The 19-year-old victim was at a venue in Bourke Street on February 17 last year when Cameron Scerri, 23, entered the rear of the property by scaling the fence.

Scerri, who had consumed "significant amounts" of alcohol, offered the teenager drugs, but he declined.

While walking in front of the teen, Scerri swung his right arm backwards and hit his victim in the face, causing a ruptured optical nerve behind his right eye.

The teen was unable to see from his eye, and the injury was inoperable.

Scerri had a seizure while being arrested and was deemed unfit for interview, having not taken his prescription medication.

He later pleaded guilty to recklessly causing serious injury.

County Court of Victoria Judge Paul Lacava, while sentencing on Thursday, described the injury as serious or even catastrophic.

"The victim has permanently lost total vision in his right eye," he said.

"He (the victim) asked appropriately: 'Why me? And what did I do to have you hit me and render me blind in one eye?'"

Judge Lacava described Scerri's offending as cowardly and unprovoked, but also noted the young man's "tragic background".

He said Scerri had experienced violence from a young age, including having his arm fractured during an altercation between his parents when he was six months old.

"You appear to have no one in your life who you can look up to for guidance and leadership," Judge Lacava said.

"I can only opine that your prospects for rehabilitation appear bleak."

Scerri, who has already served 382 days in pre-sentence detention, must serve a minimum three years before he is eligible for parole.

Australian Associated Press