A laser show at a music festival injured more than 30 people, Russian news reports say. Some concertgoers lost up to 80 per cent of their vision after attending the Aquamarine Music Festival on July 5, the newspaper Kommersant reported. Twenty people are undergoing treatment in Moscow hospitals, said Elena Grishina, the head doctor at the Moscow Ophthalmological Hospital, the RIA-Novosti news agency reported on Monday. "It is just a deterioration in the sharpness of the eyesight, not a burn," she was quoted as saying, and said she could not confirm the injuries came from lasers. "The treatment is not very pleasant. It involves a lot of needles," Grishina said. "But all the patients are in optimistic spirits, and we are hoping for a good result." According to the reports, concertgoers said the festival's dance floor was covered by a canopy because it was raining. The lasers were pointed horizontally under the tent instead of into the sky, which led to the injuries, the reports said. "After five or 10 minutes on the dance field, I couldn't see anything," a young man in sunglasses identified as a concertgoer said on NTV television. "I could see out of my left eye, but my right eye is all fog." The broadcast showed video from the festival recorded by mobile phones, one of which appeared to burn out when a laser shone on it. The festival was held in the Vladimir region east of Moscow. During the summer, techno music enthusiasts often organise open-air raves on empty fields outside Moscow. The injured concertgoers plan to take legal action against the festival's organisers, NTV reported. A representative of the Vladimir regional government said the festival was organised illegally without proper permits. Police in the town of Kirzhach, where the festival was held, refused to comment. Most of the injured concertgoers sought treatment at two Moscow hospitals, Kommersant reported. No one answered the telephone at either hospital on Monday. Grishina was quoted as saying there were no immediate plans to release the patients.