PURPOSE:Measure outflow resistance of the styrene-block-isobutylene-block-styrene (SIBS) microshunt when sutures of differing lengths, sizes, and materials partially occlude the lumen. DESIGN:In vitro experiment METHODS: The SIBS microshunt proximal end was connected to a gravity perfusion system. The distal tip was submerged within a fluid-filled covered collection-beaker. Microshunt flow was quantified through collection-beaker mass changes. Each 5-minute trial was replicated 4 times per condition. Various sutures were inserted into the distal end of the microshunt's lumen, and outflow resistance was measured in partly occluded states (4-mm or 8-mm suture length inserted, 9-0 or 10-0 suture diameters, Vicryl or nylon suture). The 4-mm 10-0 nylon condition was repeated with sutures from different lots to investigate the effects of suture manufacturing variability. MAIN OUTCOME MEASURE:Outflow resistance. RESULTS:Resistance of nonoccluded SIBS microshunts (n = 5) was 1.74 ± 0.06 mmHg/μl/minute, matching the theoretical 1.76 mmHg/μl/minute from the Hagen-Poiseuille formula. Partial occlusion with a 4-mm 10-0 suture increased resistance to 3.42 ± 0.13 mmHg/μl/minute for nylon and 3.55 ± 0.13 for Vicryl. Partial occlusion with an 8-mm 10-0 suture increased resistance to 4.66 ± 0.21 for nylon and 5.08 ± 0.23 for Vicryl. Partial occlusion with a 4-mm 9-0 suture increased resistance to 5.11 ± 0.28 for nylon and 5.00 ± 0.27 for Vicryl. Partial occlusion with an 8-mm 9-0 suture increased resistance to 7.24 ± 0.37 for nylon and 7.87 ± 0.55 for Vicryl. Resistance differed significantly between nonoccluded versus all partially occluded states (P < 0.0001), 4- versus 8-mm partially occlusion lengths (P < 0.0001), 10-0 versus 9-0 suture diameters (P < 0.0001), and 4-mm 10-0 nylon sutures from different lots (P < 0.0001). No difference was observed between suture materials (P > 0.05) or different microshunts (P > 0.05). CONCLUSIONS:Nonoccluded microshunt resistance measured by the perfusion model matched theoretical values. Partial occlusion with either suture material caused substantial resistance increases, depending on suture diameter and length, compared with nonoccluded microshunts. If desired, partial occlusion with 4-mm 9-0 nylon or 8-mm 10-0 nylon suture is recommended, producing resistance consistently above the hypotony threshold while maintaining optimal therapeutic efficacy. FINANCIAL DISCLOSURE(S):Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

