PARIS/ZURICH (Reuters) - France's competition authority is investigating drugmakers Roche (>> Roche Holding Ltd.) and Novartis (>> Novartis AG) on suspicion they were involved in anti-competitive practices in relation to eye disease treatments, the companies said on Thursday.

This is the second time in as many months that the Swiss drugmakers have faced regulatory scrutiny over treatments for wet age-related macular degeneration (AMD)- a leading cause of blindness among the elderly.

A statement on the French authority's website said it had conducted "search and confiscation" operations on April 8 in relation to treatments for wet AMD, but it did not name the companies involved.

Spokeswomen for both Roche and Novartis confirmed the French authorities had started an investigation regarding treatments for the eye condition and said they would cooperate fully.

Roche denied that the two companies had colluded: "Roche confirms there is no agreement between Roche and Novartis that restricts competition.

Last month, Italy's antitrust authority said Roche and Novartis had colluded to try to stop cancer drug Avastin from being used to treat AMD and fined the companies 182.5 million euros (151.4 million pounds).

The regulator accused the two Basel-based firms of striking an alliance to prevent distribution of Roche's Avastin in favour of the more expensive drug Lucentis marketed by both Roche and Novartis.

While Lucentis is specifically approved to treat wet AMD, it costs far more than Roche's cancer drug Avastin which works in a similar way when split into smaller doses and is widely prescribed on a so-called "off-label" basis.

The companies have cautioned against substituting Avastin for Lucentis and say doing so puts cost savings ahead of patient needs. But critics say Novartis and Roche have split the market to maximise profits.

Lucentis is marketed by Novartis outside the United States and is the company's third-biggest seller with sales of $2.38 billion last year.

Sales of Lucentis for Roche, which markets the treatment in the United States, were 1.69 billion Swiss francs ($1.9 billion) in 2013.

(Reporting by Andrew Callus, Chine Labbe and Caroline Copley; Editing by Pravin Char)

Stocks treated in this article : Roche Holding Ltd., Novartis AG