Police said two men pushed their way into a house in The Chase, Cottam, at around 5.25pm yesterday.
They demanded money before a struggle ensued, in which the 77-year-old male victim was knocked to the floor, suffering facial injuries.
He was restrained before being punched to the head.
The man’s 75-year-old wife attempted to defend herself but suffered a broken wrist and finger and severed tendons to her hand, for which she is receiving treatment at Royal Preston Hospital.
Information on items taken during the robbery has not been released.
Police are now appealing to anybody who may have been in the vicinity at the time, or who may have information that could lead to the offenders being found, to come forward.
DI Peter Danby, of Preston Police, said: “This was a nasty and cowardly attack on a couple in their 70s who found themselves targeted in their own home.
“We would urge anybody with information to contact us to help us identify the people that did this.
“We will leave no stone unturned so we would also encourage the offenders to hand themselves in before they are found.”
He added that an offence of this type is a rarity and the crime is not, at the moment, linked to any other incidents.
The offenders are described as male, wearing dark clothing and wearing woolly hats. One is thought to have had a beard and another a shaven head.
Anybody with information should contact police on 101 quoting log 1059 of January 26, 2016, or Crimestoppers, anonymously, on 0800 555 111.