PURPOSE:To compare 12-month effectiveness and safety of 63-μm gelatin microstent (Xen63) versus 45-μm gelatin microstent (Xen45). DESIGN:Multicenter, retrospective cohort study. SUBJECTS:Two hundred eyes of 200 patients (100 in each Xen63 and Xen45 group), with or without phacoemulsification. METHODS:Consecutive patients undergoing 63-μm microstent implantation across 4 countries (Canada, Italy, Austria, and Belgium) were compared with matched controls who underwent 45-μm microstent implantation. MAIN OUTCOME MEASURES:Primary outcome measure was the probability of complete success at 1 year: (1) no 2 consecutive intraocular pressure (IOP) >14 or < 6 mmHg with 2 lines of vision loss and (2) ≥20% reduction from decision IOP, without glaucoma medications or reoperations. Qualified success allowed glaucoma medications and laser trabeculoplasty. Secondary outcomes included success with upper IOP cutoffs of 17 and 21 mmHg, postoperative IOP and medications course, complications, interventions, and reoperations. RESULTS:Complete success favored 63-μm microstent (56.9% vs. 43.9%, P = 0.017), using IOP cutoff of 14 mmHg. The 45-μm microstent was associated with an increased hazard of failure compared with the 63-μm microstent (hazard ratio, 1.9; 95% confidence interval, 1.2-3.0). Complete success using IOP cutoffs of 17 and 21 mmHg in the 63- versus 45-μm group was 60.1% versus 53.9% (P = 0.156) and 60.1% versus 55.0% (P = 0.243), respectively. Qualified success was not significantly different between the 2 groups using any IOP threshold (P > 0.05). At 12 months, the 63-μm group had significantly lower IOP (mean, 14.6 ± 7.6 vs. 15.8 ± 6.1 mmHg; P = 0.021) and medication count (0.6 ± 1.1 vs. 1.1 ± 1.5; P = 0.024). Postoperative needling was performed in 16.0% and 18.0% of 63- and 45-μm microstent-implanted eyes, respectively. Incidence of early postoperative choroidal effusion was higher in the 63-μm group (25.0% vs. 6.0%; P < 0.001). Interventions (62.0% vs. 59.0%) and reoperations (21.0% vs. 15.0%) were comparable between the groups (P > 0.050). CONCLUSIONS:Xen63 demonstrated superior IOP-lowering effectiveness compared with its 45-μm variant in patients requiring more robust IOP targets. Xen63-implanted eyes experienced a higher incidence of early postoperative choroidal effusion, the majority of which were transient. FINANCIAL DISCLOSURE(S):Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Mitomycin C is an alkylating agent with the ability to suppress fibroblast proliferation and activity, making it a powerful antifibrotic. It has therefore become popular in glaucoma filtering surgeries, used both intraoperatively during bleb formation and postoperatively as an adjunct to bleb needling. This report presents a rare but serious risk of bleb needling with Mitomycin C at the slit lamp, where inadvertent movement of the patient resulted in an orbital injection. The patient quickly developed focal tissue inflammation and necrosis, presenting one day after the procedure with complete ptosis, ophthalmoplegia, and a palpable orbital mass. After appropriate imaging and an excisional biopsy to exclude infectious, infiltrative, and neoplastic causes, this was managed with close observation and continued improvement, and resolution of most orbital sequelae.

Objective To compare sex and medical school graduate type differences in cataract surgical training volumes at Canada's largest residency program, the University of Toronto (UoT). Design Retrospective cohort study Participants Ophthalmology residents completing cataract surgical training from 2015 to 2020. Methods Data collected from surgical logbooks at the main cataract surgical teaching site at UoT were analyzed from July 1, 2015, to June 30, 2020. Data collected included stage of resident training and degree of participation for each case. The main outcome measure was mean number of complete cataract cases as a function of resident sex, medical school graduate type, and level of training. Results Thirty-five (19, 54.3% female) residents completed cataract surgical training during the study period. There were 24 (68.6%) Canadian medical graduates (CMGs) and 11 (31.4%) international medical graduates (IMGs). Female residents performed a lower mean number of complete cataract cases compared to males (464.2 versus 504.8, respectively). IMGs completed on average 110.0 (22.8%) fewer cataract cases compared to CMGs. Compared to all residents, female IMGs had the lowest number of complete cataract cases (mean of 380.8 versus 465.7, respectively). The greatest difference occurred between male CMGs and female IMGs, with male CMGs performing 153.8 (40.4%) more complete cases (534.6 vs 380.8, respectively). Conclusion The greatest difference in surgical volumes occurred between CMGs and IMGs. Female IMGs had the lowest complete cataract case volumes compared to all residents. Our study highlights novel medical school graduate type disparities in cataract surgical training warranting further exploration.

