Example sentences
yǎn眼jīng睛yǒu有diǎn点lèi累。
My eyes are a bit tired.
tā她yǎn眼jīng睛zhēn真dà大。
Her eyes are so big.
About this word
眼 and 睛 both mean eye. 眼 is the organ, the everyday working word, and 睛 is the eyeball, the dark center of it. Chinese doubled them into one word the way it did with 身体 and 事情, and 睛 lost its tone in the process: it is yǎnjing, not yǎnjīng. Outside 眼睛 the character 睛 barely appears, though it survives in the idiom 画龙点睛, dotting the pupils on a painted dragon.
The story behind the character
眼
眼 is 目 (eye) with 艮 supplying the sound. Xu Shen's definition looks like a circle, 眼，目也, but the two characters started apart. 目 was the whole organ, lid and socket and all, and 眼 was the ball itself. 眼睛 stacks a second eye character on top for the same reason English says eyeball.
睛
睛 is 目 (eye) with 青 underneath for the sound. It means the eyeball, the dark center of the thing. Chinese pairs it with 眼 to make 眼睛, two eye characters in a row, which is a lot of eye for one word. 目不转睛: your eyes don't turn away from it.