Pacquiao dropped a unanimous decision to 29-year-old Horn which split opinion and prompted demands from some quarters for an investigation.
The WBO issued a statement confirming it had asked five judges to conduct a retrospective analysis of the fight via television and without sound.
The statement read: “The Jeff Horn vs. Manny Pacquiao bout results were controversial causing disputes amongst fans. For this reason, transparency is so important.
“The WBO does not have power to reverse the Judges decision based on discretion as it can only be revoked when fraud or a violation of Law has occurred, which is not relevant in this case.
“Based on this, five anonymous, competent Judges from different countries were asked to watch the bout without sound.
“From the results, it can be established that Pacquiao won 5 rounds while Horn won 7 rounds.”
The re-scoring tallied directly with two of the judges on the night, who both scored 115-113 for Horn, while a third judge, Waleska Roldan, scored 117-111 for the Australian.
Pacquiao’s promoter Bob Arum has already indicated he would be willing to make a re-match with Horn for November or December this year.
However, the 38-year-old, who holds a seat in the Filipino senate, claims his promotional agreement with Arum is at an end, and that he could well retire.