3,316 research outputs found

    Barnes Hospital Bulletin

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    https://digitalcommons.wustl.edu/bjc_barnes_bulletin/1086/thumbnail.jp

    Modeling Heat Transfer in the Eye during Cataract Surgery

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    Cataract surgery is one of the most commonly performed surgical procedures in the world, and it involves using a technique called phacoemulsification. With this technique, the cloudy, crystalline lens in the eye is mechanically disrupted using a probe that vibrates at an ultrasonic frequency. However, this vibrating tip mechanism leads to frictional heat generation, which can potentially cause extensive thermal damage to fragile tissue structures surrounding the lens. In order to minimize damage due to this frictional heat, a coolant is typically used while the phaco probe is in operation. In this report, our goal is to model heat transfer in the eye using COMSOL Multiphysics software in three different scenarios: (1) under normal physiological conditions, (2) considering only the frictional heat generation from the phaco probe, (3) and considering both heat generation as well as heat removal by the coolant. Using a 2-D axisymmetric geometry to model the eye structure, we determined that using the heat source by itself results in temperatures far above the threshold of 328 K for thermal wound injury. However, with the addition of the coolant for heat removal, temperatures in the iris were lowered to less than 320 K, thereby reducing any thermal burn risk to the patient. Further analysis demonstrated that decreasing the coolant temperature or decreasing the probe?s operational power can significantly improve the safety of the procedure

    A Review of Cavitation Uses and Problems in Medicine; Invited Lecture

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    There are an increasing number of biological and bioengineering contexts in which cavitation is either utilized to create some desired effect or occurs as a byproduct of some other process. In this review an attempt will be made to describe a cross-section of these cavitation phenomena. In the byproduct category we describe some of the cavitation generated by head injuries and in artifical heart valves. In the utilization category we review the cavitation produced during lithotripsy and phacoemulsification. As an additional example we describe the nucleation suppression phenomena encountered in supersaturated oxygen solution injection. Virtually all of these cavitation and nucleation phenomena are critically dependent on the existence of nucleation sites. In most conventional engineering contexts, the prediction and control of nucleation sites is very uncertain even when dealing with a simple liquid like water. In complex biological fluids, there is a much greater dearth of information. Moreover, all these biological contexts seem to involve transient, unsteady cavitation. Consequently they involve the difficult issue of the statistical coincidence of nucleation sites and transient low pressures. The unsteady, transient nature of the phenomena means that one must be aware of the role of system dynamics in vivo and in vitro. For example, the artificial heart valve problem clearly demonstrates the importance of structural flexibility in determining cavitation occurrence and cavitation damage. Other system issues are very important in the design of in vitro systems for the study of cavitation consequences. Another common feature of these phenomena is that often the cavitation occurs in the form of a cloud of bubbles and thus involves bubble interactions and bubble cloud phenomena. In this review we summarize these issues and some of the other characteristics of biological cavitation phenomena

    Canaloplasty: current value in the management of glaucoma

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    Canaloplasty is a nonpenetrating blebless surgical technique for open-angle glaucoma, in which a flexible microcatheter is inserted within Schlemm's canal for the entire 360 degrees. When the microcatheter exits the opposite end, a 10-0 prolene suture is tied and it is then withdrawn, by pulling microcatheter back through the canal in the opposite direction. Ligation of prolene suture provides tension on the canal and facilitates aqueous outflow. The main advantage of canaloplasty is that this technique avoids the major complications of fistulating surgery related to blebs and hypotony. Currently, canaloplasty is performed in glaucoma patients with early to moderate disease and combination with cataract surgery is a suitable option in patients with clinically significant lens opacities

