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Epiretinal prostheses are being developed to bypass a degenerated photoreceptor layer and excite surviving ganglion and inner retinal cells. We used custom microfabricated multielectrode arrays with 200-[micro]m-diameter stimulating electrodes and 10-[micro]m-diameter recording electrodes to stimulate and record neural responses in isolated tiger salamander retina. Pharmacological agents were used to isolate direct excitation of ganglion cells from excitation of other inner retinal cells. Strength-duration data suggest that, if amplitude will be used for the coding of brightness or gray level in retinal prostheses, shorter pulses (200 [micro]s) will allow for a smaller region in the area of the electrode to be excited over a larger dynamic range compared with longer pulses (1 ms). Both electrophysiological results and electrostatic finite-element modeling show that electrode-electrode interactions can lead to increased thresholds for sites half way between simultaneously stimulated electrodes (29.4 [+ or -] 6.6 nC) compared with monopolar stimulation (13.3 [+ or -] 1.7 nC, p < 0.02). Presynaptic stimulation of the same ganglion cell with both 200- and 10-[micro]m-diameter electrodes yielded threshold charge densities of 12 [+ or -] 6 and 7.66 [+ or -] 1.30 nC/[cm.sup.2], respectively, while the required charge was 12.5 [+ or -] 6.2 and 19 [+ or -] 3.3 nC. Index Terms--Microelectrodes arrays, retinal electrophysiology, retinal prosthesis.

As microelectrodes gain widespread use for electrochemical sensing, biopotential recording, and neural stimulation, it becomes important to understand the dependence of electrochemical impedance on microelectrode size. It has been shown mathematically that a disc electrode, coplanar in an insulating substrate and exposed to a conducting media, exhibits an inhomogeneous current distribution when a potential step is applied. This distribution is known as the primary distribution, and its derivation also yielded an analytic solution for electrical resistance of the conducting media ([R.sub.s]), between the disc surface and a distant ground, which is inversely proportional to disk radius [[R.sub.s] = 1/(4kr), where h is media conductivity and r is disk radius]. The dependence of spectral impedance on microelectrode radius, however, has not been explored. We verify the analytical solution for resistance using high-frequency (100 kHz) electrochemical impedance data from microelectrodes of varying radius (11-325 [micro]m). For all disc radii, as we approach a lower frequency ([right arrow] 10 Hz), we observe a transition from radial to area dependence (e.g., 1/r [right arrow] 1/[r.sup.2]). We hypothesize that this transition is driven by the fact that the derivation of the primary distribution ignores concentration gradients, but that these gradients cannot be ignored at lower frequencies. Index Terms--Electrochemical sensing, impedance spectroscopy, microelectrode, neural stimulation, primary current distribution.

With applied potential, the current distribution at the surface of a disk electrode is spatially nonuniform and time dependent. This distribution is important to control in applications that desire a uniform current density profile or minimal corrosion. We examine the current density profile of a capacitive disk electrode subjected to a voltage-step using finite element analysis software to solve the system of partial differential equations. In detailed analyses we show quantitatively that the current density shifts from peripheral enhancement to near-uniformity following 1/2 of the lumped element time constant. As charging continues, the current density is slightly enhanced in the central region. We present curves for the evolution of local 'time constants' as time progresses and calculate their effective values. The model is intended to be the basis of future work to control the corrosion profile of biologically implantable electrodes of arbitrary shape. Data suggest a means to control corrosion by retarding the edges of a stimulus pulse. Additionally, smaller electrodes may be more effective in fully utilizing surface area for charge transfer due to their shorter time constants. Index Terms--Current density, double layer, electrochemical processes, implantable electrodes, microelectrodes.

This paper proposes a hybrid algorithm based on artificial immune systems and ant colony optimization for distribution system reconfiguration, which is formulated as a multi-objective optimization problem. The algorithm maintains a population of candidate solutions called antibodies. The search space is explored by means of the hypermutation operator that perturbs existing antibodies to produce new ones. A table of pheromones is used to reinforce better edges during hypermutation. An added innovation is the use of the pheromones to obtain quick solutions to restore the distribution system under contingency situations. The hybrid approach has been successfully implemented on two test networks. The results obtained demonstrate the efficacy of the algorithm. Index Terms--Ant colony optimization, artificial immune system, distribution system reconfiguration, Pareto optimality, power system restoration.

