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Olga Kraszewska, Brian Cichocki, Quentin Davis; Is an electroretinogram in Sudden Acquired Retinal Disorder (SARDS) really flat?. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5339.
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© ARVO (1962-2015); The Authors (2016-present)
Sudden Acquired Retinal Disorder (SARDS) is an idiopathic cause of acute vision loss in dogs and is diagnosed based on the lack of retinal function (as measured with an electroretinogram or ERG), pupil unresponsiveness to red light, normal response to blue light and relatively normal fundus. We examined ERGs obtained from dogs diagnosed with SARDS for information pertinent to the cause and potential treatment of SARDS.
Dogs diagnosed with SARDS were examined in Texas Veterinary Ophthalmology, Fort Worth, TX. The ERGs were performed on dilated and un-sedated animals using stainless steel subdermal needle electrodes (reference and ground) and an ERG-Jet corneal electrode (active). Both scotopic and photopic function were assessed with the RETevet device (LKC Technologies). Six dogs, 7-12 years old, were examined.
Photopic flash and flicker ERG as well as scotopic rod response were not measurable in any of 6 dogs. However, both scotopic mixed stimuli (3.0 cd/s/m2 and 10.0 cd/s/m2) had measurable, but atypical, responses consisting of an a-wave/fast PIII component, followed by the plateau and occasionally a blink. There were no b-waves. A-wave/fast PIII amplitudes varied from 35 to 210 μV and latencies from 55 to 130 ms. Three dogs had similar amplitudes OD and OS; two dogs had amplitudes in one eye around 50% smaller than in the other; and one dog had one eye with a flat ERG while it was measurable in the other.
Some dogs diagnosed with SARDS produce ERGs indicative of ON bipolar cells being blocked, as similar ERG waveforms have been observed in pharmacological studies where 50 μM of a glutamate analog (APB) blocked the b-wave component of the ERG by binding to sites on the postsynaptic membrane. These findings support the glutamate excitotoxicity hypothesis proposed previously as one of the causes of SARDS. Recording ERGs from dogs with SARDS characteristics (7-10 years old, overweight, spayed female of small or mixed breed) not yet diagnosed with this incurable blindness could provide more information about the early stages of the retinal function decline and hopefully provide insight into treatment and prevention.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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