Pseudo-loss of fixation in automated perimetry.

During automated perimetry with the Humphrey Visual Field Analyzer, field examinations are labeled unreliable whenever the reported rate of fixation loss is 20% or more. The reported rate of fixation loss results in part from times when the patient's gaze drifts from the fixation point during the examination, but also in part from technical artifacts such as faulty initial localization of the blind spot or false-positive responses by the patient. It was found that technical artifacts caused nearly half of the instances in which a field examination had a reported fixation loss rate of greater than 20%. It was also found that the perimetrist can prevent the artifacts, with the result that the frequency of field examinations labeled as having excessive fixation loss fell from 26% to 14%.