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Tamara Berezina, Eileen Buroff, Albert Khouri, Amir Cohen, Robert Fechtner; Unusual Cause of High Fixation Loss Rate during Standard Automated Perimetry Testing. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3936.
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Fixation loss rate is one of the visual field test reliability indices. High fixation loss rate is usually attributed to poor patient performance in maintaining regard of the fixation target. The aim of this work is to present an unusual mechanism of high fixation losses during visual field examination and a simple resolution.
We identified three otherwise alert patients noted to be accumulating a high fixation loss rate during monitored testing using Humphrey Field Analyzer (Carl Zeiss Meditec) Program 24-2. Every usual effort (including repeated patient instruction and repositioning) was made in order to reduce excessive fixation loss, but without success. Rhythmic head movements were noticed and the operator confirmed the presence of chewing gum in the mouth of each of these patients. Testing was repeated several minutes after chewing gum was removed with immediate resolution of the high fixation loss rate. We attempted to replicate these visual field testing conditions in three healthy volunteers instructed to chew gum during testing.
Visual field tests of three glaucoma patients prior to the moment when chewing gum in the mouth was identified were considered unreliable due to fixation loss that was as high as 82.7±9.3%. Visual field retest performed after the chewing gum was removed became reliable: fixation loss decreased to 6.3±5.7% (p=0.011 vs. the test with chewing gum in the mouth). Three healthy volunteers did not demonstrate difference in fixation loss rate with and without having chewing gum in the mouth (0.67±0.33% vs. 0.33±0.58%, p=0.42).
For some individuals, the pattern or magnitude of spontaneous movements resulting from chewing gum during visual field examination causes significant increase in reported fixation loss rate. This phenonomen appears sensitive to the individual’s technique of gum chewing. Clinicians should be aware of this possible cause of high fixation loss and the simple remedy; remove chewing gum prior to visual field testing.
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