In the present work, we use random-dot stereograms to test a possible relat
ionship between associated phoria and stereopsis. We determined, using a mo
dified constant-stimulus method, the disparity range that indicates the max
imum range at which stereoscopic correspondence can be achieved. A total of
27 observers took part in the experiment. The value of the disparity range
as a function of the associated phoria (measured with a Mallet unit) seems
to indicate that greater associated phoria (fixation disparity) correlates
with a deterioration in stereoscopic vision, reducing the disparity range
and therefore the space region in which stereoscopic vision can be attained
.