    Efeito da posição do bisel da caneta de facoemulsificação no endotélio corneano

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    Purpose: To compare the extent of corneal endothelial (CE) cell loss changes in two groups of eyes submitted to phacoemulsification, with the conventional bevel-up tip position in one eye and with the bevel-down tip position in the fellow eye. Methods: This prospective clinical trial comprised 25 patients with bilateral cataracts subjected to lens removal by phacoemulsification with the conventional bevel-up tip position (GI) in one eye and with the bevel-down tip position (GII) in the fellow eye. The nuclei were graded clinically on the basis of hardness. The endothelial cell count (ECC) was evaluated preoperatively and 1, 3 and 6 months postoperatively. Total surgical time, effective ultrasound time and complications were also compared between the groups. Statistical analysis was performed by the Tukey Studentized Range test, with repeated measures for the selected periods. For the other parameters a paired t test was used. Data are presented as mean ± SD, with the level of significance set at p<0.05. Results: The mean effective ultrasound time was 8.08 ± 6.75 seconds in group I and 7.00 ± 5.75 seconds in GII (P=0.1792) and total surgical time was 10.01 ± 2.46 minutes in GI and 9.86 ± 2.17 minutes in GII (p=0.6267), respectively. The paired t test revealed no statistical differences between the groups. Complications were also similar between the groups. Mean endothelial cell count loss was 6.9% in GI and 2.8% in GII at one month; 6.9% in GI and 3.6% in GII at three months and 11.9% in GI and 7.6% in GII at six months postoperatively. Comparison of endothelial cell count (ECC) showed a statistically significant difference between the groups during the postoperative period. Conclusion: The conventional bevel-up tip position has a negative effect on corneal endothelial cells compared with the bevel-down position. Since the results of other surgical parameters were similar, the bevel-down tip position should be considered as an option in non-complicated phacoemulsification.Objetivo: Comparamos duas técnicas de cirurgia de catarata. A técnica cirúrgica tradicional, em que direciona a abertura do bisel da ponteira de facoemulsificação para o endotélio corneano, com a técnica oposta, onde a reversão da posição de abertura permite o direcionamento da energia de emulsificação para o núcleo. Estudamos seus efeitos sobre a córnea e possíveis complicações. Métodos: O trabalho foi divido em quatro tempos: pré-operatório e após 30, 60 e 180 dias. Os pacientes foram divididos em dois grupos: o grupo 1, tratado com a técnica cirúrgica tradicional, com a abertura da ponteira direcionada para o endotélio, e grupo 2, que recebeu tratamento com técnica oposta, direcionada diretamente para o núcleo ou para os fragmentos nucleares. Após as cirurgias, foram estudados: perda endotelial após 30, 60 e 180 dias, tempo total de cirurgia e tempo efetivo de faco. Resultados: Os resultados intraoperatórios apresentaram o tempo efetivo de facoemulsificação no GI teve média de 8,08 segundos (DP=6,75) e no GII, média de 7,0 segundos (P=0,1792) e o tempo total de cirurgia de 10,01 ± 2,46 minutos no GI e 9,86 ± 2,17 minutos no GII (p=0,6267) respectivamente. O teste pareado não revelou diferença estatística entre os grupos. As complicações foram similares nos dois grupos. A média de perda de células endoteliais foi de 6,9% no GI e2,8% in GII com um mês; 6,9% no GI e 3,6%noGIIcom trêsmeses e 11,9% no GI e 7,6% no GII com seis meses de pós-operatório. Conclusão: Concluímos que a variação da manobra apresentada é segura e pode minimizar perdas no endotélio corneano, podendo ser uma opção na cirurgia da catarata, de acordo com as preferências pessoais do cirurgião

    Results and complications of surgeons-in-training learning bimanual microincision cataract surgery

