Pattern ERG (PERG)
The Pattern ERG (pERG) produces a macular retinal ganglion cell response. When done as a follow-up to an abnormal pattern VEP, the pERG can elucidate whether the abnormality is caused by retinal or optic nerve dysfunction. This test may also assist in diagnosing glaucoma, optic neuropathies, and primary ganglion cell diseases.
A pERG can be done using either the Diagnosys 27” Monitor or the Envoy stimulators. Our monocular Envoy stimulator protocol totals four steps, a checkerboard and bar pattern for the right eye, and then repeats for the left. Diagnosys does both because the bar pattern is more tolerant to lateral eye movements. The 27” LCD monitor tests a patient binocularly and uses a 1.0-degree checkerboard stimulus.
The P50 and N95:P50 ratio both reflect macular retinal ganglion cell function and depend upon healthy macular cones. When the P50 alone is reduced or delayed, macular dysfunction is suspected, while a reduction of N95 with preservation of P50 suggests dysfunction of retinal ganglion cells.
A normal pattern ERG response with P50 at 48ms and P95 close to 90ms.
Bach M, Brigell MG, Hawlina M, Holder GE, Johnson MA, McCulloch DL, Meigen T, Viswanathan S (2013) ISCEV standard for clinical pattern electroretinography (PERG) – 2012 update. Doc Ophthalmol 126:1–7