The eye of a tornado, like the eye of a hurricane, is merely the center of the funnel.
In 1928, a Kansas man by the name of Will Keller flattened himself to the ground as a tornado skipped over him. He watched the tornado as it passed over him, and what he saw added invaluable information to our knowledge of the insides of tornadoes.
In the few seconds it took for the tornado to pass, the air became strangely calm. Keller had difficulty breathing and heard a noise he described as a screaming, hissing sound coming from the funnel. The funnel opening above him was about 55 feet (17 meters) across and extended some 2,500 feet (762 meters) up.
Toward the bottom of the tornado, Keller saw a number of small tornadoes form and dissipate. It would have been impossible to see anything because of the darkness except for constant bright flashes of lightning ricocheting off the interior walls of rotating wind and debris.
While pilots can fly airplanes through the eye of a hurricane—and they do, to study the phenomenon—tornadoes are too small, too spontaneous, and exist for too brief a time for close observation of the eye.