Luxottica has appointed to its board a close associate of the group's founder Leonardo Del Vecchio in a move that could deepen governance concerns at the world's largest eyewear maker after the departure of three CEOs in quick succession.

The maker of Ray Ban and Oakley sunglasses said on Tuesday Francesco Milleri, a business and IT consultant, had been appointed "director with deputy functions to assist the Executive Chairman (Del Vecchio)".

Sources close to the matter have told Reuters that Milleri, a long-standing aide to the Del Vecchio family, has been playing an increasingly active role at Luxottica in the past two years, and that upset some top executives.

His board appointment cements his position as the right-hand man to 80-year old Del Vecchio but is unlikely to quell fears about management instability and the ability of the group's founder to steer the glasses company in a more challenging market.

"As practice goes this is hardly the best, especially after Del Vecchio concentrated powers in his own hands. It also worsens the profile of the board," a corporate governance expert said speaking on condition of anonymity.

Del Vecchio tightened his grip on the company he founded in 1961 by taking on executive powers at the end of January, when Luxottica announced the exit of co-CEO Adil Mehboob-Khan. Massimo Vian, who had been joint CEO in charge of products and operations, became the sole chief executive.

On Tuesday, Del Vecchio said in a statement that Luxottica had a very clear governance structure and that Milleri's appointment did not change that.

"Milleri is not a new CEO but will act under my coordination and under my responsibility as executive chairman," he said.

Del Vecchio is well regarded and credited with turning Luxottica into a global player by buying coveted brands. He owns 66.5 percent of Luxottica, the world's top spectacles maker, with revenues of 9 billion euros ($9.76 billion).

But the recurrent management changes are raising questions about his succession plans and strategy, analysts said.

Khan, who had joined as co-CEO from Procter & Gamble only a year ago to smooth over a previous management crisis, was the third CEO to leave the company in 17 months.

Long-standing CEO Andrea Guerra stepped down in 2014 following a rift with Del Vecchio. His successor, Enrico Cavatorta left after only six weeks into the job, also due to differences with Del Vecchio.

The upheaval has come at a delicate juncture for Luxottica which is looking to increase its presence in Asia and develop more retail and online business. Year-to-date, its shares have fallen around 12 percent.

On Tuesday Luxottica confirmed its outlook for mid-to-high single digit sales growth to 2018 but trimmed profit guidance to help fund investments. Profits to 2018 are expected to grow at 1.5 times sales growth, down from a long-standing "rule of thumb" guidance of two times.

The company, which reported a 22.5 percent rise in adjusted operating profit to 1.4 billion euros last year, said it planned to spend more than 1.5 billion to 2018. Spending will focus on boosting online and distribution channels and beefing up retail business in North America and Asia with more than 1,000 new outlets to be opened.

"We want smaller, leaner shops so we can open more of them...and allow orders to be made using mobile technology," CEO Vian told Reuters.

Vian dismissed recent press speculation that the group was considering an acquisition of Essilor or Carl Zeiss.

"There are no M&A talks under way with these companies."