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S. Whitford, S. Newman; RAREbit: a novel perimetric strategy for detection of subtle optic nerve dysfunction. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):234.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Because of visual system redundancy, subtle visual field defects may not be obvious on standard automated perimetry (SAP). A recently developed program (by Dr. Lars Frisen) that uses tiny points of light, RAREbit, purportedly better detects subtle defects. We undertook a study of patients with known asymmetric optic nerve function, yet normal fields using a Humphrey 24–2 SITA–fast program (size III test object) to determine the ability of RAREbit perimetry to accurately detect subtle field defects missed by SAP. Methods: 5 patients (4 women, 1 man) with equal acuity but asymmetric optic nerve function (based on the presence of an afferent papillary defect) enrolled in the study. All 5 with normal (symmetric with the uninvolved eye) Humphrey 24–2 SITA–fast fields using a size III test object were retested using the 24–2 full–threshold program utilizing a size I test object followed by the RAREbit "rabbit" test utilizing the protocol outlined by Lars Frisen. The three results for each eye were then compared side by side for asymmetry that would corroborate the asymmetric optic nerve function. Results: The RAREbit perimetry "rabbit" test invariably (5 of 5) detected the eye with the afferent pupil defect. This was corroborated by the size I FT Humphrey 24–2 in each case. The "rabbit" test took 59% of the time required of the Humphrey 24–2 FT size I test (average "rabbit" time 6 minutes 45 seconds compared to average 24–2 FT size I time of 11 minutes 26 seconds.) Conclusions: RAREbit perimetry can detect subtle field defects that are not seen on Humphrey 24–2 SF size III testing. The test is faster and easy to perform.
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