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).

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.

Intravitreal anti-VEGF treatment in eyes with combined choroidal neovascularisation and vitreomacular traction syndrome.

PURPOSE: To report the effect of intravitreal anti-vascular endothelial growth factor injections (IVI) on visual acuity in eyes with choroidal neovascularisation (CNVM) and co-existent vitreomacular traction (VMT) or when VMT has developed during the course of treatment. METHODS: Retrospective interventional case series of seven eyes in seven patients. VMT was monitored with serial optical coherence tomography scans. RESULTS: The mean age at presentation was 74 years (range 64-95 years). All patients presented with blurring of central vision, rather than distortion. The aetiology of CNVM was wet age-related macular degeneration in five eyes (72%), angioid streaks in one eye (14%) and pathological myopia in one eye (14%). Ranibizumab was used in four eyes (57%) and bevacizumab in three (43%) for the active CNVM component. The mean follow-up was 11 months (range 2-28 months). None of the eyes in this series required surgery for the VMT component, nor were there any cases of spontaneous resolution of VMT. Visual acuity was stabilised or improved in five of the seven eyes (71%) with IVI. Visual acuity results across the whole group were gain of three or more lines of Snellen visual acuity in two eyes (28%), gain of up to three lines in three eyes (42%), no change in visual acuity in one eye (14%) and loss of up to three lines in one eye (14%). There were no eyes losing more than three lines of Snellen visual acuity. In four eyes with pre-existing VMT, visual acuity improved in three with IVI. In three eyes that developed VMT after IVI, visual acuity improved in two with IVI. Delay from diagnosis of CNVM to treatment with IVI contributed to a poor response. CONCLUSIONS: Most eyes improved visual acuity with IVI for combined CNVM and VMT. Despite the often dramatic features of VMT on optical coherence tomography, treatment of co-existing CNVM should be prompt. Vitreoretinal surgery was not required in this series, but is held in reserve if there is still potential for gain in vision following CNVM resolution.