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    PURPOSE: To evaluate visual outcomes and complications of bimanual microincision cataract surgery performed by surgeons in training. SETTING: Institute of Ophthalmology, University of Modena and Reggio Emilia, Modena, Italy. DESIGN: Prospective case series. METHODS: The corrected distance visual acuity (CDVA), astigmatism, corneal pachymetry, and endothelial cell count were evaluated before and 7 and 30 days after bimanual MICS performed by surgeons in training. Intraoperative and postoperative complications were also recorded. RESULTS: Three surgeons in training performed bimanual MICS in 150 eyes of 131 patients. There were 18 intraoperative complications (12.0%) (10 iris traumas [6.6%]; 4 capsule ruptures without vitreous loss [2.7%]; 3 capsule ruptures with vitreous loss [2.0%]; 1 intraocular lens [IOL] implantation in the sulcus due to zonular laxity [0.7%]). There were 5 postoperative complications (3.3%) (2 iris prolapses [1.3%]; 1 IOL loop malposition [0.7%]; 1 narrowing of anterior chamber [0.7%]; 1 capsulorhexis phimosis [0.7%]). Thirty days postoperatively, the mean CDVA improvement was 0.53 ± 0.20 (Snellen decimal) (P &lt; .05), the mean decrease in astigmatism was 0.09 ± 0.54 diopter (P = .29), and the mean increase in corneal pachymetry was 7.42 ± 22.01 μm (P = .12). There was statistically significant endothelial cell loss (mean 496.50 ± 469.66 cells/mm(2)) (P &lt; .05). CONCLUSIONS: Bimanual MICS performed by surgeons in training was safe and effective. Visual outcomes and complication rates were similar to those reported for coaxial cataract surgery performed by surgeons in training

    Helminthes des animaux sauvages d'Ethiopie. I. Mammifères

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    Les auteurs étudient une collection de parasites de mammifères sauvages tirés à la chasse dans le Sud et dans le Centre de l'Ethiopie entre 1973 et 1978, collection qui comprend 46 espèces différentes dont une nouvelle pour la science, Nilocotyle duplicisphinctris et 33 nouvelles pour l'Ethiopie. Quatorze d'entre elles sont communes aux mammifères domestiques et aux mammifères sauvages. L'importance de ces helminthes et leur répercussion sur le maintien de certains herbivores, rares et localisés au plateau éthiopien, sont discutée

    Similar Performance of Trabectome and Ahmed Glaucoma Devices in a Propensity Score-matched Comparison

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    Purpose: To apply propensity score matching to Ahmed glaucoma drainage implants (AGI) to trabectome-mediated ab interno trabeculectomy (AIT). Recent data suggest that AIT can produce results similar to AGI traditionally reserved for more severe glaucoma. Methods: AGI and AIT patients with at least 1 year of follow-up were included. The primary outcome measures were intraocular pressure (IOP), glaucoma medications, and a Glaucoma Index (GI) score. GI reflected glaucoma severity based on visual field, the number of preoperative medications, and preoperative IOP. Score matching used a genetic algorithm consisting of age, sex, type of glaucoma, concurrent phacoemulsification, baseline number of medications, and baseline IOP. Patients without a close match were excluded. Results: Of 152 patients, 34 AIT patients were matched to 32 AGI patients. Baseline characteristics including ethnicity, IOP, the number of medications, glaucoma type, the degree of visual field loss and GI were not significantly different between AIT and AGI. AIT had a preoperative IOP of 23.6±8.1 mm Hg compared with 26.5+10.6 mm Hg for AGI. At 12 months, the mean IOP was 15.0±9 mm Hg for AIT versus 15.0±4 mm Hg for AGI (P=0.8), whereas the number of drops was 2.3±2.2 for AIT versus 3.6±1.3 for AGI (P=0.016). Only 6 AIT patients (17.6%) required further surgery within the first 12 months versus 9 (28%) for AGI. Success, defined as IOP<21 mm Hg, <20% reduction and no reoperation, was achieved in 76% of AIT versus 69% of AGI (P=0.48). Complications occurred in 13% of AGI and 0.8% of AIT. Conclusions: A propensity score-matched comparison of AIT and AGI showed an equivalent IOP reduction through 1 year. Surprisingly, the AGI group required more glaucoma medications than the AIT group at 6 and 12 months
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