We have experienced similar difficulties as well as with some contact lenses. I think the issue is that there is a difference in how the natural lens of the eye and  other lenses refract light. We often had problems with individuals with significant astigmatism .
The eye trackers use one or two algorithms. The bright pupil algorithm uses the double purkinje image that bounces the systems IR off the retina; so small differences in refraction could cause problems. The dark pupil algorithm is less accurate but doesn't use the double purkinje image. Tobii's eye trackers use both algorithms.
In some cases, I got some improvement by using a single eye rather than both eyes.
Hope this helps.

Richard Hurtig, PhD,
ASHA Fellow
Professor Emeritus
Department of Communication Sciences & Disorders
The University of Iowa

President & CSO
Voxello, Inc.
www.voxello.com
Sent from my iPhone

> On Oct 1, 2015, at 3:56 PM, Rachell Westby <xxxxxx@alsinfo.org> wrote:
>
> Just another thought...I've also noticed a big difference for some with the different versions of Tobii for example those who couldn't calibrate to the C series due to eye conditions were able to with the I series.  They often update their eye tracking hardware with the release of new devices.  If you do not have an I series plus, the latest from Tobii-DynaVox, you might want to try it to see if there is any difference.
>
> Also, trying the Quha Zono Mouse ( http://www.graspat.com/ ) in the place of a traditional headtracker, might be something to try.  It offers more range with less movement, has greater flexibility with positioning, and can be used on many parts of the body.  It works with computers and android tablets such as Samsung.  I've seen it work with both T-10/T-15 and the I series device.
>
> Best Regards,
>
>
> Rachell Westby, M.C.D., CCC-SLP | Assistive Technology Specialist
> The ALS Association - DC/MD/VA Chapter
> 2800 N. Parham Road Suite 208| Richmond, VA 23294
> T:866.348.3257 ext. 103|C: 804.912.5758|F: 804.836.1751
> E: xxxxxx@alsinfo.org | ALSInfo.org
>
>
>
>
> Join us this fall as we Walk to Defeat ALS! For more information or to register, please visit www.WalktoDefeatALS.org
>
>
> -----Original Message-----
> From: xxxxxx@alsa.simplelists.com [mailto:xxxxxx@alsa.simplelists.com] On Behalf Of Lisa Bruening
> Sent: Thursday, October 01, 2015 3:46 PM
> To: xxxxxx@alsa.simplelists.com
> Subject: Re: Lens implants
>
> So far my dynavox eye max and Tobii have not been  reliable options...
>
> She has some head movement and is using Margaret's low tech laser with great results, so we will try tracker pro but if she loses head control, we won't have any eye gaze adaptation.
>
> Just wondered if others had same issues as it might change recommendations.
>
> Thanks for the real time feedback!
>
> Sent from my iPhone
>
>> On Oct 1, 2015, at 3:23 PM, Rachell Westby <xxxxxx@alsinfo.org> wrote:
>>
>> Initially I would say both Tobii-DynaVox I Series devices and LC Technology's EyeGaze Edge are great to consider, because I have seen the most results with them as far as different eye conditions go.  However, on the flip side of this... I have also worked with someone who had similar eye surgery and afterwards could no longer use their eye gaze device (Tobii I 15 ) when he using it perfectly before.  He ended up getting the NeuroSwitch (http://www.controlbionics.com/)  device and has been really successful.   I think eye surgeries/conditions affect people's ability to use eye gaze technology differently, as in it is different for each person even if they have the same condition.  Unfortunately no one company can say that their technology will not be affected by eye conditions, because there is always an exception.  So if the patient with an eye condition is a veteran or can afford to pay for their own device the NeuroSwitch is a good option to consider along  with the other options (currently not fundable by insurance).  When evaluating someone with an eye condition for eye gaze, I try to get my hands on each product to try with the person, because you never know what might be the best fit until they try it out.
>>
>>
>> Best Regards,
>>
>>
>> Rachell Westby, M.C.D., CCC-SLP | Assistive Technology Specialist The
>> ALS Association - DC/MD/VA Chapter
>> 2800 N. Parham Road Suite 208| Richmond, VA 23294
>> T:866.348.3257 ext. 103|C: 804.912.5758|F: 804.836.1751
>> E: xxxxxx@alsinfo.org | ALSInfo.org
>>
>>
>>
>>
>> Join us this fall as we Walk to Defeat ALS! For more information or to
>> register, please visit www.WalktoDefeatALS.org
>>
>>
>> -----Original Message-----
>> From: xxxxxx@alsa.simplelists.com
>> [mailto:xxxxxx@alsa.simplelists.com] On Behalf Of Margaret Cotts
>> Sent: Thursday, October 01, 2015 3:04 PM
>> To: xxxxxx@alsa.simplelists.com
>> Subject: RE: Lens implants
>>
>> Hi Lisa-
>>
>> Years ago I had a client who was using eye gaze (QuickGlance, I
>> think).  He was using it pretty well... He had a lens implants after
>> corneal surgery, and afterwards he couldn't use his eye gaze system at
>> all... (We tried an LC Technologies system, but he couldn't use that
>> either...)
>>
>> I couldn't speak to what systems might work better, but I just wanted to put that out there...
>>
>> Margaret Cotts
>> Low Tech Solutions
>>
>> -----Original Message-----
>> From: xxxxxx@alsa.simplelists.com
>> [mailto:xxxxxx@alsa.simplelists.com] On Behalf Of Lisa Bruening
>> Sent: Thursday, October 01, 2015 11:50 AM
>> To: xxxxxx@alsa.simplelists.com
>> Subject: Lens implants
>>
>> Hi,
>>
>> Has anyone used eye gaze control with a person who has lens implants after cataract removal?
>>
>> If so, was there a device that worked better?
>>
>> Sent from my iPhone=
>>