Body chemical, with iodine and phosphorus, found in part of eye (5)

I believe the answer is:
lipid
'body chemical' is the definition.
The definition and answer can be both substances as well as being singular nouns.
Maybe there's a link between them I don't understand?
'iodine and phosphorus found in part of eye' is the wordplay.
'iodine' becomes 'I' (I is the chemical symbol for iodine).
'and' is a charade indicator (letters next to each other).
'phosphorus' becomes 'P' (P is the chemical symbol for phosphorus).
'found in' means one lot of letters goes inside another.
'part of eye' becomes 'lid' ('lid' is part of 'eye').
'i' put after 'p' is 'pi'.
'pi' going within 'lid' is 'LIPID'.
'with' acts as a link.
Can you help me to learn more?
(Other definitions for lipid that I've seen before include "fat, perhaps" , "One of the essential structural components of living cells" , "fatty stuff" , "oily substance" , "Organic compound" .)
