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author:("d'cruz, L")
1.  Factors Affecting Perceptual Threshold in Argus II Retinal Prosthesis Subjects 
Purpose
The Argus II epiretinal prosthesis has been developed to provide partial restoration of vision to subjects blinded from outer retinal degenerative disease. Participants were surgically implanted with the system in the United States and Europe in a single arm, prospective, multicenter clinical trial. The purpose of this investigation was to determine which factors affect electrical thresholds in order to inform surgical placement of the device.
Methods
Electrode–retina and electrode–fovea distances were determined using SD-OCT and fundus photography, respectively. Perceptual threshold to electrical stimulation of electrodes was measured using custom developed software, in which current amplitude was varied until the threshold was found. Full field stimulus light threshold was measured using the Espion D-FST test. Relationships between electrical threshold and these three explanatory variables (electrode–retina distance, electrode–fovea distance, and monocular light threshold) were quantified using regression.
Results
Regression analysis showed a significant correlation between electrical threshold and electrode–retina distance (R2 = 0.50, P = 0.0002; n = 703 electrodes). 90.3% of electrodes in contact with the macula (n = 207) elicited percepts at charge densities less than 1 mC/cm2/phase. These threshold data also correlated well with ganglion cell density profile (P = 0.03). A weaker, but still significant, inverse correlation was found between light threshold and electrical threshold (R2 < 0.52, P = 0.01). Multivariate modeling indicated that electrode–retina distance and light threshold are highly predictive of electrode threshold (R2 = 0.87; P < 0.0005).
Conclusions
Taken together, these results suggest that while light threshold should be used to inform patient selection, macular contact of the array is paramount.
Translational Relevance
Reported Argus II clinical study results are in good agreement with prior in vitro and in vivo studies, and support the development of higher-density systems that employ smaller diameter electrodes. (clinicaltrials.gov identifier: NCT00407602)
doi:10.1167/tvst.2.4.1
PMCID: PMC3763895  PMID: 24049718
retinal prosthesis; retinal degeneration; retinitis pigmentosa
2.  Blind subjects implanted with the Argus II retinal prosthesis are able to improve performance in a spatial-motor task 
Background/aims
To determine to what extent subjects implanted with the Argus II retinal prosthesis can improve performance compared with residual native vision in a spatial-motor task.
Methods
High-contrast square stimuli (5.85 cm sides) were displayed in random locations on a 19″ (48.3 cm) touch screen monitor located 12″ (30.5 cm) in front of the subject. Subjects were instructed to locate and touch the square centre with the system on and then off (40 trials each). The coordinates of the square centre and location touched were recorded.
Results
Ninety-six percent (26/27) of subjects showed a significant improvement in accuracy and 93% (25/27) show a significant improvement in repeatability with the system on compared with off (p<0.05, Student t test). A group of five subjects that had both accuracy and repeatability values <250 pixels (7.4 cm) with the system off (ie, using only their residual vision) was significantly more accurate and repeatable than the remainder of the cohort (p<0.01). Of this group, four subjects showed a significant improvement in both accuracy and repeatability with the system on.
Conclusion
In a study on the largest cohort of visual prosthesis recipients to date, we found that artificial vision augments information from existing vision in a spatial-motor task.
Clinical trials registry no
NCT00407602.
doi:10.1136/bjo.2010.179622
PMCID: PMC3345188  PMID: 20881025

Results 1-2 (2)