Sneak Peak: Accessibility in Office Web Apps

Microsoft Office Web Apps allows you to access and edit files online in your web browser. Office Web Apps include a number of accessibility features. Office Web Apps provide screen reader support, keyboard accessibility, and high contrast modes.

Support for assistive technology products.

The Word Web App and PowerPoint Web App have display modes that make them accessible to screen readers. If you use assistive technologies, such as a screen reader or speech recognition software, you will have the best experience in Office Web Apps if the assistive technology that you use supports WAI-ARIA. Office Web Apps provide WAI-ARIA support for assistive technologies (WAI-ARIA stands for Web Accessibility Initiative-Accessible Rich Internet Applications).

Use familiar keyboard shortcuts from the Office desktop applications that also work in Office Web Apps.
Use accessibility features in your web browser to improve accessibility of Office Web Apps. Office Web Apps run in a web browser so you can use your web browser’s accessibility features to improve the readability and accessibility of Office Web Apps.

Source: http://www.nhsocal.com/ResourceCenter/Blog/TabId/2847/artmid/18966/articleid/1734/Default.aspx