The expansion of medical knowledge confronts learners with information overload. As such, it is advantageous to explore methods to efficiently teach and keep learners engaged.1Cutrer W Spickard III, W Triola M et al.Exploiting the power of information in medical education.Med Teach. 2021; 43: 517-524Google Scholar Strategies that integrate teaching with prior knowledge are one of the top 10 factors that positively influence learning.2Hattie J. 250+ Influences on student achievement [Internet]. Visible Learning Limited Partnership and Cognition Education Group, 2017. Available at: https://visible-learning.org/wp-content/uploads/2018/03/VLPLUS-252-Influences-Hattie-ranking-DEC-2017.pdf (accessed 13 July 2022).Google Scholar Advance organizers (AOs) are educational tools that help learners link and structure new information with prior knowledge.3Ing E Tyndel F. Award-winning medical teaching. EBI Publishing, Toronto2022Google Scholar4Ausubel D. The use of advance organizers in the learning and retention of meaningful verbal material.J Educ Psychol. 1960; 51: 267Crossref Scopus (725) Google Scholar In this learner satisfaction survey, we examine the utility of AOs in oculoplastic surgery teaching. Because ice hockey is the most popular sport in Canada, hockey-related AOs were incorporated into an introductory 3-hour lecture on oculoplastics (see Table 1).Table 1Examples of hockey advance organizers used during lectureTeaching objectiveOculoplastics detailsHockey advance organizerTeam building and camaraderieIntroductory slide: “Oculoplastics Hockey School”A group photographs of the students taken at their welcoming party was edited to have each resident have a Team Canada Hockey jersey. In the team graphic, in place of hockey sticks, a hockey scalpel blade was used.Introduction to topicThe components of oculofacial plastic surgery (oculoplastics)Oculoplastics is likened to the hat trick of eyelid, lacrimal, and orbital diseases. The inclusion of cosmetics and oculofacial surgery is a Texas hat trick or pants trick.Eyelid anatomyTarsus of the eyelidThe tarsus was compared to the protective hockey pads worn by players.Eyelid anatomyGrey line and lash aberrancyA hockey stick scalpel blade was used to split the lid at the grey line. The importance of identifying the grey line was compared with the blue line on a hockey rink and the consequences of lash aberrancy with the penalty of being “offside.”Eyelid anatomy and equity, diversity, and inclusionThe anatomic difference between Asian and Western eyelid anatomyLarry Kwong, a Chinese hockey player with low lid folds, was shown. Larry Kwong broke the National Hockey League colour barrier in 1948. See Figure 1.Introduction to the nasolacrimal systemEpiphoraThe nasolacrimal system and tearing were introduced by showing a graphic of Toronto hockey fans crying over the 54-year Stanley Cup drought.Trauma and preventionOrbital fracturesA picture of the Mona Lisa with a hockey helmet and cage was shown. It was stated, “To keep your Mona Lisa looks, prevention is the best treatment.”Orbital traumaMechanisms of orbital fractureHockey pucks striking the orbital rim versus the globe were used to illustrate the buckling versus hydraulic theories.Orbital tumoursOrbital lymphoma with salmon patch lesion and infiltrative mass on the scanThe National Hockey League has the same initials as non-Hodgkins lymphoma (NHL) and reminded learners that orbital lymphoma is usually the non-Hodgkins’ variant.Diagnostic prediction modelsRisk stratification of patients undergoing temporal artery biopsyAn online betting commercial with a famous hockey star was shown. Instead of gambling, learners are suggested to choose wisely using a diagnostic prediction model for giant cell arteritis.A culture of learning from mistakesOrbital diagnosis. A table of the most common causes of proptosis and orbital tumours was shown.It was emphasized that orbital diseases may not follow the expected pattern, but as long as we learn from our mistakes, we can still achieve “greatness.” The clothes dryer from Sidney Crosby's childhood was shown with dents and puck marks. Crosby used to practice hockey in the basement, and his errant shots hit the dryer.Climate changeSkin cancer, trachoma, Bell's palsy (Lyme disease)A graphic of a hockey player contemplating a future of thin ice and an approximation of Michael Mann's controversial “hockey stick” climate change graph are shown to discuss climate change.Land acknowledgementNot applicableA hockey jersey of the Indigenous peoples of Tkaronto was used as a graphic.Break time between lecturesNot applicableA picture of a Zamboni during intermission was used during the lecture break at halftime.GCA, giant cell arteritis. Open table in a new tab GCA, giant cell arteritis. This study was approved by the Michael Garron Hospital Research Ethics Board and compliant with the Declaration of Helsinki. The study population consisted of 42 beginning ophthalmology residents who attended the Canada-wide “Introduction to Ophthalmology Course” in June 2022 at the University of Toronto. The in-person “Introduction to Oculoplastics” lecture began by describing what ice hockey was, explaining that ice hockey was Canada's predominant official sport, and comparing ice hockey to field hockey. It was disclosed that hockey analogies would be used as AOs during the lecture to introduce or scaffold the oculoplastics information and as a segue to topics including climate change and equity, diversity, and inclusion (Fig. 1). Immediately after the lecture, the residents rated their perceived utility of the AOs for learning using a visual analogue scale anchored at 0 (strongly disagree) and 10 (strongly agree), with 5 being neutral. The response rate for the voluntary survey was 37 of 42 residents (88%), who were, on average, 29 years of age, with 20 of 36 (56%) male. Thirty-two of the learners (87%) were from Canada, and 5 (13%) were from the Caribbean. Twelve learners (32%) did not play or watch ice hockey or field hockey. Twenty-two students (60%) felt that the AOs helped their learning, 9 (24%) were neutral, and 6 (16%) did not find the AOs helpful for their learning. The survey margin of error was 5.6%. The average rating of the AOs for learning was 6.5/10 ± 2.3. On multivariable linear regression with an adjusted R2 of 0.242, there was no heteroskedasticity, no omitted variable bias, and no multicollinearity. There was no statistically significant association between the rating of the AOs and age (p = 0.088), gender (p = 0.992), familiarity with ice hockey (p = 0.410), or Canadian residence (p = 0.169). Familiarity with field hockey was positively associated with a higher AO rating (p = 0.005). AOs can enhance student motivation and student engagement and improve comprehension,3Ing E Tyndel F. Award-winning medical teaching. EBI Publishing, Toronto2022Google Scholar which was supported by the majority of survey comments. Because AOs may incorporate diverse spheres of information, they may promote innovative thinking and may teach learners to develop scaffolding techniques for their future adaptive learning. AOs are disadvantageous if they cause information overload because learners cannot use them to bridge information gaps. In 2022, the residents (n = 31) graded the oculoplastics lecture at 4.65/5. In 2021, a different group of residents (n = 27) evaluated the same introductory oculoplastics lecture delivered by the same speaker (E.I.) with similar slides but no hockey-related AOs at 4.24/5. AOs may have contributed to an 8% improvement in the lecture evaluation, but comparing the lecture scores from different years is not wholly accurate because a different group of residents was involved. At the time of submission, the average score for all 51 of the 2022 course lectures was unavailable. In 2021, the average lecture score was 4.59/5. In summary, 60% of beginning ophthalmology residents felt that a lecture with hockey-related AOs helped them learn oculoplastics. Although AOs can enhance the subjective appreciation of ophthalmology teaching by learners, AOs with a widespread appeal should be used. We thank Gwyneth Evans from the Museums and Archives of Vernon, BC, for permission to use the photograph of Larry Kwong. The hockey clipart image in Table 1 was from the free clip art site https://clipartix.com/hockey-clipart-image-16604/. We thank Kathy Cao and Sandra Gauci for administrating the Toronto Ophthalmology Resident Introductory Course. The authors have no financial or personal relationships that would bias this work.

