Office Online works in a web browser. This makes its accessibility features work a little differently than Office desktop programs. For example, keyboard shortcuts might not be the same and the page layouts are different. However, all the keyboard shortcuts and other accessibility features that you know from the browser work in Office Online. You can also use the browser controls to zoom, to change text size, and to control screen colors.
Office Online provides WAI-ARIA support for assistive technologies (WAI-ARIA stands for Web Accessibility Initiative-Accessible Rich Internet Applications). If you use an assistive technology such as a screen reader or speech recognition software, you will have the best experience in Office Online if the assistive technology that you use supports WAI-ARIA.
Note: VoiceOver users on the Mac OS X platform may experience mixed results in accessibility depending on the web browser being used. The Safari web browser is recommended for Office 365 Online.
Microsoft Accessibility Documentation
Microsoft provides additional help for accessibility needs. Please go here for additional assistance: http://support.microsoft.com/gp/contact-microsoft-accessibility
Additional Help or Questions about Accessibility