Edited Lime Survey template in order to use the GazeCloudAPI (https://gazerecorder.com/gazecloudapi/) library to save eyetracking data from users while taking a survey. Unfortunately, for now the demo has a time limit of 60s.
Download the files, put them in a folder and copy it in path-to-file...\LimeSurvey\themes\survey
From the LimeSurvey theme editor (https://site-name.limesurvey.net/admin/themeoptions), press on "install". After that you can use it as a template when creating a survey.
Todo: save eye-tracking data retrieved by the library and generate a heatmap.