A group of Russian partygoers have lost partial vision after laser lights burned their retinas at an outdoor rave near Moscow, Reuters reported.

According to Reuters, Moscow health officials confirmed 12 cases of laser-blindness and 17 others were treated for injuries. Attendees of the July 5 festival in Kirzhach reportedly began seeking medical attention a few days after the show, complaining of eye and vision problems, Reuters said.

Heavy rains reportedly forced organizers to erect tents to shield attendees. As a result, lasers that would normally shine upwards instead partially illuminated into the ravers’ eyes, Reuters reported.

“They all have retinal burns, scarring is visible on them,” one ophthalmologist told Russian newspaper Kommersant. “Loss of vision in individual cases is as high as 80 percent, and regaining it is already impossible.”

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