It must be easy for all users to perceive the information presented to them in a questionnaire. This means ensuring that everyone understands the questions and that everyone, including those with impaired vision, can navigate their way through your survey. This means, among other things, that all "non-text” elements, such as images, graphic elements and any audio and video content, must have a descriptive text, so that it is comprehensible to a screen reader or other assistive technology.
Keep in mind that a very pedagogical illustration of an arrow to click on is not very useful if the respondent cannot see it.
All content must therefore be completely clear to respondents with impaired vision and those with cognitive issues or learning difficulties, by using descriptive text. Thus, every element of your questionnaire can be perceived using technical aids such as screen readers.
It must be possible to answer all questionnaires by using just a mouse or keyboard. It is therefore important that it is always clear where on the page a person is, in order to be able to orientate oneself.
All content in your questionnaire must be so easy to understand that everyone, with or without disability, can understand and follow the instructions without additional guidance. You can ensure this by, among other things, being consistent in the names and descriptions of functions and navigation tools. Being pedagogical is also important in this context. How should the respondents answer the questions? Should they press a particular key? Where should they click to progress when they have answered? Explain everything with simple and easy-to-understand text.