Précis: Use of a scleral tunnel technique instead of a patch graft can be considered in most cases of tube shunt implantation. Grafts may still be considered in younger (<65 y old) East Asians. Purpose: (1) To assess the risk factors for tube exposure with a graft-free implantation technique and (2) to examine 5-year outcomes of graft-free tube shunt insertion. Methods: This was a retrospective case series of 204 consecutive eyes undergoing a glaucoma tube shunt implantation with a scleral tunnel technique in lieu of a graft. Preoperative and postoperative best-corrected visual acuity, intraocular pressure, and number of glaucoma medications were compared. Failure was defined as the following: (1) intraocular pressure >21 mm Hg or ≤5 mm Hg on 2 consecutive visits after 3 mo; (2) required additional glaucoma surgery; (3) loss of light perception. Univariable and multivariable regression analyses were conducted to identify risk factors of tube exposures. Results: Intraocular pressure and the number of glaucoma medications were significantly decreased at all postoperative time points ( P <0.001). Success rates were 91% at year 1, 75% at year 3, and 67% at year 5. The most common early (<3 mo) complication was tube malpositioning. The most common late (>3 mo to 5 y) complications were corneal complications and uncontrolled intraocular pressure. By year 5, 6.9% of tubes were exposed. Multivariable regression showed that age less than 65 years old (odds ratio: 3.66, P =0.04) and East Asian ethnicity (odds ratio: 3.36, P =0.04) were associated with significantly increased risk of tube exposure. Conclusions: Graft-free glaucoma tube implantation has comparable long-term outcomes and complication rates to shunts with a graft. Younger (<65 y old) East Asians are at greater risk of tube exposure without a graft.

