Katherine Jenkins sleeps with her eyes open.

The 33-year-old classical singer admits she suffers from the rare condition Nocturnal Lagophthalmos, which means she's unable to shut her eyes completely when she nods off.

She said: ''The best chat up line to ever come my way is, 'Was you father a thief because he must have stolen the stars from the skies and put them in your eyes?'

''Speaking of which I always sleep with my eyes open.

''My eyes don't close properly - they are always at least half open - and when I go to sleep I look like I'm still awake. And I don't really have dreams either. My mum would always say, 'Katherine, are you awake or are you asleep?' ''

The blonde beauty has battled with the medical condition, which it is thought to only affect 10 per cent of the population, since she was a youngster.

Medical professionals believe Nocturnal Lagophthalmos is a form of facial paralysis, which leads to dry and damaged eyes, but the cause of the condition is not yet known.