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SR Montezuma, JF Rizzo, OR Ziv; Differential Recovery of ERG and VEP Following Vitreoretinal Surgery: Implications for Acute Testing of an Implanted Retinal Prosthesis . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4477.
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Purpose: Surgical introduction of a retinal prosthesis could cause mechanical damage to the implant or retina, or the saline environment of the eye could damage the microelectronics. Hence, it is desirable to test the device and retinal function following implantation. In animals biological function can be tested by performing an ERG or VEP. This study examines the usefulness of the ERG and VEP following vitreoretinal surgery. Methods: Pars plana core vitrectomy (10 mins in duration) was performed using room temperature BSS-Plus infusion in 8 eyes of five Dutch-belted pigmented rabbits. Anesthesia was achieved with isoflurane inhalation. Extradural electrodes placed over the occipital cortex were used for evoked potential recording. Pre-operative and sequential post-operative ERG and VEP (50 computer averaged stimulations at 2 Hz for each test) recordings were made. Results: For the ERG, there was on average a 75% reduction in b-wave amplitude at the end of vitrectomy, and on average a 49% recovery 30 minutes post vitrectomy. Only 2 eyes approached baseline 30 minutes post vitrectomy. For the VEP, there was on average a 47% reduction in amplitude at the end of vitrectomy, and on average an 80% recovery 30 minutes post vitrectomy. Conclusion: The VEP better reveals the responsiveness of the retina in the immediate post vitrectomy state. The ERG, however, is a better test to assess retinal health. Given the potential value of the ERG and VEP as measures of retinal health and implant function, post-operative baseline values would be useful for long-term comparison only if the initial values are obtained after the retina has recovered from its refractory state, which is probably due to infusion of relatively cold fluid during surgery. We have not yet determined the time required to achieve baseline values nor have we determined the impact of surgery on electrically induced cortical potentials, which we are presently studying.
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