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D.G. Birch, K.G. Locke, M. Klein, J. Felius; Measures of Static Perimetric Field Progression in Retinitis Pigmentosa . Invest. Ophthalmol. Vis. Sci. 2005;46(13):519.
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Purpose: Static perimetric fields are widely used to follow the progression of retinitis pigmentosa, but there is no widely–accepted field–based outcome measure for use in clinical trials. Here we evaluate the sensitivity of potential measures of disease progression for use in future treatment trials. Methods: We identified 30 patients with retinitis pigmentosa (ages 9 to 53 yrs) who had a) Humphrey static perimetric fields covering an interval of two to four years and b) > 20% decline in cone ERG amplitude over the interval. Program 30–2 was obtained from one eye of all patients; program 60–4 was obtained from those retaining function beyond 30 degrees eccentricity. For each patient, a transitional ring was defined within the zone between relatively healthy field and non–seeing field. The ring consisted of locations with dB values in the teens adjacent to locations with values typically <10. This ring was defined on the initial visit and sensitivity within the ring was compared on subsequent visits. All dB values were converted to linear units for subsequent analyses. Sensitivity in the transitional ring was compared to total field sensitivity and sensitivity in the macula (central 4 points). Results: 21 patients showed consistent loss of sensitivity in field parameters, while 9 showed either no change or improvement. Percent change in total sensitivity was significantly correlated with both the percent change in the transitional ring (r=0.79) and the percent change in the macula (r=0.76). The slope of each regression function was close to unity (0.89 and 1.03, respectively) . Conclusions: We compared two derived measures of field sensitivity to the global measure of total field sensitivity. Across this group of patients, neither derived measure showed an advantage over total sensitivity in sensitivity to progression in retinitis pigmentosa. These findings are consistent with a "sinking island" model of progression in retinitis pigmentosa and counter to the traditional "field constriction" model inferred from Goldmann kinetic perimetry.
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