Alternate cover test with prisms
All subjects underwent a second set of measurements, after a washing out
period of 2 minutes, during which a trained orthoptist estimated the
artificially induced skew using a system of refractory prisms opposed to
the subjects left eye and the ACT (Figure 1B) in a bright room. The
order of tests (orthoptist versus VOG) was randomly deranged to avoid a
potential order bias.