Crossword Genius

One with retina trouble has a tendency to remain unmoved (7)

Ross

I believe the answer is:

inertia

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'a tendency to remain unmoved' is the definition.
I can't tell whether this definition defines the answer.

'one with retina trouble' is the wordplay.
'one' becomes 'i' (Roman numeral).
'with' says to put letters next to each other.
'trouble' indicates an anagram.
'retina' is an anagram of 'nertia'.
'i'+'nertia'='INERTIA'

'has' is the link.

Can you help me to learn more?

(Other definitions for inertia that I've seen before include "I earn it (anag.)" , "Change-resisting tendency" , "Way of selling" , "Disinclination to respond" , "lack of action" .)

I've seen this clue in The Daily Express.
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