accessible on-line survey

Hello List,

I am assembling an on-line survey for users who have visually 
impairments or who have dyslexia as a part of my Master's thesis.  I 
was wondering if anyone might be familiar with on-line survey software 
that is known for rendering accessible content to subjects who use 
assistive technology, or that facilitates the author of the survey as 
he/she produces accessible content?

Your opinions would be very much appreciated!  Thank you!

Sincerely,
Annmarie Gemma