Hi
As you are seeing single thread floater , a proper eye examination is needed . One needs to rule out any inflammation in the eye
Do you wear glasses , if yes myopia causes degeneration of vitreous ( a jelly infront of retina) . It may be result if that
But many a times it is due to physiological entopic phenomenon. In that cases you need not worry about it
So get a proper eye examination done first
Next Steps
Please visit an ophthalmologist or consult in detail to formulate a diagnosis