The very large electrode array for retinal stimulation (VLARS)-A concept study.

OBJECTIVE: The restoration of vision in blind patients suffering from degenerative retinal diseases like retinitis pigmentosa may be obtained by local electrical stimulation with retinal implants. In this study, a very large electrode array for retinal stimulation (VLARS) was introduced and tested regarding its safety in implantation and biocompatibility. Further, the array's stimulation capabilities were tested in an acute setting. APPROACH: The polyimide-based implants have a diameter of 12 mm, cover approximately 110 mm2 of the retinal surface and carrying 250 iridium oxide coated gold electrodes. The implantation surgery was established in cadaveric porcine eyes. To analyze biocompatibility, ten rabbits were implanted with the VLARS device, and observed for 12 weeks using slit lamp examination, fundus photography, optical coherence tomography (OCT) as well as ultrasound imaging. After enucleation, histological examinations were performed. In acute stimulation experiments, electrodes recorded cortical field potentials upon retinal stimulation in the visual cortex in rabbits. MAIN RESULTS: Implantation studies in rabbits showed that the implantation surgery is safe but difficult. Retinal detachment induced by retinal tears was observed in five animals in varying severity. In five cases, corneal edema reduced the quality of the follow-up examinations. Findings in OCT-imaging and funduscopy suggested that peripheral fixation was insufficient in various animals. Results of the acute stimulation demonstrated the array's ability to elicit cortical responses. SIGNIFICANCE: Overall, it was possible to implant very large epiretinal arrays. On retinal stimulation with the VLARS responses in the visual cortex were recorded. The VLARS device offers the opportunity to restore a much larger field of visual perception when compared to current available retinal implants.

Role of the Endothelial Layer in the Deswelling Process of Organ-Cultured Human Corneas Before Transplantation.

PURPOSE: Before corneal transplant surgery, a deswelling process of organ-cultured corneas is required. This study compares the deswelling kinetics of corneas with an intact endothelial cell layer and disrupted or removed endothelium by measuring central corneal thickness (CCT) over time using anterior segment spectral domain optical coherence tomography. METHODS: Ten donor pairs were cultured in organ culture. The right and left corneas were alternately assigned to one of 2 deswelling groups. Deswelling in the first group [endothelial group (EG)] was induced using a medium with dextran 5%. Corneas of the second group [nonendothelial group (NEG)] were deprived of their endothelial cell layer by trypsinization and were then placed in the same deswelling medium. CCT (mean ± SD) was measured by anterior segment spectral domain optical coherence tomography before deswelling (0 hours) and after 1, 2, 3, 6, 12, 24, 48, 72, and 144 hours. Deswelling kinetics was analyzed through the nonlinear platform in SAS/JMP11 Pro. RESULTS: Before deswelling, CCT was 1071.0 µm (±129.6 µm) and 1133.8 µm (±124.3 µm) in the EG and NEG, respectively. Minimum corneal thickness was obtained after 24 hours in the EG (531.9 ± 47.5 µm) and 6 hours in the NEG (645 ± 81.2 µm). CCT was significantly (P < 0.01) higher in the NEG than EG after more than 6 hours. CONCLUSIONS: Corneal dehydration after organ culture seems to be a multifactorial process, which not only depends on osmotic effects of the deswelling compound but also requires the presence of an intact endothelial cell layer.

Gebauer SLc Original and Moria One-Use Plus automated microkeratomes for ultrathin Descemet's stripping automated endothelial keratoplasty preparation.

PURPOSE: We compared the SLc Original (SLc) and One-Use Plus (OUP) microkeratomes for ultrathin Descemet's stripping automated endothelial keratoplasty (DSAEK) lamella preparation and storage, vis-à-vis accuracy, endothelial cell loss (ECL) and lamellar surface roughness (LSR). METHODS: Twenty-five human corneas were dissected with single-use heads of different sizes aiming for a posterior lamella (PL) thickness of 85 µm, after which they were incubated for 6 days in a 5% dextran medium. Before preparation (0 hr) and 1, 24, and 144 hr after dissection, ECL and corneal thickness (CCT) were measured by ultrasound pachymetry (USP) and optical coherence tomography (OCT). Lamellar surface roughness (LSR) was assessed by scanning electron microscopy (SEM) and evaluated by two masked observers. RESULTS: Prior to cutting, CCTs did not differ between OCT and USP measurements, with a high correlation between the two modalities (r2  = 0.8; p < 0.0001). Both systems succeeded in UT lamella preparation (CCT 40-130 µm) in 88% of cases. The OUP heads cut significantly deeper than the according SLc counterparts (p = 0.001), while the variance did not differ. The mean PL thickness increased significantly in the following incubation period (p = 0.01) with no difference between the keratome groups. Endothelial cell density (ECD) decreased significantly from before to 1 hr after preparation (-5.6%; p = 0.04), with no changes in the following 144-hr incubation period and no differences between the OUP and SLc group. Lamellar surface roughness (LSR) did not differ between both systems. CONCLUSIONS: The SLc and the OUP system are both suited for the preparation of UT-DSAEK lamellae. Neither system differed significantly in variability, LSR or ECL, which did not increase during a 6-day incubation period.