The 19-year-old was using a pickaxe to lever up wooden floorboards at Hyde Mill, on Ashton Road in Hyde on 8 September 2009, when he was hit in his left eye by a splinter.
Dovestone Contractors Ltd, which has an annual turnover of £2.7m, was prosecuted by the Health & Safety Executive (HSE) after it failed to ensure the teenager wore goggles or other eye protection.
Trafford Magistrates' Court heard that the teenager, from Bradford in West Yorkshire, had been working for the company for one and a half years before the incident. He had been helping to remove wooden planks from four floors at the mill, ahead of its demolition.
Neil Martin, the investigating inspector at HSE, said: "A young man has suffered a life-long, irreversible injury because he wasn't given safety goggles that would have cost less than £5.
"He hasn't returned to work in the demolition industry because he's frightened of losing the sight in his other eye. He may also have difficulty trying to get a drivers licence. This was a life-changing injury.
"Dovestone Contractors should have known there was a serious risk of its workers being blinded by splinters if they didn't wear eye protection while using pickaxes to lift floorboards. This is required by law and there is simply no excuse for such a basic health and safety error."
Dovestone Contractors Ltd pleaded guilty to breaching Regulation 4(1) of the Personal Protective Equipment at Work Regulations 1992 by failing to provide eye protection for its employees.
The company, of Ocean Village in Southampton, was ordered to pay £4,000 towards the cost of the prosecution in addition to the fine on 1 December.