Open-access operating algorithms for commercial videokeratographer and improvement of corneal sampling

We present an algorithm to process images of reflected Placido rings captured by a commercial videokeratoscope. Raw data are obtained with no Cartesian-to-polar-coordinate conversion, thus avoiding interpolation and associated numerical artifacts. The method provides a characteristic equation for the device and is able to process around 6 times more corneal data than the commercial software. Our proposal allows complete control over the whole process from the capture of corneal images until the computation of curvature radii.

Evaluación de las comunicaciones de un congreso de marketing y su posterior publicación

Tradicionalmente, la literatura ha evidenciado debilidades en el sistema de revisión por pares en el ámbito de los artículos publicados en revistas. Hasta la fecha apenas se ha dedicado atención a estas debilidades en el campo de los congresos. Este trabajo examina los factores determinantes de las evaluaciones por pares que reciben las comunicaciones de los congresos a partir de las características de sus autores y del propio manuscrito. Asimismo, analiza la relación existente entre el grado de aceptación/rechazo de las comunicaciones y la calidad de las publicaciones posteriores que se derivan de las mismas. Los resultados obtenidos en un congreso de marketing evidencian que la orientación cuantitativa, las referencias bibliográficas y las notas a pie de página influyen en la evaluación por pares de las comunicaciones. Además, se detecta que aquellas comunicaciones que son aceptadas para su presentación en el congreso, posteriormente resultan publicadas en revistas de mayor calidad.

In vivo characterization of corneal biomechanics

Interest in corneal biomechanics has increased with the development of new refractive surgery techniques aimed at modifying corneal properties and a variety of surgical options for corneal ectasia management. The human cornea behaves as soft biological material. It is a viscoelastic tissue and its response to a force applied to it depends not only on the magnitude of the force, but also on the velocity of the application. There are concerns about the limitations to measuring corneal biomechanical properties in vivo. To date, 2 systems are available for clinical use: the Ocular Response Analyzer, a dynamic bidirectional applanation device, and the Corvis ST, a dynamic Scheimpflug analyzer device. These devices are useful in clinical practice, especially for planning some surgical procedures and earlier detection of ectatic conditions, but further research is needed to connect the clinical measurements obtained with these devices to the standard mechanical properties.

Visual and optical performance and quality of life after implantation of posterior chamber phakic intraocular lens

Purpose To evaluate visual, optical, and quality of life (QoL) outcomes and intercorrelations after bilateral implantation of posterior chamber phakic intraocular lenses. Methods Twenty eyes with high to moderate myopia of 10 patients that underwent PRL implantation (Phakic Refractive Lens, Carl Zeiss Meditec AG) were examined. Refraction, visual acuity, photopic and low mesopic contrast sensitivity (CS) with and without glare, ocular aberrations, as well as QoL outcomes (National Eye Institute Refractive Error Quality of Life Instrument-42, NEI RQL-42) were evaluated at 12 months postoperatively. Results Significant improvement in uncorrected (UDVA) and best-corrected distance (CDVA) visual acuities were found postoperatively (p < 0.01), with significant reduction in spherical equivalent (p < 0.01). Low mesopic CS without glare was significantly better than measurements with glare for 1.5, 3, and 6 cycles/degree (p < 0.01). No significant correlations between higher order root mean square (RMS) with CDVA (r = −0.26, p = 0.27) and CS (r ≤ 0.45, p ≥ 0.05) were found. Postoperative binocular photopic CS for 12 cycles/degree and 18 cycles/degree correlated significantly with several RQL-42 scales. Glare index correlated significantly with CS measures and scotopic pupil size (r = −0.551, p = 0.04), but not with higher order RMS (r = −0.02, p = 0.94). Postoperative higher order RMS, postoperative primary coma and postoperative spherical aberration was significant higher for 5-mm pupil diameter (p < 0.01) compared with controls. Conclusions Correction of moderate to high myopia by means of PRL implantation had a positive impact on CS and QoL. The aberrometric increase induced by the surgery does not seem to limit CS and QoL. However, perception of glare is still a relevant disturbance in some cases possibly related to the limitation of the optical zone of the PRL.

