I believe you're referring to this sculpture?

The eyes of many sculptures were originally inlaid with precious stones, [like this one.] (http://www.britishmuseum.org/research/collection_online/collection_object_details/collection_image_gallery.aspx?partid=1&assetid=477968001&objectid=466397) The value of the stones made them a target for thieves and tomb robbers, who pried them from the sculptures apparently without concern for the artwork itself. It would also make sense (since the sculpture was found in a trash heap) that they were removed before discarding it, or melting the metal down to re-use.

Here's an excerpt from my Art History textbook:

"The founder of the Akkadian dynasty, Sargon I, reigned for over half a century, from c. 2332 to 2279 B.C., gaining control of most of Mesopotamia and the lands beyond the Tigris and Euphrates Rivers. A near-lifesized bronze head may be his portrait. Its high level of artistry and technical skill indicates that metal sculpture on a monumental scale was not new, but earlier examples have not survived. It was made by the cire-perdue, or lost-wax, method. Throughout history metal objects were often melted down for re-use, making large-scale metal sculptures from antiquity rare today. This head, found on a trash heap, is all that remains of a full-length statue.

The power of this work resides in the self-confident facial features emerging from the framework of stylized hair. The eye sockets would originally have been inlaid with precious stones, which have since been gouged out - perhaps for their intrinsic value, or perhaps to destroy the power of the image."

Schneider Adams, L., Art Across Time