It is the colored part of the eye that controls the amount of light.
{"18.791_33.5593":[{"id":40988198,"answer":"Eyelids","x":18.791,"y":33.5593},{"id":40988199,"answer":"Pupil","x":18.791,"y":33.5593},{"id":40988200,"answer":"Iris","x":18.791,"y":33.5593},{"id":40988201,"answer":"Eyebrows","x":18.791,"y":33.5593},{"id":40988202,"answer":"Sclera","x":18.791,"y":33.5593}]}
Drag the answer into the correct orange point.