Deep Anterior Lamellar Keratoplasty versus Penetrating Keratoplasty for Macular Corneal Dystrophy: A Randomized Trial

Purpose: To compare outcomes of big-bubble deep anterior lamellar keratoplasty (DALK) and penetrating keratoplasty (PK) for macular corneal dystrophy. Design: Prospective, randomized, interventional case series. Methods: Setting: Single hospital. Patients: Eighty-two eyes of 54 patients requiring keratoplasty for the treatment of macular corneal dystrophy without endothelial involvement were included. Main outcome measures: Operative complications, uncorrected visual acuity, best-corrected visual acuity, contrast sensitivity function, higher-order aberrations, and endothelial cell density were evaluated. Results: The DALK and PK group consisted of 35 and 41 eyes, respectively. Best-corrected visual acuity after surgery was 20/40 or better 68.5% and 70.7% of the eyes in the DALK and PK groups, respectively (P > .05). No statistically significant differences between groups were found in contrast sensitivity function with and without glare for any spatial frequency (P > .05). Significantly higher levels of higher-order aberrations were found in the DALK group (P < .01). In both groups, a progressive and statistically significant reduction in endothelial cell density was found (P < .01). At the last follow-up, the mean endothelial cell loss was 18.1% and 26.9% in DALK and PK groups, respectively (P = .03). Graft rejection episodes were seen in 5 eyes (12.1%) in the PK group, and regrafting was necessary in 3 eyes (7.3%). Recurrence of the disease was documented in 5.7% and 4.8% of the eyes in the DALK and PK groups, respectively. Conclusions: Deep anterior lamellar keratoplasty with the big-bubble technique provided comparable visual and optical results as PK and resulted in less endothelial damage, as well as eliminating endothelial rejection in macular corneal dystrophy. Deep anterior lamellar keratoplasty surgery is a viable option for macular corneal dystrophy without endothelial involvement.

Repeatability and reproducibility of corneal thickness using SOCT Copernicus HR

Purpose: The aim of this study is to determine the reliability of corneal thickness measurements derived from SOCT Copernicus HR (Fourier domain OCT). Methods: Thirty healthy eyes of 30 subjects were evaluated. One eye of each patient was chosen randomly. Images were obtained of the central (up to 2.0 mm from the corneal apex) and paracentral (2.0 to 4.0 mm) cornea. We assessed corneal thickness (central and paracentral) and epithelium thickness. The intra-observer repeatability data were analysed using the intra-class correlation coefficient (ICC) for a range of 95 per cent within-subject standard deviation (SW) and the within-subject coefficient of variation (CW). The level of agreement by Bland–Altman analysis was also represented for the study of the reproducibility between observers and agreement between methods of measurement (automatic versus manual). Results: The mean value of the central corneal thickness (CCT) was 542.4 ± 30.1 μm (SD). There was a high intra-observer agreement, finding the best result in the central sector with an intra-class correlation coefficient of 0.99, 95 per cent CI (0.989 to 0.997) and the worst, in the minimum corneal thickness, with an intra-class correlation coefficient of 0.672, 95 per cent CI (0.417 to 0.829). Reproducibility between observers was very high. The best result was found in the central sector thickness obtained both manually and automatically with an intra-class correlation coefficient of 0.990 in both cases and the worst result in the maximum corneal thickness with an intra-class correlation coefficient of 0.827. The agreement between measurement methods was also very high with intra-class correlation coefficient greater than 0.91. On the other hand the repeatability and reproducibility for epithelial measurements was poor. Conclusion: Pachymetric mapping with SOCT Copernicus HR was found to be highly repeatable and reproducible. We found that the device lacks an appropriate ergonomic design as proper focusing of the laser beam onto the cornea for anterior segment scanning required that patients were positioned slightly farther away from the machine head-rest than in the setup for retinal imaging.

Coupled Biomechanical Response of the Cornea Assessed by Non-Contact Tonometry. A Simulation Study

The mechanical response of the cornea subjected to a non-contact air-jet tonometry diagnostic test represents an interplay between its geometry, the corneal material behavior and the loading. The objective is to study this interplay to better understand and interpret the results obtained with a non-contact tonometry test. A patient-specific finite element model of a healthy eye, accounting for the load free configuration, was used. The corneal tissue was modeled as an anisotropic hyperelastic material with two preferential directions. Three different sets of parameters within the human experimental range obtained from inflation tests were considered. The influence of the IOP was studied by considering four pressure levels (10–28 mmHg) whereas the influence of corneal thickness was studied by inducing a uniform variation (300–600 microns). A Computer Fluid Dynamics (CFD) air-jet simulation determined pressure loading exerted on the anterior corneal surface. The maximum apex displacement showed a linear variation with IOP for all materials examined. On the contrary, the maximum apex displacement followed a cubic relation with corneal thickness. In addition, a significant sensitivity of the apical displacement to the corneal stiffness was also obtained. Explanation to this behavior was found in the fact that the cornea experiences bending when subjected to an air-puff loading, causing the anterior surface to work in compression whereas the posterior surface works in tension. Hence, collagen fibers located at the anterior surface do not contribute to load bearing. Non-contact tonometry devices give useful information that could be misleading since the corneal deformation is the result of the interaction between the mechanical properties, IOP, and geometry. Therefore, a non-contact tonometry test is not sufficient to evaluate their individual contribution and a complete in-vivo characterization would require more than one test to independently determine the membrane and bending corneal behavior.

