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

Purpose : Diabetic retinopathy (DR) is a leading complication of diabetes. It is thought that increased rod metabolism under dark adaptation exacerbates hypoxia in diabetic retina. Nowadays most treatments for DR are invasive and need multiple clinic visits. Recently a phototherapeutic contact lens has been designed to provide illumination to retina as a means to supress dark adaptation. It may be possible to delay the progression of DR. The purpose of this study is to explore the bioactivity and safety of this device.
Methods : Six eyes from three healthy mature white New Zealand rabbits were used. The phototherapeutic contact lens was placed on treated eye. An non-phototherapeutic contact lens was used on the fellow eye as a control. To determine bioactivity of photoreceptors, an ERG was performed. Flash response, including amplitude and implicit time on scotopic condition were analyzed at different flash intensities (100, 300, 1000, 3000, 10000, 25000 mcd.s/m^2, respectively). Animals were under a 20-minutes period of dark adaption before any ERG. Then the contact lens were swapped on the eyes and the ERG were repeated. The whole process was performed in a dark room under dim red light. Once ERG were completed, the phototherapeutic contac lens was sutured to the eye for a long–term period (28 days) to verify safety. There will be a statistical analysis using Graph Pad Prism 7.0, determining the degree of correlation between the groups. Histological analysis will be performed to determine safety.
Results : The ERG showed that both the amplitude and implicit time of b-wave in the treated eye were significantly shorter than the untreated eye under scotopic conditions (Figure 1). No significant difference in the amplitude and implicit time of a-wave was observed. A representative plot (Figure 2) shows significant depression of b-wave, both in the amplitude and implicit time (amplitude: p=0.01; implicit time: p<0.001).
Conclusions : The phototherapeutic contact lens can effectively reduce the bioactivity of the retina, without ocular side effects in an acute follow-up. Further studies should be performed for a long-term placement in both healthy and retinal ischemic animal models to determine whether this device can reduce oxygen consumption in retina and delay disease progression. Long-term histology from contact lens safety is on going and will be presented.

Effectiveness and Safety of a phototherapeutic contact lens for Diabetic Retinopathy

The present invention is a flexible circuit electrode array for improved layer adhesions where the metal conductors overlap the polymer insulator. The steps to build the flexible circuit are as follows. Deposit a base polymer layer. Deposit a conductive trace over the base polymer layer. Deposit a top polymer layer over the trace and prepare a void in the top polymer layer smaller than the surface of the trace. Deposit an electrode on the trace through the void with a periphery larger than, and overlapping the void.

Flexible circuit electrode array for improved layer adhesion

The visual prosthesis being developed will provide useful vision to people blind because of photoreceptor loss due to retinal degenerative diseases such as age related macular degeneration (AMD) and retinitis pigmentosa (RP). A retinal prosthesis will replace photoreceptor function with an electronic device. In a healthy retina the pho- toreceptors initiate a neural signal in response to light. Photoreceptors are almost com- pletely absent in the retina of end-stage RP patients and in the macular region of AMD patients. However, cells to which photoreceptors normally synapse, (i.e. bipolar cells) survive at high rates. In blind volunteers, we have shown that controlled electrical signals applied with a microelectrode positioned near the retina elicit the perception of a spot of light that correlates both spatially and temporally to the applied stimulus.1,2 When multiple electrodes are activated in a two dimensional electrode array, a number of small spots of light are perceived by the patient(s) which when viewed together form an image representative of the pattern of active electrodes. Thus similar to how an image is formed by a dot-matrix printer, when controlled pattern electrical stimulation of the remaining retinal neurons is coupled with an extraocular image acquisition and transmission system, it could allow blind patients to regain form vision.

Electrical Stimulation of the Human Retina

Currently, blindness cannot be cured and patients’ living quality can be compromised severely. Ultrasonic (US) neuromodulation is a promising technology for the development of noninvasive cortical visual prosthesis. We investigated the feasibility of transcranial focused ultrasound (tFUS) for noninvasive stimulation of the visual cortex (VC) to develop improved visual prosthesis. tFUS was used to successfully evoke neural activities in the VC of both normal and retinal degenerate (RD) blind rats. Our results showed that blind rats showed more robust responses to ultrasound stimulation when compared with normal rats. ( ${p} , two-sample t-test). Three different types of ultrasound waveforms were used in the three experimental groups. Different types of cortical activities were observed when different US waveforms were used. In all rats, when stimulated with continuous ultrasound waves, only short-duration responses were observed at “US on and off” time points. In comparison, pulsed waves (PWs) evoked longer low-frequency responses. Testing different parameters of PWs showed that a pulse repetition frequency higher than 100 Hz is required to obtain the low-frequency responses. Based on the observed cortical activities, we inferred that acoustic radiation force (ARF) is the predominant physical mechanism of ultrasound neuromodulation.

Transcranial Focused Ultrasound for Noninvasive Neuromodulation of the Visual Cortex

For the first time, a paradigm shift in the treatment of retinal ischemia is proposed: providing localized supplemental oxygen to the ischemic tissue via an implanted MEMS device. A passive MEMS oxygen transporter is designed, built and tested in both artificial eye models and porcine cadaver eyes to confirm various hypotheses. The finite element modeling results predict that the proposed approach can treat complete retinal ischemia.

Mark S. Humayun

Papers

Effectiveness and Safety of a phototherapeutic contact lens for Diabetic Retinopathy

Flexible circuit electrode array for improved layer adhesion

Electrical Stimulation of the Human Retina

Transcranial Focused Ultrasound for Noninvasive Neuromodulation of the Visual Cortex

MEMS oxygen transporter to treat retinal ischemia