Pattern electroretinogram in glaucoma

Abstract

Purpose of review-Several studies have shown that the pattern electroretinogram, a direct, objective method of measuring retinal ganglion cell function, is altered early in ocular hypertension and glaucoma. Renewed interest in the pattern electroretinogram for early detection of pre-perimetric glaucoma has been sparked by noninvasive and reproducible methods of recording using skin electrodes.Recent findings-With the noninvasive pattern electroretinogram, response abnormalities have been detected in up to 50% of glaucoma suspects with normal standard perimetry. In early glaucoma (with either normal or high intraocular pressure), a reduction of intraocular pressure has sometimes yielded improvement in pattern electroretinogram amplitude. A prolonged steady-state stimulus presentation reduces the pattern electroretinogram amplitude and increases optic nerve blood flow in normal subjects, suggesting that sustained activity of retinal ganglion cells is physiologcally associated with autoregulatory changes of the neuralvascular system. It is unknown whether this autoregulation is altered in glaucoma. The multifocal pattern electroretinogram does not seem to have an advantage over the pattern electroretinogram in the early detection of glaucoma. The photopic negative response of the diffuse flash electroretinogram has shown changes in glaucoma, but may not be able to detect retinal dysfunction in normal tension glaucoma.Summary-The pattern electroretinogram is a noninvasive, direct, objective method that may be useful to clinicians in detecting early retinal ganglion cell dysfunction in glaucoma suspects. The pattern electroretinogram may also optimize treatment strategies based on improvement of retinal ganglion cell function. Keywords

Progressive Loss of Retinal Ganglion Cell Function Precedes Structural Loss by Several Years in Glaucoma Suspects

“…It is known that the PERG signal may become reduced early in glaucoma. 2,3 As it approaches the bottom of its dynamic range (see Methods), there is progressively less room left for further reduction. Therefore, the slope of PERG amplitude progression will decrease with decreasing baseline amplitude.…”

“…PERG is thought to be abnormal before any structural abnormality is observed. 2,3 It has been proposed that abnormality in the PERG indicates dysfunction predating cell death and, thus, would signal a suitable time for intervention.…”

“…[2][3][4][5][6][7] Recent studies in human and mouse models of glaucoma have shown that in the early stages of the disease the magnitude of loss of PERG signal exceeds that expected from loss of RGC axons. 5,6,8 This implies the presence of a population of viable, but dysfunctional RGC.…”

The role of pattern-reversal electroretinography in the diagnosis of glaucoma

“…However, it has also been suggested that the PERG response reflects diffuse and non-focal damage to ganglion cells, i.e., pan-retinal ganglion cell damage (101) . According to Ventura et al, when a patient with glaucoma without perimetric defect exhibits changes in the PERG response (Figure 2), the abnormality indicates generalized RGC dysfunction; while the PERG response is normal in a glaucoma patient with VF defect, perimetry detects peripheral focal field loss in a patient with near-nor mal RGC function (100) . Although a correlation between glaucomatous VF defects and reduced PERG amplitude in the corresponding hemifield has already been reported (41) , it is important to remember that standard PERG is not appropriate for the detection of focal glaucomatous damage (102) .…”

“…While PERG is an objective test and represents a mass response of the central retina, perimetry is a subjective examination based on focal threshold stimulus of the central and peripheral retina (100) . However, it has also been suggested that the PERG response reflects diffuse and non-focal damage to ganglion cells, i.e., pan-retinal ganglion cell damage (101) .…”