title: The use of Argus® II retinal prosthesis by blind subjects to achieve localisation and prehension of objects in 3-dimensional space.
abstract: BACKGROUND
  The Argus® II retinal prosthesis system has entered mainstream treatment for patients blind from Retinitis Pigmentosa (RP). We set out to evaluate the use of this system by blind subjects to achieve object localisation and prehension in 3-dimensional space.
  
  
  METHODS
  This is a single-centre, prospective, internally-controlled case series involving 5 blind RP subjects who received the Argus® II implant. The subjects were instructed to visually locate, reach and grasp (i.e. prehension) a small white cuboid object placed at random locations on a black worktop. A flashing LED beacon was attached to the reaching index finger (as a finger marker) to assess the effect of enhanced finger visualisation on performance. Tasks were performed with the prosthesis switched "on" or "off" and with the finger marker switched "on" or "off". Forty-eight trials were performed per subject. Trajectory of each subject's hand movement during the task was recorded by a 3D motion-capture unit (Qualysis®, see supplementary video) and analysed using a MATLAB script.
  
  
  RESULTS
  Percentage of successful prehension±standard deviation was: 71.3 ± 27.1 % with prosthesis on and finger marker on; 77.5 ± 24.5 % with prosthesis on and finger marker off; 0.0 ± 0.0 % with prosthesis off and finger marker on, and 0.00 ± 0.00 % with prosthesis off and finger marker off. The finger marker did not have a significant effect on performance (P = 0.546 and 1, Wilcoxon Signed Rank test, with prosthesis on and off respectively). With prosthesis off, none of the subjects were able to visually locate the target object and no initiation of prehension was attempted. With prosthesis on, prehension was initiated on 82.5 % (range 59-100 %) of the trials with 89.0 % (range 66.7-100 %) achieving successful prehension.
  
  
  CONCLUSIONS
  Argus® II subjects were able to achieve object localisation and prehension better with their prosthesis switched on than off.
authors.affiliation: Biomedical Research Centre, National Institute of Health Research, Moorfields Eye Hospital NHS Foundation Trust, 162 City Road, London, EC1V 2PD, UK. h.luo.96@cantab.net.|Institute of Ophthalmology, University College London, 11-43 Bath Street, London, EC1V 9EL, UK. h.luo.96@cantab.net.|Vitreoretinal Service, Moorfields Eye Hospital NHS Foundation Trust, 162 City Road, London, EC1V 2PD, UK. h.luo.96@cantab.net.
authors.forename: Yvonne Hsu-Lin
authors.initials: YH
authors.lastname: Luo
authors.affiliation: Biomedical Research Centre, National Institute of Health Research, Moorfields Eye Hospital NHS Foundation Trust, 162 City Road, London, EC1V 2PD, UK.
authors.forename: Joe Jianjiang
authors.initials: JJ
authors.lastname: Zhong
authors.affiliation: Biomedical Research Centre, National Institute of Health Research, Moorfields Eye Hospital NHS Foundation Trust, 162 City Road, London, EC1V 2PD, UK.|Institute of Ophthalmology, University College London, 11-43 Bath Street, London, EC1V 9EL, UK.
authors.forename: Lyndon
authors.initials: L
authors.lastname: da Cruz
mesh_terms: D000368:Aged; D001766:Blindness / Q000503:physiopathology* / Q000534:rehabilitation; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D010364:Pattern Recognition, Visual / Q000502:physiology*; D011434:Proprioception / Q000502:physiology*; D011446:Prospective Studies; D019919:Prosthesis Implantation; D011597:Psychomotor Performance / Q000502:physiology*; D011603:Psychophysiology; D012160:Retina / Q000503:physiopathology*; D012174:Retinitis Pigmentosa / Q000503:physiopathology* / Q000534:rehabilitation; D057488:Visual Prosthesis
keywords: Artificial retina; Outer retinal degeneration; Psychophysical testing; Retinal prosthesis; Retinitis pigmentosa