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G. Dagnelie, A. K. Ahuja, M. J. McMahon, A. V. Cideciyan, K. G. Locke, Argus II Study Group, R. J. Greenberg; Dark-Adapted Flash Sensitivity Remains Stable Up to 2 Years After ArgusTM II Implantation. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3029.
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To examine the effects of the ArgusTM II retinal implant on remaining native vision in patients with end-stage retinitis pigmentosa.
Using a full-field stimulus test (FST; Roman et al., Exp Eye Res 2005) further developed by Diagnosys (Lowell, MA) for the Espion ColorDomeTM, dark-adapted flash thresholds were collected monocularly in patients with end-stage RP and an Argus II implant in the worse-seeing eye. The test uses a forced-choice yes-no decision paradigm and a modified staircase algorithm to collect probability of seeing data as a function of flash brightness, with the 0 dB point set to 3 cd.s/m². Of 8 patients tested pre-operatively and followed post-operatively at 3 US sites, 6 had pre-op flash thresholds well below the brightness ceiling of the equipment in both eyes. Up to three follow-up measures in each eye were obtained at 3, 6, 9, 12, 18, and 24 months post-op. Thresholds were estimated as the mid-point of the psychometric function.
Psychometric fits to thresholds above 0 dB had wide confidence intervals in some instances; while others diverged due to gradual light adaptation caused by repeated bright flashes. For those tests where thresholds were near or below 0 dB, average within-session threshold variability was 1.4 (range 0.7,2.4) dB in the implanted eye, 1.4 (range 0.5,2.8) dB in the fellow eye. Both within- and between-visit variability increase with mean threshold level, even for threshold levels below 0 dB. For the patients with at least 3 post-op tests, thresholds in implanted and fellow eyes changed by similar amounts between pre-op levels and the most recent values: Implanted eyes changed on average by +2.5 (range -0.7,6.1) dB, fellow eyes by 0.6 (range -4, +6.1) dB; both changes are within the 95% within-session confidence interval. Moreover, implanted and fellow eyes in individual patients tended to fluctuate in conjunction from session to session suggesting systemic rather than eye-specific variability
Using dark-adapted flash thresholds as a measure of residual native vision we conclude that, on average, implanted eyes fare no worse than fellow eyes, supporting the notion that the presence and activity of the Argus II implant has no harmful effect on remaining photoreceptor function in these late-stage RP patients.
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