Stuart Coupland, PhD, Associate Professor
Clear vision depends on optimal function of each component of the eye’s sensory mechanisms. In response to visual stimuli, the eye’s photoreceptors (rods and cones) create electrical impulses, which are then transmitted via the optic nerve into the visual cortex of the brain. When visual function becomes impaired, electrodiagnostic tests can help pinpoint the source of the malfunction.
In February 1998, the Eye Institute expanded its research and diagnostic capabilities by opening the Visual Electrodiagnostic Laboratory. Under the direction of Dr. Coupland, this facility provides several important measures of retinal function and sensory conduction to assist physicians and patients.
The Electroretinogram (ERG) is especially useful in the early diagnosis of many hereditary eye diseases including retinitis pigmentosa and can be used to determine if family members likely carry the disease gene, which facilitates genetic counseling.
The Visual Evoked Potential (VEP) records brain activity in response to visual stimulation, thereby giving an objective measure of optic nerve function in individuals with diseases such as multiple sclerosis. It also enables physicians to identify damage caused when brain tumours compress visual pathways and assess the impact of neuropsychiatric medications on vision.
The Electrooculogram (EOG) tests the functional integrity of the retinal pigment epithelium (RPE), a thin layer of cells that forms the outer blood-retinal barrier. The RPE supports the function of the photoreceptors and is affected quite early in many hereditary degenerative visual disorders.
In January 2000, multifocal electroretinography (mERG) was introduced for the assessment of central macular function. The multifocal ERG records the focal electroretinal activity from 61 separate regions within the macula which supports central vision. This test is especially useful for assessing patients with central vision problems including age related macular degeneration, diabetic retinopathy, macular holes and macular edema.
In January 2004, the Visual Electrodiagnostic Laboratory incorporated optical coherence tomography (OCT) and scanning laser ophthalmoscope (SLO/OCT) imaging to assess the retinal structural integrity in patients with disease of the macula and/or optic nerve head. These tools provide in vivo exquisite high resolution images of the optic nerve head and macula providing critical information to correlate structure with function. The Laboratory has adopted a new title, Visual Electrodiagnostic Imaging Laboratory, to reflect the fact that we provide high resolution imaging of retinal structure and function.