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Thomas Georgi, Domagoj Ivastinovic, Martina Brandner, Ralf Hornig, Michaela Velikay-Parel; The influence of visual information on walking behaviour in the Graz Mobility Test. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6951.
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© ARVO (1962-2015); The Authors (2016-present)
One of the challenges in retinal implants is the adequate testing of improvements. In a previous study we introduced the Graz Mobility Test (GMT) and its ability to significantly differentiate subjects with respect to their visual acuity (VA) levels in order to document functional progress in artificial vision. However, at the current stage of development retinal prostheses provide only a rough visual perception and therefore it can be assumed that both visual acuity (VA) and the visual field (VF) are equally essential involved in task performance and orientation. Therefore in this new study we investigated the relation of visual function (VA and VF) and walking behaviour of retinitis pigmentosa (RP) subjects with severe visual impairment.
16 RP volunteers with advanced RP and VA ranging from no light perception (NLP) to counting fingers (CF) passed through four different, structurally similar and relatively short mazes with 11 obstacles of various sizes. Passage time (PT) and number of contacts were measured. A people tracking system with a special designed computer program allowed us to record head scanning movements. The VF was obtained through Goldmann perimetry.
The subjects were devided into two groups according to their visual function. The group A with a VA of light perception or less and a central VF of less 10° had a higher PT, a higher number of contacts and also more head scanning movements per second (SM/sec.) than the group B with a better visual function. All three parameters showed significant differences between both groups (PT: p=0.003; Number of contacts: p=0.003; SM/sec.: p=0.041). Subanalyses revealed a great influence of the localisation of VF scotomas and the frequency of head scanning movements and the number of contacts. Hence patients with an excentric visual field showed less SM/sec.
The parameters of the GMT proved to significantly identify differences of the visual function. The expected visual function with artificial vision will at least approximate that of group B patients and thus results strongly indicate that the benefit of retinal prostheses can be evaluated with the GMT.
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