Copyright and accessibility is a complicated topic. Many institutions of higher education have legal and moral obligations to provide all students and researchers with an equal opportunity to participate in and benefit from access to materials. But there is no formal exception in copyright law written for accessibility. 
The law defines accessibility as the ability for people with disabilities to access information resources using technology effectively and efficiently. The principles of accessibility require materials to follow the acronym POUR: perceivable, operable, understandable, and robust. Digital accessibility is making information and services such as documents, websites and web applications, mobile and desktop applications, and audio/video files usable to the widest audience as possible.
One exception that users can often rely on is Section 1201 of the Digital Millennium Copyright Act, which prohibits the circumvention of technological protection measures placed on a work. The law provides exemptions to the anti-circumvention rule that are examined every three years, including some for accessibility.
Fair use is one of the most common exceptions used for accessibility. Examples such as adding captions to an audiovisual work or reproducing text to make it accessible or useable by a screen-reader, are common use cases that rely on fair use. While fair use can significantly strengthen a fair use argument, it is only one factor, and does not automatically make something a fair use.