Accessible presentations should limit transitions whenever possible. When a PowerPoint presentation is converted into a Adobe Presenter 9 presentation, transitions force the user to press the Play button to advance through each transition. This can result in a time-consuming and tedious experience for screen reader users.
Consider the example of a slide containing bullet points which fly in from the right: as each bullet transitions onto the screen, a screen reader will return to the top of the page and recommence reading the page’s contents from the beginning. To advance to the next bullet, the user will need to press the Play button. This can create a frustrating experience for the screen reader user. While it may be acceptable to occasionally use transitions, they should not be used on every slide. Limiting the use of transitions and animation to one per slide will help to improve the usability of your presentation for screen reader users.
If you must use Animations in your PowerPoint presentations then these should be made accessible. Ensure that Flash animations used in your presentations are accessible by following the recommendations for accessible Flash authoring at the Adobe Accessibility Resource Center.
In addition, you should carefully consider your use of decorative animations. Constant motion on the screen may cause a screen reader to refresh frequently, thus making the presentation more difficult to use. Keeping animations to a minimum or eliminating them altogether will increase the accessibility of your content.