to tighten the bolts on the moveable parts of the mount using the tools supplied such that it stays in place under it’s own weight (device not attached as yet) but can still be nudged around with a little bit of force.

If you’re doing this with the device attached, never let go of it at anytime! They are expensive technologies and are precious, protect them from accident when fitting them during mounting.

Once the “In Use” position is established, tighten the Frame Clamp Assembly and then position the Quick Release Base at the right height and angle. Tighten this too when in the right position.  It’s then time to attach the device and make small adjustments if needed.


We hope that this information helps setting up your eye gaze mounting system that will optimally position a person’s eye-gaze system for use.  If you would like further guidance please don’t hesitate to contact Communicate AT.