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Thomas Wright, Josefin Nilsson, Michelle McFarlane, Carol Westall; A potential S-Cone dominated ERG response shows robust delays in Type 1 diabetes.. Journal of Vision 2009;9(14):78. doi: https://doi.org/10.1167/9.14.78.
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“Introduction: The short wavelength visual pathway has been shown to be particularly sensitive to systemic insult. Diabetic retinopathy is a common outcome of diabetes. The short wavelength visual pathways are disrupted early in the disease. Clinically Diabetic Retinopathy manifests as pathology to the vascular and neuronal structures of the retina. Once the retinopathy becomes clinically visible it is irreversible and if left untreated can lead to vision loss. Early detection of retinal pathology is essential for successful management and treatment of the disease process. The short wavelength electroretinogram (sERG) is the retinal signal generated from stimulation of the short wavelength sensitive cones (s-cones). Currently potentials of only a few microvolts are isolated making current testing protocols challenging to use in a clinical situation. This paper presents a protocol for isolating a robust s- cone dominated ERG response. This response shows a clear delay in timing from patients with Type 1 diabetes before clinical evidence of clinically visible retinopathy.
Methods: Our s-cone targeting ERG protocol consists of relatively low intensity (80 td.s/m2) short wavelength (425nm) flashes presented to a light adapted eye. ERGs were performed using an Espion colordome ERG system (Diagnosys LLC) and responses recorded using bipolar Burian-Allen contact lens electrodes (Hanson). 13 adolescents with type 1 diabetes have been recruited from the endocrinology clinic at the Hospital for Sick Children. Thirteen age similar subjects without diabetes served as controls. A subset of patients (N=6) and controls (N=7) have also been tested with the ISCEV standard Light-adapted 10 cd stimulus that primarily isolates a response from the long- medium cone (LM-cone) visual system. Visual acuity (ETDRS); contrast sensitivity (Pellie-Robson) and color vision (minimalist) were tested in all participants. In addition all subjects received either a dilated fundus examination or 7 field fundus photography to detect retinal pathology, patients with pathology were excluded from further analysis. As short term blood glucose levels are known to affect the ERG, these were monitored and controlled during the test procedures.
Results: Psychophysical vision testing showed no significant differences between the groups. In control subjects the s-cone targeted ERG elicited a response with a small negative a-wave component, followed by relatively slow positive b-wave component(40.9 ms ± 3.4ms). The response from subjects with diabetes had a similar morphology but with a significantly delayed implicit time (45.9 ms ± 3.7ms; p”
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