Sean Caffey

Advances in the development of visual prostheses.

Visual prostheses are based on neuronal electrical stimulation at different locations along the visual pathway (ie, cortical, optic nerve, epiretinal, subretinal). In terms of retinal prostheses, advances in microtechnology have allowed for the development of sophisticated, high-density integrated circuit devices that may be implanted either in the subretinal or epiretinal space. Analogous to the cochlear implants for some forms of deafness, these devices could restore useful vision by converting visual information into patterns of electrical stimulation that would excite the remaining spared inner retinal neurons in patients with diseases such as retinitis pigmentosa and age-related macular degeneration. The different types of implants and recent results are discussed, but special emphasis is given to retinal implants.

Effects of radiofrequency energy on human articular cartilage: an analysis of 5 systems.

Background Previous radiofrequency work has not rigidly controlled energy application to the articular cartilage, giving uncertain results published to date. Hypothesis At minimal settings, radiofrequency probes cause cell death in measurable areas when applied to human articular cartilage. Study Design Controlled laboratory study. Methods Simulating operating room conditions, 5 commercially available radiofrequency probes were attached to a customized jig to standardize a minimal contact pressure of each probe tip to 2.0 g. Keeping all variables the same, probes were placed on specific points of fresh grade II human cartilage with treatment times of 1 and 3 seconds at the manufacturers recommended settings. Grade III cartilage was also tested with a treatment time of 3 seconds, and grade II cartilage was studied with the probe held 1 mm off the cartilage surface. Cartilage was blindly analyzed by confocal microscopy using a live/dead cell viability assay to determine the extent of cell death. Results Radiofrequency probes produced significant cellular death in the form of a half-circle into the cartilage to variable depths. For treatment times of 1 and 3 seconds, cell death measurements ranged from 404 to 539 μm and 1034 to 1283 μm, respectively. One probe failed to show any effect, with minimal evidence of cell death or cartilage smoothing. When probes were kept a 1.0-mm distance above the cartilage, no cell death or cartilage smoothing was noted. Radiofrequency treatment of grade III cartilage penetrated to the subchondral bone. There was no statistically significant difference between the damage caused by monopolar and bipolar probes when tested under these rigidly controlled conditions. Conclusion These results showed significant cellular death at these minimal conditions to the underlying chondrocytes with radiofrequency probes. Surgeons using this technology need to be aware of the power and dangerous potential these probes can have on articular cartilage.

Angiographic characteristics in patients undergoing macular translocation for subfoveal choroidal neovascularization secondary to age-related macular degeneration.

Purpose To review in a standardized fashion pre- and postoperative fluorescein angiographic characteristics in patients undergoing limited macular translocation (LMT) with scleral imbrication to treat subfoveal choroidal neovascularization (SFCNV) secondary to age-related macular degeneration (AMD). The current study was undertaken to assess any potential effects of the translocation procedure on altering the angiographic characteristics of SFCNV before laser photocoagulation. Methods A consecutive series of patients undergoing LMT for AMD was identified retrospectively. The pre- and postoperative fluorescein angiograms were reviewed in a masked fashion. Angiographic characteristics evaluated included pre- and postoperative lesion components, stability of lesion, and the amount of retinal translocation obtained. Results Eighty-eight patients (90 eyes) had angiograms of adequate quality to permit evaluation. Time between the preoperative and the prelaser angiogram ranged from 2 to 84 days (median 7.5 days). Neovascular complexes remained unchanged or decreased in size in 79% of patients. There was no statistically significant difference in lesion size between the pre- and postoperative periods (P = 0.34). Retinal movement ranged from 160 &mgr;m to 3,320 &mgr;m (median 960 &mgr;m), with 61% of cases undergoing effective translocation (i.e., the fovea was moved away from the neovascular complex). None of the lesion components or demographic factors evaluated affected the amount of translocation obtained. Larger lesions were more likely to remain subfoveal following translocation (P = 0.004). Conclusion The size and lesion characteristics appear relatively stable following translocation. Amount of retinal movement is not associated with angiographic lesion characteristics. Only size was associated with achievement of desired translocation in the final model, with large lesions being less likely to achieve desired translocation. In our study group, the amount of retinal translocation was variable with 61% of cases undergoing effective translocation.