Importance of contact lens power and thickness in oxygen transmissibility

PURPOSE: The aim of this work was to study the central and peripheral thickness of several contact lenses (CL) with different powers and analyze how thickness variation affects CL oxygen transmissibility. METHODS: Four daily disposable and five monthly or biweekly CL were studied. The powers of each CL were: the maximum negative power of each brand; -6.00 D; -3.00 D; zero power (-0.25 D or -0.50 D), +3.00 D and +6.00 D. Central and peripheral thicknesses were measured with an electronic thickness gauge. Each lens was measured five times (central and 3mm paracentral) and the mean value was considered. Using the values of oxygen permeability given by the manufacturers and the measured thicknesses, the variation of oxygen transmissibility with lens power was determined. RESULTS: For monthly or biweekly lenses, central thickness changed between 0.061 ± 0.002 mm and 0.243 ± 0.002 mm, and peripheral thickness varied between 0.084 ± 0.002 mm and 0.231 ± 0.015 mm. Daily disposable lenses showed central values ranging between 0.056 ± 0.0016 mm and 0.205 ± 0.002 mm and peripheral values between 0.108 ± 0.05 and 0.232 ± 0.011 mm. Oxygen transmissibility (in units) of monthly or biweekly CL ranged between 39.4 ± 0.3 and 246.0 ± 14.4 and for daily disposable lenses the values range between 9.5 ± 0.5 and 178.1 ± 5.1. CONCLUSIONS: The central and peripheral thicknesses change significantly when considering the CL power and this has a significant impact on the oxygen transmissibility. Eyecare practitioners must have this fact in account when high power plus or minus lenses are fitted or when continuous wear is considered.

A (in)existência de apoio judiciário na arbitragem administrativa: o direito de acesso à tutela jurisdicional efetiva?

Dissertação de mestrado em Direito Administrativo

Annular flow of viscoelastic fluids: Analytical and numerical solutions

This work provides analytical and numerical solutions for the linear, quadratic and exponential Phan–Thien–Tanner (PTT) viscoelastic models, for axial and helical annular fully-developed flows under no slip and slip boundary conditions, the latter given by the linear and nonlinear Navier slip laws. The rheology of the three PTT model functions is discussed together with the influence of the slip velocity upon the flow velocity and stress fields. For the linear PTT model, full analytical solutions for the inverse problem (unknown velocity) are devised for the linear Navier slip law and two different slip exponents. For the linear PTT model with other values of the slip exponent and for the quadratic PTT model, the polynomial equation for the radial location (β) of the null shear stress must be solved numerically. For both models, the solution of the direct problem is given by an iterative procedure involving three nonlinear equations, one for β, other for the pressure gradient and another for the torque per unit length. For the exponential PTT model we devise a numerical procedure that can easily compute the numerical solution of the pure axial flow problem

Extensive subcutaneous emphysema as a presentation of ischemic colitis

Introduction . Subcutaneous emphysema is usually benign and self-limited; however, it may be associated with a life-threating situation. Case Report . An elderly woman with progressive malaise with extensive subcutaneous emphysema (cervical to abdominal wall) was observed at the emergency department. Colonic perforation was diagnosed and the patient underwent surgery. Intraoperatively, necrosis and perforation of the sigmoid colon into the retroperitoneum were found and a Hartmann procedure was performed. Conclusion . Cervical and thoracic subcutaneous emphysema may be the first sign of intra-abdominal lesion.

Deep infiltrating endometriosis of the colon causing cyclic bleeding

[Description] Endometriosis, the presence of functional endometrial tissue outside the uterus, occurs in about 3–10% of women of reproductive age and is a cause of chronic pelvic pain and infertility for some.1 Bowel involvement may be present in about 5–10% of these women, mostly affecting the rectum and distal sigmoid (over 80% of cases), and, more infrequently, the appendix, ileum and caecum. The most common lesions involve only the serosa (endometriotic implants) but they can penetrate the muscular layers of the wall, in which case they are called deep infiltrating endometriosis. (...)