Estimation of the short-term fluctuation from a single determination of the visual field

The short-term fluctuation in regular grid threshold static fields is commonly determined from repeated observations of a number of threshold points. In this study we estimated the short-term fluctuation from a single determination of the field. Sixty-two eyes of 62 patients were tested, using three consecutive repetitions of a Humphrey 24-2 full threshold program. The resulting grid patterns were examined using a modified version of the statistical technique of trend-surface analysis. Polynomial surfaces of increasing degree were fitted to the data over the grid. The residual variances after detrending the surface correlated very well with the direct estimates based on the triple observations at each point (correlation coefficients of log-transforms of 0.8 and better). We conclude that short-term fluctuation (the square root of the variance) can be estimated with good reliability from grids of single threshold determinations.