The palpebral fissure is the elliptic space between the medial and lateral canthi of the two open lids. In adults, this measures about 10mm vertically and 30 mm horizontally.
This definition incorporates text from the wikipedia website - Wikipedia: The free encyclopedia. (2004, July 22). FL: Wikimedia Foundation, Inc. Retrieved August 10, 2004, from http://www.wikipedia.org