The eyeball; the spherical part of the eye that contains the structures involved in vision.
ボールが顔に当たり、眼球を痛めた。
A ball hit his face and injured his eyeball.
眼球の検査のために瞳孔を広げる薬を点眼した。
They put eye drops in to dilate the pupils for an eyeball examination.
解剖の授業で動物の眼球を観察した。
In anatomy class we observed an animal's eyeball.