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S. Joshi, D. Richards, P. Kamath; Logarithmic Versus Non-logarithmic Behavior of the Quadrant Sum in Humphrey V-Spot Visual Fields. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1069. doi: https://doi.org/.
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The Zeiss-Humphrey V-spot automated threshold visual field test ("V-spot") is frequently used clinically for patients with advanced field loss and/or decreased visual acuity. We compared the behavior of the V-spot quadrant sum (QS) in the logarithmic (db, geometric) versus non-logarithmic (arithmetic) domains.
A total of twenty-seven Fastpac and Full Threshold 24-2 V-spot tests of seven eyes of five patients were transferred to a Sun Workstation. Range of QS was 0 to 419 db. The individual db sensitivities for the 108 quadrants were analyzed, using Interactive Data Language software, to produce the arithmetic mean (AM) and geometric mean (GM) for each quadrant. Mathematically, log(GM) = QS / 10 / (number of points in the quadrant). Standard deviations of the original db values and of their arithmetic equivalents were also computed for each quadrant. Arithmetic values were converted to db for comparison purposes.
For 4 ranges of QS (0-100, 101-200, 201-300, and >300), average AM (GM) were, in db: 7.8(3.3), 18.9(11.5), 24.1(18.9), 28.4(26.5). Average standard deviations for the same intervals were: 5.5(4.6), 6.9(9.0), 4.7(5.2), 2.8(5.2).
The QS (or its equivalent, GM) consistently underestimates the average sensitivity of the quadrant for all ranges of QS. Standard deviations computed in the logarithmic domain are sometimes significantly greater than in the arithmetic domain. QS may not be the ideal estimator of average loss per quadrant in V-spot tests.
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