Microsoft PowerPoint has a built in accessibility tools to assist in making your slides compliant. As with other formats, you will need to ensure that the structure is consistent and hierarchical, tables have the proper structure and are not images, and that all figures have appropriate alternate text.
The website WebAIM generally addresses website accessibility, however it does give a great overview of accessibility for the program Microsoft PowerPoint.
Microsoft PowerPoint is an image rich program intended to build eye catching slides which often incorporate images of all kinds. PowerPoint can include design factors that may not seem like images such as colorful backgrounds. All images need to be defined by Alternate text. Alternate text should only be a sentence or two long, and should describe what is important about the image. Think carefully about what you are trying to convey in an image rather than trying to describe every element. Three things to remember when making images accessible in PowerPoint.
ALL images require either alternate text or designation as a 'decorative image'
An image should only be marked as 'decorative image' if it serves to visually separate sections, and your content would not be altered by removing it from the slide. Otherwise, give the image meaningful alternate text.
Check each image to ensure junk text isn't in the 'Alternate Text' field and tricking the Accessibility Checker.
Instructions on how to add Alternate Text to images in PowerPoint
Tables in PowerPoint cannot be images. Due to the small spacing issues it can be tempting to take a screen shot and shrink the table until it fits, however, if you use an image of a table none of the data will be accessible. Like other accessible tables, in PowerPoint you will need to ensure that each table has an appropriate Header Row to identify the table to assistive technology. For full instructions, and additional information please see the Accessible Tables in PowerPoint.
Additional information on making tables accessible in PowerPoint.
Ensure that each slide has a unique "Slide Title", most of the standard options for slide structure have a segment to include the slide title. These titles serve as the Headings structure as explained in the Microsoft Word and Adobe PDF tabs. It is important that every slide has a title so that sections aren't skipped and that each slide has a unique title so that users can correctly identify the specific example they need. For example instead of using "References continued" for each subsequent slide of references consider numbering them as "References 1, References 2, etc."
Converting to PDF
If you are converting your PowerPoint slides into another format, such as a PDF, please be aware that some accessibility aspects can transfer messily. For instance, text boxes and slide titles in your slides can be converted to images in the PDF. These accessibility errors will need to be corrected in Adobe.
Additionally, if you have speaker notes in your PowerPoint slides, when you save a file as a PDF you will get the warning "Would you like to convert this presentation's speaker notes to text annotations in the PDF? The annotations will be created on a separate layer that can be toggled on or off." Select "No", as transferring the speaker notes will create accessibility issues.