A Highly-Configurable Full-Field Stimulus Source for Electroretinography

The electroretinogram (ERG) is a functional test widely used in clinical practice to help diagnose diseases of the retina and optic nerve. In fact, it measures the electrical response to a light stimulus of retinal cells, and different ERG tests can be used to probe different retinal areas and cells. The stimulators most commonly used in visual electrophysiology are Ganzfeld stimulators, spherical devices used to perform full-field ERG, and flat monitors, which are not suited for the detection of peripheral early disfunctions, since they do not probe the entire human visual field. Clinical stimulators can use different technologies, but light emitting diodes (LEDs) are becoming very popular since they are almost ideal light sources. Recently, a three dimensional stimulus source based on LEDs able to perform peripheral pattern ERG (ppERG) has been developed. In this paper, a highly-configurable full-field stimulus source for electroretinography based on LEDs is presented. It is capable of presenting an arbitrary pattern of pixels to the entire visual field of a test subject, thus bringing together the functionalities of the existing stimulators. The pattern of pixels is configurable to present stimuli for multiple ERG protocols to any arbitrary sector of the visual field, giving also the possibility to use different colours. The device structure was designed in order to obtain uniform luminance stimuli and minimal light reflection. Moreover, programming and control of the device was widely explored, with a special focus on the development of an electronic design flexible enough to allow the implementation of different ERG protocols. Luminance uniformity of the device was analysed, obtaining satisfactory results. Considering the colour channel of greatest interest for pattern ERG (pERG) protocol, the contrast between black and white checks was much higher than the minimum 80% required by the standards. Finally, the prototyped device was able to elicit consistent flicker ERG and full-field ERG responses in a healthy volunteer subject.