How much better it is than myopia? (3,5)

'than myopia?' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'how much better it' is the wordplay.
I cannot really see how this works, but
'much' could be 'far' (I've seen this in other clues) and 'far' is found in the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
The remaining letters 'sigh' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'is' acts as a link.

Can you help me to learn more?