What happens to Listing's plane during convergence?
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When looking about on a near surface (e.g. at the pattern on a bowl close
to the face) eye position
1) remains constrained to Listing's plane
2) but Listing's plane (LP) in each eye turns
temporally as does the eye's Primary Position
(PP).
As the vergence increases the temporal rotation of Listing's plane increases.
This means that the eyes become intorted (int) when looking up and extorted (ext) when looking down.
