When rendering out a
scene with a stereoscopic camera, Maya renders out the individual
left and right camera images. The images have to be composited in
order to apply the desired stereo effect.
Open the Render View window by selecting Window
> Rendering Editors > Render View.
In the Render View window
select Render > Render ><exampleCamera.exampleCamera>
You have now selected
your stereo camera for rendering
To view your render output in other stereo
modes select Display > Stereo Display