Corneal biomechanics: a review

Biomechanics is often defined as ‘mechanics applied to biology’. Due to the variety and complexity of the behaviour of biological structures and materials, biomechanics is better defined as the development, extension and application of mechanics for a better understanding of physiology and physiopathology and consequently for a better diagnosis and treatment of disease and injury. Different methods for the characterisation of corneal biomechanics are reviewed in detail, including those that are currently commercially available (Ocular Response Analyzer and CorVis ST). The clinical applicability of the parameters provided by these devices are discussed, especially in the fields of glaucoma, detection of ectatic disorders and orthokeratology. Likewise, other methods are also reviewed, such as Brillouin microscopy or dynamic optical coherence tomography and others with potential application to clinical practice but not validated for in vivo measurements, such as ultrasonic elastography. Advantages and disadvantages of all these techniques are described. Finally, the concept of biomechanical modelling is revised as well as the requirements for developing biomechanical models, with special emphasis on finite element modelling.

Relationship among Corneal Biomechanics, Refractive Error, and Axial Length

Purpose: To evaluate the relationship between different ocular and corneal biomechanical parameters in emmetropic and ametropic healthy white children. Methods: This study included 293 eyes of 293 healthy Spanish children (135 boys and 158 girls), ranging in age from 6 to 17 years. Subjects were divided according to the refractive error: control (emmetropia, 99 children), myopia (100 children), and hyperopia (94 children) groups. In all cases, corneal hysteresis (CH) and corneal resistance factor (CRF) were evaluated with the Ocular Response Analyzer system. Axial length (AL) and mean corneal power were also measured by partial coherence interferometry (IOLMaster), and central corneal thickness (CCT) and anterior chamber depth were measured by anterior segment optical coherence tomography (Visante). Results: Mean (±SD) CH and CRF were 12.12 (±1.71) and 12.30 (±1.89) mm Hg, respectively. Mean (±SD) CCT was 542.68 (±37.20) μm and mean (±SD) spherical equivalent was +0.14 (±3.41) diopters. A positive correlation was found between CH and CRF (p < 0.001), and both correlated as well with CCT (p < 0.0001). Corneal resistance factor was found to decrease with increasing age (p = 0.01). Lower levels of CH were associated with longer AL and more myopia (p < 0.001 and p = 0.001, respectively). Higher values of CH were associated with increasing hyperopia. Significant differences in CH were found between emmetropic and myopic groups (p < 0.001) and between myopic and hyperopic groups (p = 0.011). There were also significant differences in CRF between emmetropic and myopic groups (p = 0.02). Multiple linear regression analysis showed that lower CH and CRF significantly associated with thinner CCT, longer AL, and flatter corneal curvature. Conclusions: The Ocular Response Analyzer corneal biomechanical properties seem to be compromised in myopia from an early age, especially in high myopia.

Estudio del daño estructural y del posterior refuerzo de un edificio afectado por asientos inducidos por la subsidencia causada por un descenso del nivel piezométrico

La subsidencia del terreno es un riesgo natural consistente en el hundimiento de la superficie terrestre que genera importantes pérdidas económicas y gran alarma social. La subsidencia del terreno puede deberse a numerosas causas, entre ellas la extracción de agua de un acuífero, que se manifiestan en la superficie del terreno mediante deformaciones verticales que pueden variar desde pocos milímetros hasta varios metros a lo largo de periodos de tiempo que varían desde minutos hasta años. El presente trabajo muestra el caso real de un edificio de sótano, bajo y cinco plantas situado en el casco urbano de Murcia (España), seriamente afectado por asientos diferenciales inducidos por la subsidencia del terreno por descenso del nivel piezométrico. El edificio, construido entre 1983 y 1986, está cimentado por medio de una losa de hormigón armado que apoya sobre un estrato de arcillas limosas de consistencia blanda. Los primeros daños se manifiestan en 1995, coincidiendo con la sequía que aquejó a la vega de Murcia entre 1991 y 1995 y que produjo descensos generalizados del nivel freático del orden de 8 m de media y que en el presente caso alcanzan los 10 m, lo que se traduce en importantes asientos de consolidación que han afectado sensiblemente a la estructura. Con objeto de estabilizar la estructura se realizó un recalce de la cimentación mediante micropilotes. Un posterior seguimiento de la estructura mediante un plan de auscultación, ha puesto de manifiesto la validez del refuerzo proyectado.

