The long term answer is the Accessibility Object Model spec currently under development.
The current answer is to build a replica DOM structure for accessibility purposes.
• keyboard support (being able to navigate to all controls as needed, not being stuck in a navigation island from which there is no escape with the keyboard, etc.)
• pointing device considerations (not requiring drag unless absolutely essential, no action on mouse-down, etc.)
• not requiring the simultaneous use of mouse and keyboard (e.g. via modifier keys)
• sufficient size for buttons and other pointer targets
• the ability to suppress animations, flashing images, etc.
• the ability to control colors and contrast of things on the screen
...
Of course, something like Photoshop, Illustrator, or the visual part of Google Maps is hard to use when you cannot see, but there are so many different disabilities that some or even most accessibility guidelines can apply to pretty much any software.