how is it formed?
In a tropical cyclone  ,the eye is formed when air begins to descend in the center of the storm creating a mostly rain-free area.
Eye (cyclone)
However, a small portion of the built-up air, instead of flowing outward, flows inward towards the center of the storm. This causes air pressure to build even further, to the point where the weight of the air counteracts the strength of the updrafts in the center of the storm. Air begins to descend in the center of the storm, creating a mostly rain-free area—a newly formed eye.

is there oxygen in the eye of a tornado UNANSWERABLE what is meant by the eye of a cyclone? It  is a region of mostly calm weather at the center of strong tropical cyclones. how is it structured? A typical tropical cyclone will have an eye of approximately 30–65 km (20–40 mi) across, usually situated at the geometric center of the storm. The eye may be clear or have spotty low clouds (a "clear eye"), it may be filled with low- and mid-level clouds (a "filled eye"), or it may be obscured by the central dense overcast. what kind of effect does it have? The "stadium effect" . what do you mean by this term? It is an event where the clouds of the eyewall curve outward from the surface with height. This gives the eye an appearance resembling an open dome from the air, akin to a sports stadium.
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Eye (cyclone) [SEP] Formation and detection
There are many aspects of this process which remain a mystery. Scientists do not know why a ring of convection forms around the center of circulation instead of on top of it, or why the upper-level anticyclone only ejects a portion of the excess air above the storm. Many theories exist as to the exact process by which the eye forms: all that is known for sure is that the eye is necessary for tropical cyclones to achieve high wind speeds.