动物造模,视网膜色素变性 z-bo 2022-02-06 322

　　Introduction: Retinitis pigmentosa (Rp) is a hereditary degenerative retinal disease, which causes the specific loss of photoreceptors and retinal pigment epithelium (RPE), and is accompanied by severe visual impairment. The use of existing visual pathways to generate visual perception through electrical stimulation of surviving neural components in the retina can restore the vision of these patients. Various locations have been proposed for implantation of stimulation arrays currently under development. These arrays can be placed on the surface of the retina, in the subretinal space in the suprachoroidal space (SCS), in the scleral tissue or on the surface of the sclera. In all methods, the field of view is limited by the surface area of the implanted array. Large electrode array implantation can increase the field of view, but this requires a large scleral incision and related complications. The wide-area retinal electrode array, circular, with a diameter of 10 mm, can be implanted into AgUS II implants through a sclerostomy of similar size, and has been successfully implanted in dogs. Similarly, a 19×8 mm wide-field suprachoroidal electrode array has been successfully implanted in cats. Even with these wide-field electrode arrays, most of the retina is not covered. The implantation of multiple electrode arrays may allow the placement of electrode arrays in all quadrants of the eye, significantly increasing the field of view of implanted retinal prostheses. The purpose of this study is to evaluate the feasibility of multi-electrode array implantation in rabbits.

　　Method: Rabbits are anesthetized by subcutaneous injection of a mixture of ketamine hydrochloride (25 mg/kg) and xylazine hydrochloride (6 mg/kg). 17 Dutch rabbits, weighing 2 to 3 kg, and aged 5 to 6 months. Only the right eye of each animal was used for the study, and the follow-up period was 6 months. Topical application of phenylephrine hydrochloride 2.5% and topikalin 0.5% eye drops to dilate pupils.

　　Test material: An inert custom-made electrode array with a thickness of 15-25 μm, a width of 2 mm and a length of 8 mm is used, connected to a cable of the same width for implantation. The array is made of parylene.

　　Surgery: Open an eyelid, and use a drop of 5% povidone-iodine solution into the fornix to clean the area around the orbit. Establish a scleral incision 2 mm wide and 4 mm behind the limbus. Provide counter-traction by pulling or supporting the limbus, directly opposite the incision. In some cases, the scleral incision has a choroidal bulge that requires anterior chamber puncture to prevent the choroid from breaking with a 30° super sharp blade. Inject GoooLo-GoAK™ into the suprachoroidal space (SCS), immediately under the sclera, and then use blunt conjunctival forceps to advance the array 8-10 mm in the created space. Then cut the redundant array cable about 2 mm from the scleral incision site. Each electrode array is inserted through a separate scleral incision. A fundus examination is then performed to ensure that the array is not placed in the subretinal space or perforated into the vitreous cavity. Then use 6/0vicryl and 8/0nylon sutures to suture the scleral incision site and the surrounding tissues of the conjunctiva. IM injection of buprenorphine of 0.01～0.05 mg/kg was given immediately after the operation for analgesia. Gentamicin was given topically 30 minutes after surgery to reduce the risk of infection.

　　Eye examination: examination includes intraocular pressure (IOP) measurement, examination under an operating microscope, optical coherence tomography (OCT), fundus photography, fluorescein angiography (FA). Before each operation, the rabbits were anesthetized and their pupils dilated as previously described. The baseline examination is carried out before the operation, followed by monthly follow-up examinations until the end of the follow-up. Optical coherence tomography, using a time-domain OCT system, performs 5 mm single-line scanning in the array implant area.

　　Fundus photography and fluorescein angiography: use marginal ear veins to establish venous catheters. Then 0.2 ml of AK-Fluor was injected, and then washed with 1 ml of saline. Immediately after fluorescein injection, a fundus photograph was taken for up to 5 minutes after injection. The assessment includes areas of retinal ischemia, necrosis, or leakage.

　　Result: Clinical examination and auxiliary examination: There was no significant change in intraocular pressure of all animals at baseline and the following 6 months. Eye examination showed that the conjunctival effusion on the conjunctiva was the smallest, lasting for a week, and then gradually decreasing. Fundus examination did not reveal any abnormalities. The implant is easily seen in albino rabbits. The implant was not observed to show any signs of displacement or migration. On the other hand, FA did not find any abnormal vascular leakage or changes in the retinal pigment epithelium. The implant is difficult to detect on the FA image. OCT imaging can show the actual position of the implant in the SCS. Covering the choroid and retina did not show any layer interruption. No array migration from SCS was found on OCT imaging. Compared with the one-month fundus image at six months after the operation, no clinical evidence of lateral or axial displacement of the implanted array was found in the implanted animals.

　　Discussion: Dysfunctional photoreceptor cells are the main sign of retinal degeneration and the main cause of vision loss worldwide. For many years, researchers have been studying ways to restore certain functional vision levels of these blind people. Although the outer retina of RP and age-related macular degeneration (AMD) are reorganized and cells are lost, it seems that neurons in the retina retain the ability to transmit signals. Previous studies have found that the density of ganglion cells in dry AMD is not significantly different from normal eyes, even in areas of the retina where there is almost no remaining photoreceptor. Electrical stimulation of the inner retina has become a well-known method to maintain neuronal activity at a site in the visual pathway, regardless of the potential cause of blindness. This activity propagates along the remaining complete visual pathway to the visual cortex, resulting in some form of visual perception. Although different retinal prosthesis systems share a similar basic architecture, their specific designs are diversified, depending on the placement of the array and the complexity of the implanted electronics. Regardless of the array position, phosphors are a typical response to such electrical stimulation. These phosphors take into account characters and numbers when reaching a certain threshold, and can be used to provide the blind with useful information about the surrounding environment. Among various methods, preretinal and subretinal prostheses have been commercialized. Both pre-retinal and subretinal prostheses enable patients to recognize objects, detect movement, and help their mobility and activities of daily living. Pre-retinal and subretinal prostheses, as well as other experimental methods, provide a limited field of view. Due to the limitations of implanting large electrode arrays, implanting multiple electrode arrays to cover all quadrants of the eye may be a more practical method. Although implanting multiple pre-retinal or subretinal electrode arrays is challenging and may not be practical, the choroidal approach can provide this opportunity. Suprachoroidal implantation has been proven to be a safe implant technique in animal and human studies. The main advantage of the upper choroidal surgical method is the simplicity and safety of the surgical procedure. Although due to the long distance between the electrodes and target cells in the suprachoroidal approach, electrical stimulation may not be as effective and can further limit the resolution of vision. . One option to provide higher resolution central vision and larger field of view is to use a prosthesis with a combined approach. In our research, we implanted multiple arrays in the SCS and showed that it is technically feasible and stable over time. The main difficulties faced by this study are the anatomical variation of the posterior segment of the rabbit and the low sclera stiffness. However, no major complications occurred in any rabbits during the operation. At the beginning of the study, one of our main concerns was the number of arrays and the risk of squeezing or array migration due to SCS disturbances. However, these complications did not occur in our study, which showed that implanting multiple arrays did not increase the risk of migration and compression. Limitations of this study include the small number of animals, the difference in anatomy between rabbits and human eyes, and the use of inactive arrays. However, the main purpose of this study is to test the possibility of implanting multiple arrays in the same subject and the stability of the arrays over time.

　　Conclusion: Our experimental work pointed out the feasibility of implanting multiple electrode arrays in SCS to supplement the visual field of patients with retinal degeneration diseases. This can be a way to improve patient mobility and functionality.