2020–2021 BCSC Basic and Clinical Science Course™
12 Retina and Vitreous
Part I: Fundamentals and Diagnostic Approaches
Chapter 03: Retinal Physiology and Psychophysics
The pattern ERG (PERG) is the retinal response to an isoluminant alternating checker-board stimulus presented to the macula. The stimulus is thus primarily alternating contrast. The responses are small, and signal averaging is needed. However, when technical factors are considered, PERG reliability is similar to full-field ERG. There are 2 main components, P50 and N95, with most subjects showing an earlier negative component, N35. N95 arises in the retinal ganglion cells (RGCs) and thus acts as a direct measure of central RGC function. The P50 component depends upon macular photoreceptor function, even though approximately 70% of it arises in the RGCs; the amplitude of P50 is clinically useful as an objective index of macular function. The image must be in focus on the macula, and PERGs are recorded with electrodes that spare the optics of the eye; contact lens electrodes are not suitable. Because the PERG is evoked by a stimulus similar to that used in recording the visual evoked potential (VEP) (discussed later in this chapter), knowledge of the PERG helps the clinician provide a more accurate interpretation of abnormal VEP findings. PERG is also useful in diagnosing primary ganglion cell disease such as dominantly inherited optic atrophy or Leber hereditary optic neuropathy.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.