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Quantitative Measurement of Fixation Stability During RareBit Perimetry and Humphrey Visual Field Testing

Lin, Shawn R. BS, MS*; Lai, Isabella N. BA*; Dutta, Sanjeev MD, MA; Singh, Kuldev MD, MPH*; Chang, Robert T. MD

doi: 10.1097/IJG.0b013e31829d9b41
Original Studies
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Purpose: To compare fixation stability and fixation loss between the Humphrey Field Analyzer (HVF, static fixation target) and the RareBit computer-based perimeter (RBP, kinetic fixation target) during visual field testing.

Methods: Fourteen healthy volunteer subjects wore an ASL Mobile Gaze Tracker as they completed HVF 10-2 and RareBit central field tests in a random order. Fixation stability, defined as the average distance from the fixation target to the subject’s gaze location, was calculated using data from the processed video capture. Fixation loss, defined as eye closure or a deviation of >20 degrees from the fixation target, was also measured. All subjects were surveyed regarding test preference.

Results: Use of the RBP kinetic target was associated with 18% improved fixation stability compared with the HVF static target (P=0.02). Nine of 14 study subjects demonstrated better fixation with RBP compared with HVF. Subjects demonstrated decreased fixation loss during RBP (0.9 s) compared with HVF (10.0 s) (P=0.002). Eighty-six percent of study subjects preferred RBP over HVF.

Conclusions: Use of the RBP kinetic fixation target is associated with consistent fixation stability and decreased fixation loss compared with the HVF static target. This improvement in fixation stability may result from decreased perception interference (Ganzfeld, Troxler, and binocular rivalry effects), and may help account for the greater comfort reported with RBP compared with HVF.

*Department of Ophthalmology, Byers Eye Institute at Stanford University

Department of Pediatric Surgery, Stanford University School of Medicine, Palo Alto, CA

Supported by American Glaucoma Society MAPs Grant.

Disclosure: The authors declare no conflict of interest.

Reprints: Robert T. Chang, MD, Department of Ophthalmology, Byers Eye Institute at Stanford University, Stanford University School of Medicine, 2452 Watson Court, MC 5303 Palo Alto, CA 94303 (e-mail: viroptic@gmail.com).

Received May 18, 2012

Accepted April 14, 2013

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