Type of lens through which a doctor perhaps looks (7)

I believe the answer is:

measure

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This might be a double definition.

'type of lens through which a doctor' is the first definition.
'measure' can be an answer for 'type' (thesaurus). I'm not sure about the rest of the definition.

'perhaps looks' is the second definition.
(I know that look is a unit of amount)

Can you help me to learn more?

(Other definitions for measure that I've seen before include "Take dimensions of" , "Establish the size" , "Tape" , "Extent" , "Unit of verse" .)

I've seen this clue in The Telegraph.

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