There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

비만아 부모의 돌봄 경험: q 방법론

Simulations of artificial vision suggest that 1000 electrodes may be required to restore vision to individuals with diseases of the outer retina. In order to achieve such an implant, new technology is needed, since the state-of-the-art implantable neural stimulator has at most 22 contacts with neural tissue. A critical component of this system is the multi-channel, stimulating electrode array. This array must meet very challenging, competing requirements for manufacturing, integration, surgical handling, and biocompatibility. Our lab has evaluated 3 polymers as retinal prosthesis substrates: polyimide, parylene, and silicone.

A comparison of retinal prosthesis electrode array substrate materials

An Intraocular Camera for Retinal Prostheses: Restoring Sight to the Blind

Subjects with retinal degeneration have been implanted with a 60+ electrode prosthesis in an FDA-approved clinical trial. The subjects had bare light perception or worse due to Retinitis Pigmentosa. They were evaluated using a number of tests such as grating visual acuity, object and letter recognition and orientation/ mobility. As of March 2010, over 30 subjects have been implanted with excellent safety. Subjects have been implanted an average of 18 months (range 6.7-33) and are tested with the Argus II system turned ON vs. OFF. All subjects now perceive light and can complete tasks significantly better (p< 0.05) with the system ON vs. OFF. Five subjects have regained measurable visual acuity (2.9 logMAR) with the system ON. Of 24 implanted subjects, 95% were able to correctly identify test letters with the system ON compared to 8% with the system OFF. With up to 3.2 total years of follow-up on the 32 subjects, this now constitutes the largest study of a visual prosthesis to date. The results confirm previous reports using the Argus I device as to the ability of this system to restore functional vision over the long-term. Higher resolution devices are in development. For more information, please contact Cathy Naples at (216) 707-6490. Mark S. Humayun, MD, PhD

Interim Performance Results from the Second Sight® ArgusTM II Retinal Prosthesis Study

End-stage age-related macular degeneration (AMD) and retinitis pigmentosa (RP) are two major retinal degenerative (RD) conditions that result in irreversible vision loss. Permanent eye damage can also occur in battlefields or due to accidents. This suggests there is an unmet need for developing effective strategies for treating permanent retinal damages. In previous studies, co-grafted sheets of fetal retina with its retinal pigment epithelium (RPE) have demonstrated vision improvement in rat retinal disease models and in patients, but this has not yet been attempted with stem-cell derived tissue. Here we demonstrate a cellular therapy for irreversible retinal eye injuries using a "total retina patch" consisting of retinal photoreceptor progenitor sheets and healthy RPE cells on an artificial Bruch's membrane (BM). For this, retina organoids (ROs) (cultured in suspension) and polarized RPE sheets (cultured on an ultrathin parylene substrate) were made into a co-graft using bio-adhesives [gelatin, growth factor-reduced matrigel, and medium viscosity (MVG) alginate]. In vivo transplantation experiments were conducted in immunodeficient Royal College of Surgeons (RCS) rats at advanced stages of retinal degeneration. Structural reconstruction of the severely damaged retina was observed based on histological assessments and optical coherence tomography (OCT) imaging. Visual functional assessments were conducted by optokinetic behavioral testing and superior colliculus electrophysiology. Long-term survival of the co-graft in the rat subretinal space and improvement in visual function were observed. Immunohistochemistry showed that co-grafts grew, generated new photoreceptors and developed neuronal processes that were integrated into the host retina. This novel approach can be considered as a new therapy for complete replacement of a degenerated retina.

/pdf/co-grafts-of-human-embryonic-stem-cell-derived-retina-3q7uopkr28.pdf

Co-grafts of Human Embryonic Stem Cell Derived Retina Organoids and Retinal Pigment Epithelium for Retinal Reconstruction in Immunodeficient Retinal Degenerate Royal College of Surgeons Rats.

Apparatus, systems, and devices are described that utilize an adjustable biological tissue cutting handpiece that is based on selectable settings. The biological tissue cutting handpiece includes a cutter tip that allows multiple duty cycles as well as multiple port configurations. For example, when working next to the retina, the port could be adjusted to be a smaller size, allowing delicate membrane dissection. When working near or in less sensitive tissue, e.g. the center of the eye, the port could be wide open. The port aperture size can be independent of cut speed, allowing a surgeon to work at high speed both next to the retina and away from the retina. High speeds have been shown to have increased tissue (e.g., vitreous) removal, e.g., in 25 and 23-gauge instruments. Duty cycle is not necessarily dependent on cut speed, allowing high cutter performance and varied flow characteristics.

Mark S. Humayun

Papers

A comparison of retinal prosthesis electrode array substrate materials

An Intraocular Camera for Retinal Prostheses: Restoring Sight to the Blind

Interim Performance Results from the Second Sight® ArgusTM II Retinal Prosthesis Study

Co-grafts of Human Embryonic Stem Cell Derived Retina Organoids and Retinal Pigment Epithelium for Retinal Reconstruction in Immunodeficient Retinal Degenerate Royal College of Surgeons Rats.

Selectable stroke cutter