A prisoner launched a savage attack on a fellow inmate with a make-shift weapon at HMP Edinburgh shortly after a religious service.
James Faulds, 29, attacked the 89-year-old at the prison on 28 April, 2018 after being told the man was a sex offender.
A court heard the victim survived what could have proven a life-threatening attack.
The victim was left with permanent scarring after the attack at the Saughton prison, Edinburgh Live reports.
Faulds has now been sentenced to a further seven-and-a-half years after admitting assaulting a fellow prisoner to his severe injury, permanent disfigurement and to the danger of his life.
He was given an order for lifelong restriction in 2011 after torturing a man in an Ayr flat over a £60 debt.
Faulds attacked the elderly prisoner at the conclusion of a multi-faith religious service in the chapel, after being told the man was a sex offender.
Lord Pentland issued the new sentence on Monday.
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He said: "James Faulds, you have plead guilty to committing a vicious attack on a fellow prisoner.
"You had armed yourself with an improvised weapon and deliberately slashed the victim across his neck with it at the conclusion of a religious service in Edinburgh prison.
"The injury you inflicted had the potential to endanger the life of your victim, although fortunately he is expected to make a full recovery. It is likely that he will be left with some permanent scarring.
"You have a concerning record of previous offending, dating back to 2007. I note that you have previously been convicted of offences of violence involving use of a knife.
"You are currently subject to an order for lifelong restriction imposed in this court in 2011 for an offence of assault to severe injury using a knife.
"Earlier this year you were convicted of possessing a bladed instrument in HMP Grampian on 29 March 2018."
