Modal views completely capture the user’s attention until a task is complete. iOS clarifies this to users by dimming and disabling all other content when a modal view, such as an alert or popover, is visible. An app that implements a custom modal interface needs to hint to VoiceOver that this view deserve the user’s undivided attention by setting
accessibilityViewIsModal. Note that this property should only be set on the view containing modal content, not elements contained within a modal view.
myModalView.accessibilityViewIsModal = YES;
Tagging a view as modal encourages VoiceOver to ignore sibling views. If, after setting this property, you find that VoiceOver still navigates other elements in your app, try hiding problem views until the modal dismisses.