Diffuse and localised visual field defects to automated perimetry in primary open angle glaucoma

The occurrence of generalised or diffuse visual field depression in primary open angle glaucoma (POAG), in contrast to the presence of characteristic localised defects, is controversial. The frequency of diffuse visual field loss to automated static perimetry in the early stages of POAG was determined and compared with the frequency of localised defects. Twenty-five eyes of 25 consecutive POAG patients who met the selection criteria were tested on the Humphrey Visual Field Analyser with the Central 30-2 Threshold Test. Patients' mean age was 68 years. All eyes had visual acuity better than 6/9 with correction, refractive error of less than +/- 7 dioptres, no media opacities and normal pupils (3-6 mm). For all eyes, the frequency of abnormality on the STATPAC Total Deviation (TD) and Pattern Deviation (PD) plots were determined for all individual test points. Mean values and standard deviations were compared. The TD plots represent a composite of both diffuse and localised visual field depression, while PD plots are intended to reflect localised field defects. The frequency of involvement of the test points on the TD plots was higher than on the PD plots (mean +/- SD: 41.5 +/- 11.2% vs 27.5 +/- 10.9%) for all presenting defects. When only deep defects (STATPAC p < 1% and p < 0.5%) were evaluated, TD involvement was still more frequent than the PD (20.1 +/- 9.4% vs 13.2 +/- 7.2%). The topographical pointwise incidence of pure generalised sensitivity loss in the visual field was less frequent when only deep defects were taken into consideration (6.9 +/- 5.7%), and the incidence increased progressively with the inclusion of intermediate and shallow field defects (9.6 +/- 6.8% and 14.0 +/- 8.4% respectively). A component of diffuse sensitivity depression is present at all significant levels of visual field loss in glaucoma. This component of generalised loss decreases as the depth of the field defects increases. This finding suggests that early diffuse field loss converts into well-defined pattern defects at later stages.