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Michael Kalloniatis, Sieu Khuu; A Paradigm Shift in Visual Field Testing Using White-on-White Standard Automated Perimetry (SAP). Invest. Ophthalmol. Vis. Sci. 2014;55(13):3534. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
White-on-white (w/w) SAP is the gold standard in assessing visual function in ocular disease. SAP typically uses Goldmann size III presented at low photopic light levels (durations of 100-200ms). Although test duration is outside temporal summation (Bloch's law) for different retinal eccentricities, test size is not scaled for retinal eccentricity. Previous work (Sloan, VR 1961; Redmond et al IOVS 2010) showed a greater loss for smaller test stimuli (within Ricco's law). We determined if test sizes within Ricco's area (from normative population data of Khuu & Kalloniatis, ARVO 2014) to assess if w/w SAP using Goldmann III target is suitable for early disease detection.
We measured thresholds (30-2 or 10-2) using the Humphrey Visual Field analyser for the 5 target sizes (Goldmann I-V) for 5 normal subjects, 4 early glaucoma and 2 subject with early macular degeneration. The location of Ricco's critical area (Ac) was determined using a two line fit for various eccentricities and locations and compared Ac with normative data from Khuu & Kalloniatis (ARVO 2014). We also compared threshold values for the disease population at various eccentricities to establish the amount of loss when using test targets within or outside the Ac of Ricco's law.
The estimated Ac for the 5 normal subjects at the various eccentricities and location was similar to the population study. The standard Goldmann III target was within Ricco's law at more eccentric locations of the 30-2 paradigm falling either in the Piper's law region or linear region for eccentricities <40 degree diameter. When comparing affected visual field location in the glaucoma or macular degeneration patients to corresponding unaffected areas or normative data, we mostly find a larger threshold elevation when using test stimuli within the Ac region.
In ocular disease within the central 40-degree diameter, the use of test stimuli within the Ac region provides a larger and earlier detection of visual field loss. The use of Goldmann III test size for eccentricities within 40-degree diameter, assesses visual function at different parts of the spatial summation continuum: this has implications for the accuracy of global and local indices derived from SAP. We have also developed a transform and define a new dB* value which advantageously enables comparison of thresholds within Ricco's law irrespective of test size.
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