Eyeworld

EW NEWS & OPINION October 2015 19 by Farrell "Toby" Tyson, MD systems between the eye and the brain. However, most ophthalmol- ogists' armamentariums include a variety of diagnostic modalities that almost all focus on the eye. Those that do focus on the whole process of interpretation of an image, such as visual acuity, Humphrey visual fields, and Amsler grids, are sub- jective and considered less reliable. Electrophysiology, on the other hand, provides objective analysis of the entire neuro-visual pathway in- cluding visual function, locality, and severity for diagnosis and treatment. VEP measures the amplitude and latency of electrical activity throughout the pathway of the visual cortex. Standard VEP testing uses predetermined pattern-reversal stimuli consisting of high contrast and low contrast checkerboards and then tracks the electrical activity generated from the retina to the visual cortex. It does not rely on any kind of active patient participation, making it the only objective, func- tional measurement of the entire visual system. PERG testing is similar to VEP testing, but focuses on activity in the retinal ganglion cells. Glaucoma, Physician shares how office-based electrophysiology visual evoked potential and pattern electroretinography testing allow him to make a more exact diagnosis A s a comprehensive ophthalmologist, I often see patients at the start of their journey into deteriorating vision. One of the most important services I can provide for these patients is a differential diagnosis and guidance on how they should proceed with their vision care. I have found that office-based electrophysiology visual evoked potential (VEP) and pattern electroretinography (PERG) testing (Diopsys NOVA, Pine Brook, N.J.) allows me to make a more exact diagnosis and recommend the best treatment options to my patients. VEP and PERG testing Human vision is the amalgamation of numerous different functional Electrophysiology in the clinic continued on page 20 Normal ERG vision test Normal VEP vision test Source: Diopsys Inc. for example, is characterized by pro- gressive loss of retinal ganglion cells and their axons. Both VEP and PERG have proven effective at detecting early disease. 1 A recently published study found that abnormalities in- dicating disease in PERG testing pre- ceded detection of disease via optical coherence tomography of the retinal nerve fiber layer by approximately 8 years. 2 This is a significant finding to help preserve vision in patients at risk of progressive vision loss from glaucoma. In fact, several studies support the ability of PERG testing to detect the amount of damage to retinal ganglion cells early enough to allow viable cells to be restored. 3,4,5 This presents a huge change in the way we approach glaucoma to minimize functional loss and its effects on vision. Clinical use We purchased the Diopsys NOVA Vi- sion Testing System and have found it very easy for all of our technicians to use correctly. The test results are easy to interpret and very helpful in our diagnosis and treatment of pa- tients. Technological developments by Diopsys have also resulted in non-invasive sensors, faster testing time and improved data collection, making electrophysiology a practical tool for office use. It is often difficult to determine treatment for patients with ocular hypertension. Visual field tests, if reliable, do not show abnormalities until nearly 30% of the optic nerve is irreversibly damaged. OCT visual- ization of the nerve fiber layer may pick up damage earlier, but many patients with ocular hypertension show no changes or only border- line pathology on OCT. If I have a patient with OHT and a normal appearing optical nerve, I want PERG testing using both high and low contrast so that I can determine if this is just an individual with a naturally higher IOP or a patient in the earliest stages of retinal dysfunc- tion. For patients with known glauco- ma, PERG testing provides an excel- lent measurement of disease status for patients in treatment. I then re- peat the testing as needed to analyze whether the results of our treatment

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