Visual Electrophysiology

Electroretinography, or ERG, focuses on electrical responses generated by retinal cells, whereas visual evoked potentials, or VEPs, assess signals that reach the visual cortex. This distinction allows clinicians to examine different levels of the visual system rather than treating visual dysfunction as a single problem. The comparison can help determine whether abnormal function originates in the retina or along later visual pathways.

The stimulus determines how the visual system is challenged and what electrical response is measured. Controlled flashes produce responses that can be recorded from retinal activity, while patterned visual stimuli can be used when assessing transmission toward the visual cortex. Standardizing the light input makes the resulting voltage changes more suitable for objective evaluation and comparison during clinical testing.

Retinal and cortical measurements examine different stages of visual processing. An abnormal retinal response points toward impaired retinal function, while a VEP finding can indicate disrupted transmission between the eye and visual cortex. Using these measurements together provides functional localization that may be difficult to obtain from symptoms or a standard eye examination alone, particularly when those findings do not explain the patient's visual complaints.

Visual Electrophysiology is particularly valuable when visual symptoms remain unexplained after a standard eye examination. Because the testing provides objective functional evidence, it can help separate retinal disease from optic nerve or cortical dysfunction. This makes it relevant when clinicians need additional information to clarify a diagnosis, assess the likely course of a disorder, or support decisions about treatment.

Testing begins by presenting a controlled flash or patterned visual stimulus and recording the resulting voltage changes with electrodes. The electrode placement depends on the target: retinal responses are assessed for ERG, while scalp potentials are recorded for VEP. The resulting measurements are then interpreted according to the visual structure or pathway being evaluated, rather than by symptoms alone.

The recorded responses provide functional evidence that complements clinical examination. Clinicians can use them to identify whether dysfunction is associated with the retina, optic nerve pathway, or visual cortex, then apply that information to diagnostic assessment. Repeated measurements may also contribute to monitoring inherited or acquired disorders, estimating prognosis, and evaluating whether functional findings support a treatment decision.