Aled Evans

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BACKGROUND A new technique exists that enables functional mapping of the retina. A control population was examined to obtain normative values and to assess the reproducibility of this new test. METHODS Twenty healthy volunteers were tested using a 61 hexagonal array stimulus with a 14 minute recording period. Median 5th and 95th percentiles were(More)
Classical electromagnetic theory is used to examine the topographical variation in electrical potentials over the corneal surface resulting from specific retinal stimuli. Results from a three-dimensional mathematical model show that over 97% of calculated electromagnetic field potentials lie within 3% of previous analytical model data for an axially(More)
The effect of filter bandwith on the multifocal electroretinogram was assessed by means of theoretical calculation, electronic simulation and real multifocal electroretinogram recordings. Waveform distortion by high-pass filtering on simulated square waves, normal electroretinogram waveforms and negative electroretinogram waveforms was demonstrated. The(More)
Functional mapping of the retina by multifocal electroretinographic recordings is now possible. We compared the normal range, repeatability and response topography of this new technique with conventional static Humphrey perimetry to assess its suitability in clinical practice. The multifocal technique was performed on 60 age-matched controls. Measures of(More)
The purpose of this paper is to compare and evaluate the multifocal ERG response from raster based CRT and Digital Projection (LCD) stimulus delivery systems. A custom built p.c. based multifocal system was used to generate a 61 hexagonal element stimulus array. The stimulus was presented on a high luminance CRT display and on a back projected screen using(More)
There are a wide range of variables which can influence the quality of the multifocal response. It is possible to place these variables into one of four categories. First, the method of stimulus delivery will determine the field of view, interference levels and the duration of on-state stimulation. Second, data acquisition variables such as electrode type(More)
There are a number of variables which can influence the quality of multifocal ERG waveforms. In common with visual field measurements, fixation quality may be an important parameter on the integrity of the acquired data. A low cost, fixation-monitoring device was used to assess fixation quality on a group of normal volunteers. Data was successfully acquired(More)
PURPOSE To determine the features of wide-field multifocal electroretinography (WF-mfERG) recorded in patients with central retinal vein occlusion (CRVO) and to compare WF-mfERG responses of the affected and fellow eyes. In addition, WF-mfERG responses were also compared by using standard electroretinography (ERG). METHODS WF-mfERG and ERG responses were(More)
The purpose of this paper is to provide the reader with a better insight into the mechanisms of multifocal ERG (mfERG) recording. The construction of the first and second order mfERG responses were examined by recovering the response to specific pulse trains embedded in the m-sequence.A custom built pc based multifocal system driving a LED stimulator was(More)