The Poisson-Nernst-Planck equations with generalized Frumkin-Butler-Volmer boundary conditions (PNP-FBV) describe ion transport with Faradaic reactions and have applications in a wide variety of fields. We solve the PNP-FBV equations using an adaptive time-stepper based on a second-order variable step-size, semi-implicit, backward differentiation formula (VSSBDF2). When the underlying dynamics are such that the solutions converge to a steady-state solution, we observe that the adaptive time-stepper produces solutions that "nearly" converge to the steady state and that, simultaneously, the time-step sizes stabilize to a limiting size dt∞. Linearizing the SBDF2 scheme about the steady state solution, we demonstrate that the linearized scheme is conditionally stable and that this is the cause of the adaptive time-stepper's behavior. Mesh-refinement, as well as a study of the eigenvectors corresponding to the critical eigenvalues, demonstrate that the conditional stability is not due to a time-step restriction caused by high-frequency contributions. We study the stability domain of the linearized scheme and find that its boundary can have corners as well as jump discontinuities.

While the cholesterol biosynthesis pathway has been extensively studied, recent work has forged new links between inhibition of specific sterol pathway enzymes, accumulation of their unique sterol substrates, and biological areas as diverse as cancer, immunology, and neurodegenerative disease. We recently reported that dozens of small molecules enhance formation of oligodendrocytes, a glial cell type lost in multiple sclerosis, by inhibiting CYP51, Sterol 14-reductase, or EBP and inducing cellular accumulation of their 8,9-unsaturated sterol substrates. Several adjacent pathway enzymes also have 8,9-unsaturated sterol substrates but have not yet been evaluated as potential targets for oligodendrocyte formation or in many other biological contexts, in part due to a lack of available small-molecule probes. Here, we show that genetic suppression of SC4MOL or HSD17B7 increases the formation of oligodendrocytes. Additionally, we have identified and optimized multiple potent new series of SC4MOL and HSD17B7 inhibitors and shown that these small molecules enhance oligodendrocyte formation. SC4MOL inhibitor CW4142 induced accumulation of SC4MOL's sterol substrates in mouse brain and represents an in vivo probe of SC4MOL activity. Mechanistically, the cellular accumulation of these 8,9-unsaturated sterols represents a central driver of enhanced oligodendrocyte formation, as exogenous addition of purified SC4MOL and HSD17B7 substrates but not their 8,9-saturated analogs promotes OPC differentiation. Our work validates SC4MOL and HSD17B7 as novel targets for promoting oligodendrocyte formation, underlines a broad role for 8,9-unsaturated sterols as enhancers of oligodendrocyte formation, and establishes the first high-quality small molecules targeting SC4MOL and HSD17B7 as novel tools for probing diverse areas of biology.

Minimally invasive glaucoma surgeries (MIGS) offer an effective way to lower intraocular pressure without inducing extensive trauma to the anterior segment. In order to predict their efficacy, an analytical model of the conventional aqueous humor outflow pathway is developed using a resistor network. The model describes outflow through the normal eye and allows for the effects of geometric changes in the outflow pathway as IOP changes. By selectively removing these resistors, the model can be used to examine and predict the outcomes of several surgical procedures currently used to treat glaucoma. Treatments examined include traditional trabeculectomy, several ab interno methods for trabeculotomy and trabeculectomy, as well as recently developed trabecular stents that bypass the trabecular meshwork and dilate Schlemm canal. The model's predictions for the efficacy of these procedures generally matched well with the efficacy determined in experimental studies, although it tended to somewhat overestimate the efficacy of these procedures. Matching the model to experimental data indicated that a partial trabeculotomy substantially increases flow to collector channels within that region and approximately 1.5 clock hours past the ends of the trabeculotomized region. Similarly, trabecular bypass stents substantially increase flow to collector channels up to 1.5 clock hours past the open ends of the stent. The resistor model we have developed can be used to predict the efficacy of a variety of MIGS procedures. Circumferential flow in Schlemm canal extends the efficacy of MIGS, but this effect is limited to a few clock hours.

