The assault took place between 10.15pm and 11.30pm on Saturday, November 20, when a woman was attacked in London Road near the junction of Chichester Road.
The woman fell to the ground and was punched in the face, suffering a ruptured left eye, a fractured eye socket, a fractured cheekbone, and a deep laceration to the back of her head.
She was taken to Queen Alexandra Hospital to have urgent eye surgery.
A 46-year-old man from Portsmouth has been arrested on suspicion of grievous bodily harm with intent and remains in custody.
Officers believe several members of the public witnessed the incident and rushed over to help the woman while she was on the ground, according to a spokesman from Hampshire Constabulary.
He said: ‘We are appealing for those witnesses to come forward and provide us with information that could help the investigation.
‘Were you in the area at the time? Did you see the incident? Do you have any CCTV images or dash-cam footage that may assist our enquiries?’
Anyone with information regarding the incident is asked to call the police on 101 and give the reference number 44210472091.