The Ireland half-back was injured when one of the straps on a speed training sled recoiled and struck him in the left eye. The accident caused a bleed within the eye which initially affected his vision although the bleeding has now been stabilised.
The injury rules O'Leary out of Ireland's last 2011 RBS 6 Nations game against England in Dublin on Saturday.
Ireland's only other injury concern for the game is also at scrum-half, where Leinster's Eoin Reddan is continuing to be monitored by medical staff following his concussion in the first minute of the 19 v 13 defeat to Wales in Cardiff last weekend.
England travel to Dublin this weekend with the Grand Slam still on the cards whilst Ireland will look to bounce back from defeat in Wales and end their campaign on a high ahead of the World Cup.
"England are the last game in the championship and our last competitive game before the World Cup," said Ulster hooker Rory Best.
"England are on a great roll at the moment so it's a real opportunity to get back to winning ways and secure our first Six Nations win at the Aviva Stadium.
"It's a game that we desperately want to win."
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