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S. Mehta, M. A. Brantley, Jr.; Correlation of Glaucoma Severity With Reduction in the Amplitude of the Photopic Negative Response of the Electroretinogram. Invest. Ophthalmol. Vis. Sci. 2007;48(13):214.
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To determine whether reduction in the amplitude of the photopic negative response (PhNR) of the electroretinogram (ERG) correlates with the amount of visual field loss in primary open angle glaucoma (POAG).
ERGs were recorded in 9 eyes from 5 normal patients (21 to 80 years), 4 eyes from 3 POAG patients (61 to 80 years) with early visual field loss (mean deviation <6 DB) on Humphrey 24-2, and 5 eyes from 3 POAG patients (64-86 years) with moderate to advanced visual field loss (mean deviation ≥6 DB). Brief (<6 ms) full-field red Ganzfeld flashes (1.7 log phot td.s) were delivered on a rod-saturating blue background (3.7 log phot td.s) using a handheld Ganzfeld stimulator. Responses were detected using DTL electrodes and analyzed using the Espion ERG system.
Control eyes had a mean PhNR amplitude (MPA) of -27.72 with a standard deviation (SD) of 4.81. Eyes with early glaucomatous field loss (average mean deviation = 2.87) had an MPA of -22.27 (SD = 5.64). Eyes with moderate to advanced glaucomatous field loss (average mean deviation = 22.45) had an MPA of +2.23 (SD = 4.14). A-wave amplitudes, B-wave amplitudes, and PhNR implicit times remained relatively constant throughout the study regardless of the severity of field loss. In two patients with asymmetric glaucoma who had low reliability scores on HVF testing, the reduction in PhNR amplitude correlated well with severity of disease.
There is a clear and marked reduction of the PhNR amplitude in eyes with moderate to advanced visual field loss from glaucoma. The eyes with early visual field loss displayed a reduced mean PhNR response, although this did not reach statistical significance. The PhNR provides a rapid, objective method of measuring optic nerve function that may be particularly helpful in evaluating severity of glaucomatous damage in patients who have difficulty with visual field testing.
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