MILAN (Reuters) - Italy's Luxottica and France's Essilor have agreed a 45-billion euro merger deal to create a global powerhouse in the eyewear industry, a source with knowledge of the matter said.

The deal, one of Europe's largest cross-border tie-ups, is expected to be announced before the market opens on Monday. It will see Luxottica's 81-year old founder Leonardo Del Vecchio take a 31 percent stake in the merged group through his family holding Delfin, the source said.

(Reporting by Gianluca Semeraro and Paola Arosio, writing by Silvia Aloisi)