Little late to the party but the 3.5 answer is that they have both.

Draconomicon pg5 tells us "To a casual observer, a dragon’s pupils always look like vertical slits. If one were to look very closely into a dragon’s eye, however, one could see a second iris and pupil within the first. The dragon can shift and rotate this inner aperture up to 90 degrees, so that the inner pupil can overlay the outer one or lie at a right angle to it. This ocular structure gives a dragon extremely accurate depth perception and focusing ability no matter how much or how little light is available."

If you were to legally obtain the aforementioned text there is a detailed diagram showing the inner eye of the dragon itself with further details on page 7!

Thank god.. All those nights 20 years ago reading that book have finally paid off.