Introduction: As the “Science of Medicine” is getting advanced day-by-day, need for better pedagogies & learning techniques are imperative. Problem Based Learning (PBL) is an effective way of delivering medical education in a coherent, integrated & focused manner. It has several advantages over conventional and age-old teaching methods of routine. It is based on principles of adult learning theory, including student’s motivation, encouragement to set goals, think critically about decision making in day-to-day operations. Above all these, it stimulates challenge acceptance and learning curiosity among students and creates pragmatic educational program. Aim and objectives: To measure the effectiveness of the “Problem Based Learning” as compared to conventional theory/ didactic lectures based learning. Material and Methods: The study was conducted on 72 medical students from Dayanand Medical College & Hospital, Ludhiana. Two modules of problem based sessions designed and delivered. Pre & Post-test score’s scientific statistical analysis was done. Student feed-back received based on questionnaire in the five-point Likert scale format. Results: Significant improvement in overall performance observed. Feedback revealed majority agreement that “Problem-based learning” helped them create interest (88.8 %), better understanding (86%) & promotes self-directed subject learning (91.6 %). Substantial improvement in the post-test scores clearly reveals acceptance of PBL over conventional learning. Conclusion: PBL ensures better practical learning, ability to create interest, subject understanding. It is a modern-day educational strategy, an effective tool to objectively improve the knowledge acquisition in Medical Teaching.

PURPOSE: Reports of morning glory disc anomaly (MGDA) in India have mostly been case reports. The aim of this study was to describe the demographic and clinical profile of patients with MGDA in South India. MATERIALS AND METHODS: A retrospective review of the medical records of patients with MGDA seen at a tertiary eye hospital in South India over a period of 8 years was carried out. The patients' demographic and clinical data were extracted from the case files and were entered into Epi Info reporting software version 7.2.3.0 and then analyzed. RESULTS: There were 51 eyes of 44 patients with MGDA comprised 25 (56.8%) males and 19 (43.2%) females. Seven (15.9%) patients had bilateral MGDA. The mean age for females was 5.8 years (standard deviation [SD]: 5.8) and for males, 11.2 years (SD: 12.1). This difference was not statistically significant with a P = 0.07. The most common ocular associations were strabismus, refractive error, and retinal detachment, whereas the most common systemic associations were cleft lip and cleft palate. Fifty-one percent of eyes were blind at presentation. CONCLUSION: Patients with MGDA in India tend to present late with poor visual prognosis. Early diagnosis and prompt treatment of blinding complications are crucial in reducing the risk of irreversible visual loss. Associated systemic abnormalities highlight the importance of a multidisciplinary approach in the management of patients with this condition. [ABSTRACT FROM AUTHOR]

Objective: To find out whether there exists a correlation between the quantum of energy used and the amount of rise of intraocular pressure (IOP) following neodymium: yttrium aluminum garnet (Nd: YAG) laser capsulotomy. Materials and Methods: A total of 110 patients who had undergone Nd: YAG laser posterior capsulotomy for the management of posterior capsule opacification with a minimum of 3 months following cataract surgery were enrolled after taking written informed consent. After detailed history and ocular examination, Nd: YAG laser capsulotomy was performed. Prelaser IOP was noted. Nd: YAG laser posterior capsulotomy was performed. Laser energy used was noted following which postlaser IOP was also recorded after 1, 2, and 4 h postprocedure. Paired t-test was used for the comparison of means of IOP and energy levels. Receiver operating characteristic analysis was used to predict the cut-off value of energy on the basis of change of IOP from baseline. Results: The mean energy used in the Nd: YAG laser posterior capsulotomy procedure for all patients was 58.57 ± 34.63 mJ. The mean IOP at 1st h follow-up was 15.32 ± 2.91 mmHg, at 2nd h follow-up was 16.24 ± 3.23 mmHg, and at 4th h follow-up was 16.18 ± 3.35 mmHg. At all three follow-ups, the mean change in IOP was found to be statistically significant (P < 0.001). Conclusion: Postlaser IOP rise is minimal and transient; it varies with the amount of energy used. [ABSTRACT FROM AUTHOR]