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Eduardo Fernandez, Carlos Agullo, Andres Olmedo, Arantxa Alfaro, Antonio Alarcon, Cristina Soto; A Novel Approach for Quantitative Analysis of 3D Phosphenes. Invest. Ophthalmol. Vis. Sci. 2012;53(14):297.
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© ARVO (1962-2015); The Authors (2016-present)
Appropriate delivery of electrical stimulation to visual structures can evoke patterned sensations of light, called phosphenes, in individuals who have been blind for many years. This pivotal finding settled the physiological basis for present efforts to develop a visual prosthesis for the blind. Various methods have been used to document phosphenes, but a standardized methodology is lacking. Here we aim to introduce a novel wireless system and procedure for the documentation and 3D analysis of phosphenes.
Phosphenes were induced by non-invasive Transcranial Magnetic Stimulation (TMS) of occipital cortex. The protocol was applied on a group of 20 sighted and 15 legally blind volunteers. For mapping the visual perceptions we used a wireless system including an autofocus infrared (IR) camera and one IR projector. After each TMS pulse, subjects were asked to make drawings of the perceptions with their own hands (the sensors transmit beams of infrared light allowing 3D hand tracking), with particular emphasis on their localization within the 3D visual field. A customized program allowed easy registration and analysis of collected data.
All study subjects (both healthy and vision impaired) perceived phosphenes and tolerated the procedure without complication. The new mapping technique allows to locate phosphenes in real 3D visual space. Furthermore our procedure allows an easy calculation of the position, volume and area of the subjective perceptions from the coordinates of the drawings.
This new procedure could be used for standardized testing and help to identify suitable candidates that might benefit from a visual neuroprosthetic device as well as for assessments of device efficacy. Furthermore it can be useful for decisions and issues related to visual neuroprosthesis development, patient testing and for studies regarding the physiological organization of human visual system.
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