A grandfather has spoken of his fury after his teenage granddaughter had ammonia thrown in her face in an apparently unprovoked attack.
The 13-year-old was walking in Islington, north London, with two friends at 2210 BST on Saturday when they were attacked.
The girl has been left partially blind in one eye. Doctors have said it could be permanent.
A boy, 14, has been arrested and bailed to return to police in late June.
The girl has asked not to be identified because she is afraid of another attack.
Her grandfather told the BBC: "A crowd of boys came riding past her and one of them sprayed her with ammonia.
"She was rushed to Moorfields Eye Hospital.
"Now she has to have eye drops all the time and go back to the hospital every day to have her eyes cleaned."
He continued: "Now the kids are not carrying knives, they are carrying chemicals instead.
"It's so horrible that someone could do what they did - it was a completely unprovoked attack.
"I just want people to be aware of what's going on. Next time it could be a mother with a newborn baby."
The girl has been left with blurred vision in one eye.
A Metropolitan Police spokeswoman said: "Police were called to reports that three teenage girls had a noxious substance thrown at their faces.
"Police arrived approximately five minutes later and gave first aid to a 13-year-old, and two 14 year-old girls.
"The girls told the police that they had been approached by a large group of boys, one of whom threw a liquid chemical at them."
Detectives urged anyone with information about the attack to come forward.