dark vergence & phoria

[P3D Peter Abrahams <telscope@xxxxxxxxxx>]

The question was raised as to a correlation between dark vergence &
esophoria or exophoria.  _Binocular Vision and Stereopsis_, Ian Howard &
Brian Rogers (1995, 730pp, $120) has a 60 page chapter on vergence, and
p388 states: "phoria...should be highly correlated with dark vergence.  The
two measures are correlated, but horizontal phoria is typically more
divergent than dark vergence...could be due to the fact that the
accomodative state of an eye is different in dark vergence and in
phoria....In dark vergence the eyes are probably accomodated at a near
distance whereas phoria is measured with the subject accomodated on a
distant object...for most subjects, phoria and dark vergence were highly
correlated...viewing through 0.5 mm pupils."  (The pinholes are to remove
the effects of accomodation,  everything is in focus through a pinhole.)

This does not directly answer the question of the relation between
esophoria -- exophoria and dark vergence, but it is such an interesting
subject that I was sure any additional input would give someone a thrill.

A few months ago, a question on tech3d concerning accomodation &
convergence motivated me to write up a very wordy review of that topic as
covered in this book.  That is in the tech3d archives, or I could e-mail it
to interested parties. 
_______________________________________
Peter Abrahams   telscope@xxxxxxxxxx
the history of the telescope, the microscope,
    and the prism binocular


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