Swirling mist follows Greek character hiding onset of terrible eye condition (10)

'eye condition' is the definition.
'stigmatism' can be an answer for 'condition' (stigmatism is a kind of condition). I'm unsure of the 'eye' bit.

'swirling mist follows greek character hiding onset of terrible' is the wordplay.
'swirling' indicates anagramming the letters.
'follows' means one lot of letters go next to another.
'greek character' becomes 'sigma' (letter from the Greek alphabet).
'hiding' means one lot of letters goes inside another.
'onset of' indicates taking the first letters.
The initial letter of 'terrible' is 't'.
'sigma' placed around 't' is 'stigma'.
'mist' anagrammed gives 'tism'.
'tism' put after 'stigma' is 'STIGMATISM'.

Can you help me to learn more?