Estudio de propiedades físicas de las rocas

El objetivo de este taller es mostrar a los alumnos mediante experiencias de laboratorio sencillas y de bajo coste algunas metodologías de estudio de las propiedades físicas de las rocas como material de construcción. Las propiedades físicas de las rocas determinan su uso y comportamiento tanto como materiales de construcción como soportes de obra civil. La determinación de las propiedades físicas complementan el estudio mineralógico y textural (petrográfico) de los materiales pétreos y naturales. Las propiedades petrofísicas más importantes que se abordan en este taller son el sistema poroso (porosidad); transporte de fluidos (permeabilidad, capilaridad); propiedades mecánicas (estáticas y dinámicas); la durabilidad de las rocas frente a las sales, hielo, ataque ácido, etc.

Fitting of a New Design of Full Scleral Contact Lens in Advanced Keratoconus with Previous Implantation of Intracorneal Ring Segments

This case report reports the visual rehabilitation obtained with the fitting of a new design of full scleral contact lens (ICD 16.5 contact lens, Paragon Vision Sciences, distributed by Lenticon, Madrid, Spain) in a cornea with advanced keratoconus and previous implantation of intracorneal ring segment with a very limited effect. This eye had a refraction of –3.00 × 55° cylinder, providing a visual acuity of 0.5 LogMAR. The topographic pattern was very irregular with the presence of a significant central protrusion and a significant central corneal thinning. Some previous unsuccessful fittings have been performed with corneal and corneal-scleral lenses. A comfortable wearing was achieved with a fully scleral contact lens of 4600 μm of sagittal height, optical power of –11.25 D, and providing an apical clearance of 196 μm. A visual acuity of 0.0 LogMAR combined with a relevant aberrometric improvement was achieved with this contact lens. The patient was completely satisfied with the fitting. The result was maintained during 1 year after the fitting. Full scleral lenses are then able to provide comfortable wear and a significant increase in visual acuity combined with a significant improvement in the visual quality in eyes with advanced keratoconus.

Errors Associated to Keratoconus Grading using Systems based on Corneal Power

Purpose: To analyze and define the possible errors that may be introduced in keratoconus classification when the keratometric corneal power is used in such classification. Materials and methods: Retrospective study including a total of 44 keratoconus eyes. A comprehensive ophthalmologic examination was performed in all cases, which included a corneal analysis with the Pentacam system (Oculus). Classical keratometric corneal power (Pk), Gaussian corneal power (Pc Gauss), True Net Power (TNP) (Gaussian power neglecting the corneal thickness effect), and an adjusted keratometric corneal power (Pkadj) (keratometric power considering a variable keratometric index) were calculated. All cases included in the study were classified according to five different classification systems: Alió-Shabayek, Amsler-Krumeich, Rabinowitz-McDonnell, collaborative longitudinal evaluation of keratoconus (CLEK), and McMahon. Results: When Pk and Pkadj were compared, differences in the type of grading of keratoconus cases was found in 13.6% of eyes when the Alió-Shabayek or the Amsler-Krumeich systems were used. Likewise, grading differences were observed in 22.7% of eyes with the Rabinowitz-McDonnell and McMahon classification systems and in 31.8% of eyes with the CLEK classification system. All reclassified cases using Pkadj were done in a less severe stage, indicating that the use of Pk may lead to the classification of a cornea as keratoconus, being normal. In general, the results obtained using Pkadj, Pc Gauss or the TNP were equivalent. Differences between Pkadj and Pc Gauss were within ± 0.7D. Conclusion: The use of classical keratometric corneal power may lead to incorrect grading of the severity of keratoconus, with a trend to a more severe grading.

Interpretando ambientes sedimentarios: taller de sedimentología con arenas como actividad didáctica de Ciencias de la Tierra

El proceso de aprendizaje de las Ciencias de la Tierra, en particular en las disciplinas de la sedimentología y petrología sedimentaria, requiere de la realización de actividades prácticas, tanto en el campo como en el laboratorio. En este contexto examinar mediante lupa binocular distintos tipos de arena supone, además de un placer estético, un buen punto de partida para introducir al alumnado en la interpretación de ambientes sedimentarios. En este trabajo se propone un taller de iniciación a la reconstrucción de ambientes sedimentarios mediante el análisis de sedimentos detríticos (principalmente arenas). Se presenta una guía de procedimientos en laboratorio que incluye el análisis de los siguientes parámetros: tamaño, composición y forma de los granos, selección y color. Para vertebrar la propuesta didáctica se examinan ejemplos “tipo” de sedimentos detríticos representativos de ambientes de depósito tanto fluviales como marinos y de transición (playa), todos ellos incluidos en diferentes puntos de la geografía de la provincia de Alicante (España).