Normal visual fields measured with Octopus Program G1 - I. Differential light sensitivity at individual test locations

Exact knowledge of the normal variation of visual fields and the influence of age upon them is essential to differentiate normal from abnormal results, e.g., in glaucoma suspects. This study evaluates the normal variability of differential light sensitivity at individual test locations and incorporates a data base of a multicenter study performed with Octopus 201 perimeters using Program G1. The 824 fields thus obtained included 139 fields of 139 healthy volunteers who had undergone two previous visual fields and completed all three phases of the program. Sensitivity decreased linearly with age, an effect which for individual test locations ranged between 0.036 and 0.107 dB/year and which became more pronounced towards the periphery. On average, the age-related effects explained only 17% of the interindividual variation (range 4%-31%). The interindividual variation within a test averaged 4.6 dB² and revealed a moderate, but quadratic increase towards the periphery. The intra-individual short-term variation was considerably lower, averaging 2.2 dB². There was a similar modest, quadratic increase of the intra-individual variation towards the periphery. The results may help distinguish incipient disease manifestations from normal variation of perimetric results. Furthermore, the results give insight into the calculation of global visual field indices.