It is hard to design a lesson that works for all disabilities, especially for an online-only course. For an in-person class, a teacher can accommodate for students will disabilities by proving them with handouts and individualized instruction. Students who participate in online learning can have varied disabilities, and providing them with technology accommodations, like closed captioning, text-to-speech, and other features, can be difficult to find a component online that contains all of the possible accommodations if do not create it yourself.
I have taken two American Sign Language courses. I not only learning the language, but I also learned Deaf History and accommodations that can be made for the deaf. For an online course, typically the only accommodation that the deaf need are closed captioning. After these courses, I am very sensitive to the issues the disabled face with day-to-day activities, like going to school.