A man who left his victim with long-term double vision after a ''vicious beating'' outside a Woden bar has been sentenced to three months of weekend detention.

Mathew Neish, 25, was left with blood on his knuckles after an unprovoked but out-of-character bashing outside the Soul Bar in October 2010.

The attack was prompted by ''stupidly inappropriate remarks'' made by Neish to the victim's partner. Neish confronted the victim, fearing his partner might tell his girlfriend what he had said.

The victim said that Neish told him ''you need to sort your bitch out'' and, when the victim asked why, Neish said ''it doesn't matter, she's just a f---ing woman''.

Neish then punched the man repeatedly in the head, causing him to fall to the ground.

The victim's girlfriend said she thought her partner was dead as he fell and that the recurrent memory of the attack still ''fills her with horror''.

The assault continued while the victim was on the ground, with Neish bending over and continuing to punch him.

The victim was left with extensive injuries. His right eye was severely damaged and he suffers permanently from blurred vision and migraines, despite numerous operations.

He has repeated nightmares about the attack and has panic attacks, fears going out in public and suffers from depression.

Neish, the court heard, was a person of good character, acting as the backbone of his family business and raising $200,000 for multiple sclerosis charities. He had no criminal record and the attack was described as atypical.

On Friday, Justice Richard Refshauge sentenced him to two years' prison to be served through weekend detention.

But Justice Refshauge suspended the sentence from August 24, meaning Neish will only spend 28 nights in periodic detention over three months.

Neish will be subject to a good behaviour order for the next two years and will need to serve 150 hours of community service.