Abstract
Purpose: :
As visual fields are variable in glaucoma, and there is a suspicion that significant retinal damage can occur prior to visual field loss, alternative methods of detecting glaucomatous damage are needed. We investigated two types of field and compared them to the multifocal pattern electroretinogram (mfPERG), which has the added advantage of providing topographical information.
Methods: :
Six glaucoma patients with mild visual field loss completed four standard (SITA 30-2; S) and four modified (SITA + additional concurrent fixation task; M) visual fields over a mean period of 15.2 months. In a separate session mfPERGs were recorded using a thread electrode without pupil dilatation. Stimuli consisted of 7 hexagons (single centre, six surrounding) with triangular black and white segments in a pin wheel configuration. There was 233ms between each step of the stimulating m-sequence and the triangles reversed at 4Hz. Field threshold, averaged across appropriate neighbouring points, was compared with the N95amplitudes from corresponding areas of the mfPERG using the Spearman rank order test.
Results: :
Mean deviation (averaged over subjects and sessions) was -6.3±5.1dB for S and -6.7±5.4dB for M fields. Using S field data, Spearman Rank correlations were high in one patient and good in two patients (all >0.7); two further patients showed positive correlations (0.4, 0.2). One patient showed a negative correlation (-0.2). The central area of the visual field always correlated well with the corresponding mfPERG area. The five patients with positive correlations exhibited stable field performance over the four fields, while the patient with the negative correlation exhibited evidence of progression (mean deviation -7.32dB to -17.02dB).
Conclusions: :
There was a consistent positive correlation between visual field and mfPERG data in five stable patients. However, as the mfPERG stimulus provided only seven data points, the correlation only reached statistical significance for one patient. Whether the negative correlation in the single progressing patient was related to the progression requires further investigation. We therefore continue to examine the mfPERG in glaucoma to identify features which might indicate future visual field changes.
Keywords: visual fields • electrophysiology: clinical • ganglion cells