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Lauren N. Ayton, Robyn H. Guymer, Chi D. Luu; How Blind Is A Flat ERG? - An Improved Method Of Assessing Retinal Function In Patients With Extremely Poor Vision. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5548.
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© ARVO (1962-2015); The Authors (2016-present)
Recent technological advances have led to the development of a number of potential treatments for severe vision loss, including visual prostheses, stem cell transplantation and gene therapy. In order to reliably determine the efficacy of such interventions an accurate assessment of the residual visual function prior to treatment is critical. In this study, we used Discrete Fourier Transform (DFT) to analyse the 30Hz flicker component of the full-field electroretinogram (ERG) to determine the prevalence of patients with residual cone function in a population of patients with a flat ERG.
38 subjects (54 ± 11 years) with advanced stage RP participated in the study. All patients had severe vision loss, either having < 5 degree visual field and/or central vision of hand movements or less. Retinal function was assessed using the full-field ERG according to the International Clinical Electrophysiology of Vision (ISCEV) standard. Retinal responses were recorded using an Espion system and DTL electrodes. Spectral domain optical coherence tomography (OCT) scans were also obtained to examine the retinal ultrastructure. In addition to the conventional ERG reviewing techniques, DFT was used to analyse the 30Hz flicker component of the full-field ERG.
ERG and OCT data were successfully obtained in 75 eyes. Using the conventional ERG reviewing methods, none of the ERG components were detectable in any subjects. Upon Fourier analysis, a 30Hz flicker response was found in 25 of the 75 eyes (33%, 95% CI: 23 - 45%). Of the eyes with a discernable 30Hz flicker response, 40% had a visible photoreceptor layer on OCT. In the eyes with a flat ERG after DFT analysis, only 21.5% had any visible photoreceptor layer.
A significant proportion of subjects with no detectable ERG response on standard analysis were found to have measurable residual retinal function using Fourier analysis method. Many of these subjects did not have an obvious photoreceptor layer on OCT. This study highlights the importance of the development of more intensive visual function assessment tools, in order to accurately capture the true visual ability of people with very low vision prior to any novel intervention. We advocate using DFT as a more complete way to assess residual function in individuals with very low levels of vision.
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