The TV campaign and an accompanying marketing brochure featured the two-time Open winner discussing the benefits of laser eye surgery.
Harrington said in the ad: "People often ask me: how can I improve my game? I tell them the secret is to stay focused. And of course it's important to have great vision. I need to be able to look down the line, focusing clearly on the target. My advice? Visit Optical Express. It could help your game too."
Rival laser eye surgery firm Ultralase said that the claims in the ad were misleading and questioned whether they could be substantiated. The company also challenged the testimonial attributed to Harrington in the brochure as it implied that he had undergone laser eye surgery at Optical Express, despite the fact that Ultralase "understood that was not the case".
The Advertising Standards Authority had previously upheld 23 of the 25 complaints against the ads raised by Ultralase, and has now decided to ban the campaign entirely.
Optical Express had called for an official review of all the complaints, and claimed that Harrington's testimonial had "extolled the benefits of laser eye surgery for a professional golfer and advised that customers who might want the same benefits from laser eye surgery should visit Optical Express".
The company said that its TV ad did not claim that Harrington had undergone laser eye surgery at Optical Express, and added that there was "no ambiguity, misleading content or impression, implication or innuendo in the ad".
However, the ASA said that the testimonial and the TV ad were both misleading because they suggested that Harrington, who has had laser eye surgery but not with Optical Express, had enjoyed the benefits of the procedure with the company he was endorsing. The ASA opted to maintain its earlier decision to uphold 23 of the 25 complaints made by Ultralase, and banned the TV ad.
"We noted that the TV ad did not contain a specific statement that Padraig Harrington had had laser eye surgery, or that he had had laser eye surgery at Optical Express," said the watchdog.
"However, we considered that the claims "And of course it's important to have great vision ... My advice? Visit Optical Express, Europe's number one provider of laser eye surgery" and "It could help your game too" was likely to be interpreted by viewers as a claim that Mr Harrington had experience of the benefits of laser eye surgery at Optical Express.
"Because we considered that the ad implied that Mr Harrington had had laser eye surgery at Optical Express, and because we understood that was not the case, we concluded that the ad was misleading."
Last October, the ASA banned a Waitrose TV ad campaign featuring Heston Blumenthal for making misleading claims about pork. The watchdog also censured an advert for an action movie starring Jason Statham in June due to its "graphic violence".