Points of a normal visual field are not statistically independent.

The aim of the present study was to determine whether the sensitivity values at individual test locations in a normal visual field are statistically independent. A total of 144 eyes of 144 normal subjects were tested with the Humphrey Field Analyzer, program 30-2. For each point in the visual field the pairwise correlation of sensitivity values to all other points was calculated together with the angular distance between points. The overall 2775 correlation coefficients were plotted as a function of angular distance. With increasing distance the correlation coefficients decrease continually from 0.63 (distance 6 degrees) to approx. 0.5 (distance 30 degrees and above). The strong relationship between adjacent points that is present at up to 30 degrees is destroyed by intraindividual randomisation of the visual field data. Interindividual randomisation abolishes any correlation. Adjacent locations in a normal visual field are strongly statistically related to each other. Two patterns may be separated; part of the correlation is an intrinsic neighbourhood effect present up to 30 degrees and part is due to the observation that the sensitivity values of a specific visual field are obtained from the same subject and are thus not independent. Therefore, for the calculation of normal values, procedures have to be developed that take the relationship between neighbouring points into consideration.

The different effects of aging on normal sensitivity in flicker and light-sense perimetry.

PURPOSE: To verify whether or not an accelerated loss at an older age for normal sensitivity in the central visual field is present when using the stimulus configuration of conventional white/white automated light-sense perimetry and the stimulus configuration of the automated flicker perimeter developed by one of the authors (BJL). METHODS: One hundred thirty eyes of 130 normal subjects aged 9 to 86 years were tested with the Humphrey-Field-Analyzer 640, program 30-2, and our automated flicker perimeter. In addition, short introductory learning programs were used for both techniques. All tests were performed in random order. RESULTS: Mean critical flicker fusion frequency shows a linear loss over the entire age range (r = -0.5546, P < 0.0001, slope a = -0.3820 dB/decade), whereas mean light difference sensitivity decreases only slightly up to 46 years of age (r = -0.0118, P = 0.9226, slope a = -0.0153 dB/decade), with a marked acceleration above 46 years of age (r = -0.7304, P < 0.0001, slope a = -2.0640 dB/decade). CONCLUSIONS: The absence of an accelerated loss at an older age for critical flicker fusion frequency (CFF) and the presence of such a loss for light-difference sensitivity (LDS) might be attributed to the independence of a flickering stimulus from distributing effects induced by the ocular media at an older age as proposed by one of the authors. The different age effects for CFF and LDS could also be explained by different age-related losses at different sites and for different neuronal populations throughout the visual pathways.