The Poisson-Nernst-Planck equations with generalized Frumkin-Butler-Volmer boundary conditions (PNP-FBV) describe ion transport with Faradaic reactions, and have applications in a number of fields. In this article, we develop an adaptive time-stepping scheme for the solution of the PNP-FBV system based on two time-stepping methods: a fully-implicit (VSBDF2) method, and a semi-implicit (VSSBDF2) method. We present simulations under both current and voltage boundary conditions and demonstrate the ability to simulate a large range of parameters, including any value of the singular perturbation parameter ϵ. Many electrochemical systems of interest are subject to sudden changes in forcing separated by periods with constant or no forcing. The adaptive time-stepper easily addresses such time-scale changes. When the underlying dynamics is one that would have the solutions converge to a steady-state solution, we observe that the adaptive time-stepper based on the VSSBDF2 method produces solutions that “nearly” converge to the steady-state solution and that, simultaneously, the time-step sizes stabilize to a limiting size dt∞. While the adaptive time-stepper based on the fully-implicit (VSBDF2) method is not subject to such time-step stability restrictions, the required nonlinear solve incurs additional computational cost. We profile both methods to identify regimes of the perturbation parameter ϵ where one method is favourable over the other. The Matlab code used in this work can be found at https://github.com/daveboat/vssimex_pnp.

The Xen Gel Stent lowers intraocular pressure by shunting aqueous humor to the subconjunctival space. While published studies include both open conjunctiva and closed conjunctiva approaches, most publications feature a closed conjunctiva, ab interno approach. While this approach is widely used, other approaches may be preferred for some patients. This paper provides details on surgical steps and tips for enhancing outcomes for an open conjunctiva technique for the implantation of the Xen Gel Stent, as well as reasoning as to when this approach should be used.

PURPOSE:Orbital cellulitis is a rare complication of aqueous tube shunt surgery. Nine cases have been described in the literature, though the microbiologic etiology is rarely reported. Management with intravenous antibiotics and/or explantation has been described.METHODS:This is a case report and literature review.CASE:A 64-year-old woman developed pain, periorbital swelling, limited extraocular motility, proptosis, and conjunctival injection 3 days following implantation of an Ahmed Glaucoma Valve. Computed tomography of the orbits with contrast showed soft tissue fat stranding consistent with orbital inflammation. Initial medical management with topical and intravenous ceftriaxone and vancomycin was unsuccessful. Surgical removal of the implant was performed and intraoperative cultures demonstrated florid Pseudomonas aeruginosa growth. Antibiotic coverage was changed to Piperacillin-Tazobactam for 3 days, with eventual resolution of her orbital symptoms.CONCLUSIONS:We report the first case of orbital cellulitis after implantation of a glaucoma device associated with P. aeruginosa. Failure of intravenous and topical antibiotics led to explantation of the valve and targeted intravenous antibiotic therapy with subsequent clinical improvement.

Purpose: To compare the intraoperative complication rates in cataract surgery performed by resident trainees and staff ophthalmologists. Setting: Kensington Eye Institute, University of Toronto, Toronto, Canada. Design: Prospective case series. Methods: This study included 8738 consecutive cases of primary phacoemulsification cataract surgery performed by staff surgeons and resident trainees from January to December 2016. There were no exclusion criteria. Data collected included the level of resident training, case complexity, degree of resident involvement, and intraoperative complications. Primary outcome measures included intraoperative complication rates and level of complexity of cataract surgeries performed by resident trainees and staff surgeons. Results: Resident trainees were involved in 44% of surgeries. Of those, 82% were completed in their entirety by a resident and 18% were performed by both the staff surgeon and resident. Staff surgeons performed 56% of all surgeries without resident involvement. Sixty-seven percent of surgeries were simple and 33% were complex, with small pupil or intraoperative floppy-iris syndrome being the most common reason for complex cases. For simple cases, there was no difference in the overall complication rates (1.7% and 2.0%; P = .52), posterior capsule rupture rates (0.9% and 0.8%; P = .76), or vitreous loss rates (0.4% and 0.2%; P = .08) between staff and residents, respectively. Conclusion: There were no differences in complication rates between the two groups. (C) 2018 ASCRS and ESCRS

