MOSCOW: Bolshoi artistic director Sergei Filin, who suffered serious eye damage and facial disfigurement in a horrific acid attack, should recover enough vision to return to his professional life, a German doctor treating him said Friday.

"We can say that we hope that Mr Filin will recover to a useable vision that will allow him to go back to his normal life and his professional life," Martin Hermel, an eye surgeon who is treating Filin at a German clinic, said at a news conference.

"As soon as my doctors say that I can see, I am going to return to work, and that is how it is going to be," said Filin, repeatedly wiping his eyes as he sat with the doctors at the German news conference, aired live on Russian television.

Filin, who wore dark glasses and a black woolly hat and scarf, smiled repeatedly and demonstrated how his doctors ask him to count their fingers to test his vision, as he spoke of his relief at the progress he was making.

"For me, of course, it's huge happiness," he said.

"I am feeling fine and am still full of strength."

Filin, 42, had sulphuric acid flung in his face outside his Moscow home in mid-January in an attack that left the world-famous Bolshoi troupe in crisis.

Police last week detained and charged three suspects including a top dancer at the theatre, Pavel Dmitrichenko, who was accused of masterminding the attack.

Filin underwent a number of operations on his eyes in Moscow before leaving for Germany, where reconstructive surgery is more advanced.

Doctors said the third-degree acid burns to his skin had healed but would cause severe scarring.

"The acid destroyed all layers of the skin of the face," said Professor Norbert Pallua, an expert in reconstructive surgery.

"This treatment has led to a healing of the wounds. Due to the initial depth of the injury, we have to anticipate severe scarring."

"This will necessitate a continued treatment of the scars, the skin, either with conservative or maybe with operative methods," Pallua said, speaking in English.

"The doctor always checks my face and always says that things are better and are going to be just great," said Filin, with the skin on his cheeks looking much less red and tight than when he left Russia last month.

"This lets me fall asleep at night," he said.

More than 300 members of the Bolshoi staff this week signed an open letter to President Vladimir Putin in defence of Dmitrichenko, saying they did not believe he would have been capable of ordering such a crime.

Filin said Friday he had not seen the open letter, but reiterated that he had suspected Dmitrichenko of involvement before his detention.

"The person who is being held now -- this person really was in the circle of people I suspected," he said.

The theatre's general director, Anatoly Iksanov, has repeatedly stated in interviews that he believes someone manipulated Dmitrichenko to organise the attack.

Dmitrichenko has said in court that he had asked for Filin to be beaten up, but not to be splashed with acid.

A senior police official told the Izvestia daily on Friday that investigators believe it was the suspected perpetrator, Yury Zarutsky, who chose to use the acid.

Filin was a star dancer at the Bolshoi before retiring and taking on the job of artistic director in 2011. He has linked the acid attack to a campaign of intimidation that included slashed tyres, hacked e-mails and threatening phone calls.