Not emotionally affected by blurred vision (3-4)
I believe the answer is:
dry-eyed
'not emotionally affected' is the definition.
The answer and definition are not the same part of speech. However, adjectives and past participle verbs can sometimes define each other.
'blurred vision' is the wordplay.
I cannot quite see how this works, but
'vision' could be 'eye' (I've seen this in another clue) and 'eye' is located in the answer.
This explanation may well be incorrect...
'by' is the link.
Can you help me to learn more?
(Other definitions for dry-eyed that I've seen before include "Unmoved" , "Tearless" , "Not crying" , "Without a tear" .)