The Poisson-Nernst-Planck equations with generalized Frumkin-Butler-Volmer boundary conditions (PNP-FBV) describe ion transport with Faradaic reactions and have applications in a wide variety of fields. In this article, we develop a variable step size implicit-explicit time stepping scheme for the solution of the PNP-FBV equations. We test our numerical scheme on a simplified toy version of the PNP-FBV equations, paying special care to the treatment of the coupled nonlinear terms in the boundary condition. We evaluate various ways of incorporating the boundary condition into the scheme and a method based on ghost points is chosen for its favorable numerical properties compared to the alternatives. In fact, we observe that when the underlying dynamics is one that would have the solutions converge to a steady state solution, the numerical simulation does not result in the time-step sizes growing larger along with the expected convergence. We observe that the time-step sizes threshold at a particular step size. By performing an A-stability analysis we demonstrate that this thresholding does not appear to be due to a stability constraint. Using the developed numerical method, we are able to run simulations with a large range of parameters, including any value of the singular perturbation parameter epsilon.

Linear sweep and cyclic voltammetry techniques are important tools for electrochemists and have a variety of applications in engineering. Voltammetry has classically been treated with the Randles-Sevcik equation, which assumes an electroneutral supported electrolyte. In this paper, we provide a comprehensive mathematical theory of voltammetry in electrochemical cells with unsupported electrolytes and for other situations where diffuse charge effects play a role, and present analytical and simulated solutions of the time-dependent Poisson-Nernst-Planck equations with generalized Frumkin-Butler-Volmer boundary conditions for a 1:1 electrolyte and a simple reaction. Using these solutions, we construct theoretical and simulated current-voltage curves for liquid and solid thin films, membranes with fixed background charge, and cells with blocking electrodes. The full range of dimensionless parameters is considered, including the dimensionless Debye screening length (scaled to the electrode separation), Damkohler number (ratio of characteristic diffusion and reaction times), and dimensionless sweep rate (scaled to the thermal voltage per diffusion time). The analysis focuses on the coupling of Faradaic reactions and diffuse charge dynamics, although capacitive charging of the electrical double layers is also studied, for early time transients at reactive electrodes and for nonreactive blocking electrodes. Our work highlights cases where diffuse charge effects are important in the context of voltammetry, and illustrates which regimes can be approximated using simple analytical expressions and which require more careful consideration.

Glaucoma is a medical term describing a group of progressive optic neuropathies characterized by degeneration of retinal ganglion cells and retinal nerve fibre layer and resulting in changes in the optic nerve head. Glaucoma is a leading cause of irreversible vision loss worldwide. With the aging population it is expected that the prevalence of glaucoma will continue to increase. Despite recent advances in imaging and visual field testing techniques that allow establishment of earlier diagnosis and treatment initiation, significant numbers of glaucoma patients are undiagnosed and present late in the course of their disease. This can lead to irreversible vision loss, reduced quality of life, and a higher socioeconomic burden. Selection of therapeutic approaches for glaucoma should be based on careful ocular examination, patient medical history, presence of comorbidities, and awareness of concomitant systemic therapies. Therapy should also be individualized to patients’ needs and preferences. Recent developments in this therapeutic field require revisiting treatment algorithms and integration of traditional and novel approaches in order to ensure optimal visual outcomes. This article provides an overview of recent developments and practice trends in the medical management of glaucoma in Canada. A discussion of the surgical management is beyond the scope of this paper.

Batteries connected to the dc grid are exposed to a variety of currents. We explore in this paper the response of the battery to commonly seen current waveforms to understand the impact of the converter on the battery. At the frequencies considered, the battery's small-signal model is shown through impedance spectroscopy and ripple tests to be well represented by a pure resistor, and at dc currents over 2 C, Joule heating is shown to have a nonnegligible effect on the impedance. Furthermore, the amplitude of pulses that can be applied is shown to be governed by diffusion limits and the battery's state of charge.

Thermoelectric modules are an important alternative to heat engines in the harvesting of waste heat. Electrical-thermal analogs are often employed when studying heat conduction and this approach can be extended to develop a model for thermoelectric effects. In this article, the coupled thermoelectric partial differential equations are discretized using the finite-volume method; the discretization respects the coupling between the heat sink and the thermoelectric material. The new model is especially useful when an accurate picture of transients in a thermoelectric device is required. Results from the 1-D finite-volume model are shown to agree with experimental results as well as 3-D simulations using COMSOL.