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The topographic relationship between multifocal electroretinographic and behavioral perimetric measures of function
B Fortune1, C A Johnson, G A Cioffi
1Discoveries in Sight Research Laboratories, Devers Eye Institute, Portland, Oregon 97232, USA. bfortune@discoveriesinsight.org
Purpose:
To study the spatial relationship between local functional abnormalities found using multifocal electroretinography (MERG) and those measured using standard automated perimetry (SAP) in a group of glaucoma patients with well-defined, localized visual field loss.
Methods:
MERG's were measured for 15 patients with longstanding, stable, localized SAP visual field loss and for 27 normal controls using VERIS Science (EDI, San Mateo, CA). Most glaucoma patients had substantial asymmetry of visual field defects across the horizontal midline so that within-eye comparisons of MERG changes could be made in addition to comparisons between glaucoma and healthy, aged-matched controls.
Results:
For the glaucoma patient group as a whole, conventional measurements of MERG responses, such as peak-to-trough amplitude, peak implicit time, and scalar-product density, did not reveal abnormalities that spatially corresponded to local sensitivity losses determined by SAP visual field thresholds. Some of the patients had MERG abnormalities (e.g., reduced amplitudes) in areas of advanced SAP visual field loss that indicated local retinal dysfunction. On average, glaucoma patients were missing a MERG component that resembled the optic nerve head component as described by Sutter and Bearse.
Conclusions:
Different MERG components may be affected at different stages of glaucoma, perhaps reflecting a diversity of pathophysiologic mechanisms. This may complicate spatial and temporal relationships between abnormalities found using the MERG and behavioral perimetry, particularly when conventional measurements of MERG responses are used to characterize a diverse patient group/disease.