Watching very closely, as in The buyers at the fashion show were all eyes. Worded slightly differently (with all one's eyes), this idiom dates from the mid-1500s. Also see its counterpart, all ears.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.