spektrum der augenheilkunde - 150 Jahre Augenklinik Graz

Abstracts der eingeladenen Vorträgeinto electrical stimulations sent to a stimulator on the tongue is currentlyunder evaluation. The main advantage of this system could beits simplicity (no surgery required) and the potential wide range ofblind patients who could benefit from this technology.Cortical stimulation: Direct electrical stimulation of the occipitallobe produces visual sensations. Recently, our understandingof the functional organization of the human brain has greatlyexpanded due to the development of neuroimaging techniques,mainly functional magnetic resonance imaging (fMRI) that allowdirect noninvasive observation of patterns of brain activity in normalhuman subjects engaged in sensory, motor, or cognitive tasks.In particular, fMRI has been used to chart the retinotopic and functionalorganization of the visual cortex in the human brain. Somestudies using occipital transcranial magnetic stimulations areunder way with mitigated and conflicting results.Optic nerve stimulation: fifteen years ago, a Belgian team publisheda paper “Visual sensations produced by optic nerve stimulationusing an implanted self-sizing spiral cuff electrode” (Brain Res.1998 30;813:181–186) demonstrating that it was theoretically possibleto use the optic nerve when the photoreceptors were destroyed.To our knowledge, this area has not been further developed.Retina stimulation: Since the experimentations done in the‘90s, it has been demonstrated that in degenerative retinal diseasessuch as retinitis pigmentosa or cone-rode dystrophy, evenafter total disappearance of the photoreceptors, the direct stimulationof bipolar or ganglion cells may produce a visual perception inpatients. Two ways to obtain retinal stimulators are explored: preretinalstimulation (Second Sight, Pixium, Epi-Ret project, …) andsubretinal stimulation (Retina Implant).Th e pretinal systems use a picture taken by a camera, processedand sent wirelessly to the stimulator fixed on the eye ball from wherea foil conduct the stimulation at the surface of the retina, enteringthe eye through the sclera at the pars plana. A CE marking and aFDA approval have already been obtained by the first system, theArgus II from Second Sight. This system is able to improve patientmobility outside and allows for some of the patients to read largeletters. The advantages are the relative surgical simplicity of implantation,the possibility given by the image processing (night vision,enhancement of contrast vision, etc.). The disadvantages are thevisual rehabilitation needed after implantation since the stimulatordoesn’t use the natural retinotopy and the fact that the direction ofthe vision is given by the camera, not by the position of the eye.The subretinal implant uses the natural optic of the eye, the “natural”picture stimulating the photodiodes implanted underneaththe macula. A source of external power is nevertheless required andthe subretinal chip is linked to an external power unit through a wiregoing from the subretinal space, through the choroid and the sclerato the orbit and from there to a subcutaneous unit fixed behind theear. A CE marking has been obtained for this device in July 2013 aftertwo clinical studies. The system is able to improve patient mobilityand in a few ones, give spectacular visual results. The advantages arethe use of a more “natural” vision than the epiretinal systems sincethe chip stimulate directly the bipolar cells and a relative simplerehabilitation is required. The main disadvantages are the complexityof surgery, requiring a several hours multidisciplinary operation(ETN and ophthalmologists) and the use of silicone oil to limit therisk of postoperative retinal detachments after implantation.Th e future: The extra-optical stimulations systems are promisingthanks to their relative simplicity, the wide spectrum of blindpatients who could benefit from this technology and the non surgicalapproach, limiting the risk of complications. Nevertheless, theperformances are probably limited and the easiness of use has tobe demonstrated.Th e direct cortical stimulation is far away of reaching humanclinical studies but remains an interesting way for research.The ideal retinal stimulator, limited to patients who have lostsight because of a degeneration of photoreceptors, should probablybe subretinaly implanted. The preretinal stimulator is limited by thenumber of electrodes (50–60 currently) and it would be difficult tohave more than 100–200 electrodes if each one needs its own wire,resulting in an unacceptable size of the intraocular foil. A subretinalimplant should be totally wireless making surgery relatively easy.The stimulation should be powerful enough to stimulate autonomousphotodiodes under the retina, using either infrared or laserbeam, guided by a processor. The number of photodiodes couldbe almost unlimited since it could be implanted in several sheetsand therefore could cover the whole posterior pole. This implant isalready tested in animal models.Visual perception in artificial visionMichaela Velikay-Parel, Thomas Georgi, Alex Kreilinger,Andreas Wedrich, GrazRetinal implant systems generate electrical pulses, and thus producevisual perception. To understand how the electrical stimulationis transformed into visual perception, numerous in vitrostudies have been performed and the subject is still under investigation.At the current stage of development artificial vision providesonly a rough visual perception and the fragmentary perception ofthe artificial vision makes visual function testing more approximatea task performance, where visual acuity is as important as the visualfield for daily life activities. Since in regular ophthalmologic testingis not applicable to display improvements with the implant, a numberof tests have been invented to provide the adequate testing orultimately show advantages in between the two technologies. Thetest battery includes standardized psychophysical laboratory tests,the subjects’ own and objective reports of daily living activities andobservations of their indoors and outdoors performance.Recently the results of clinical studies on retinal implants havebeen published and display the adequacy of the tests and its relevancefor the daily life activities. Two thirds of the patients experiencedvision improvement, of which half reached a substantialvision gain.On the basis of these clinical studies authorities in the EU andUSA decided to excepted retinal implants as clinical therapy.1 3Festtagung 150 Jahre Universitäts-Augenklinik Graz 325