Error induced by the estimation of the corneal power and the effective lens position with a rotationally asymmetric refractive multifocal intraocular lens

AIM: To evaluate the prediction error in intraocular lens (IOL) power calculation for a rotationally asymmetric refractive multifocal IOL and the impact on this error of the optimization of the keratometric estimation of the corneal power and the prediction of the effective lens position (ELP). METHODS: Retrospective study including a total of 25 eyes of 13 patients (age, 50 to 83y) with previous cataract surgery with implantation of the Lentis Mplus LS-312 IOL (Oculentis GmbH, Germany). In all cases, an adjusted IOL power (PIOLadj) was calculated based on Gaussian optics using a variable keratometric index value (nkadj) for the estimation of the corneal power (Pkadj) and on a new value for ELP (ELPadj) obtained by multiple regression analysis. This PIOLadj was compared with the IOL power implanted (PIOLReal) and the value proposed by three conventional formulas (Haigis, Hoffer Q and Holladay). RESULTS: PIOLReal was not significantly different than PIOLadj and Holladay IOL power (P>0.05). In the Bland and Altman analysis, PIOLadj showed lower mean difference (-0.07 D) and limits of agreement (of 1.47 and -1.61 D) when compared to PIOLReal than the IOL power value obtained with the Holladay formula. Furthermore, ELPadj was significantly lower than ELP calculated with other conventional formulas (P<0.01) and was found to be dependent on axial length, anterior chamber depth and Pkadj. CONCLUSION: Refractive outcomes after cataract surgery with implantation of the multifocal IOL Lentis Mplus LS-312 can be optimized by minimizing the keratometric error and by estimating ELP using a mathematical expression dependent on anatomical factors.

Clinical Validation of Adjusted Corneal Power in Patients with Previous Myopic Lasik Surgery

Purpose. To validate clinically a new method for estimating the corneal power (P,) using a variable keratometric index (nkadj) in eyes with previous laser refractive surgery. Setting. University of Alicante and Medimar International Hospital (Oftalmar), Alicante, (Spain). Design. Retrospective case series. Methods. This retrospective study comprised 62 eyes of 62 patients that had undergone myopic LASIK surgery. An algorithm for the calculation of 11kadj was used for the estimation of the adjusted keratometric corneal power (Pkadj). This value was compared with the classical keratometric corneal power (Pk), the True Net Power (TNP), and the Gaussian corneal power (PcGauss). Likewise, Pkadj was compared with other previously described methods. Results. Differences between PcGauss and P, values obtained with all methods evaluated were statistically significant (p < 0.01). Differences between Pkadj and PcGauss were in the limit of clinical significance (p < 0.01, loA [ - 0.33,0.60] D). Differences between Pkadj and TNP were not statistically and clinically significant (p = 0.319, loA [- 0.50,0.44] D). Differences between Pkadj and previously described methods were statistically significant (p < 0.01), except with PcHaigisL (p = 0.09, loA [ - 0.37,0.29] D). Conclusion. The use of the adjusted keratometric index (nkadj) is a valid method to estimate the central corneal power in corneas with previous myopic laser refractive surgery, providing results comparable to PcHaigisL.

Interaction between diurnal variations of intraocular pressure, pachymetry, and corneal response to an air puff: Preliminary evidence

Diurnal changes in corneal geometry, pachymetry, and intraocular pressure (IOP) in a healthy eye were recorded. The deformation response to an air puff was simulated using 3 levels of corneal stiffness. The response was dependent on IOP and pachymetry and not only on the biomechanical properties of the cornea. Similarly, the maximum variability due to the diurnal changes in pachymetry and IOP in the corneal displacement generated by the air puff was found to reach 5%. Therefore, diurnal changes in IOP and corneal thickness were able to induce some variability in the air puff–based corneal deformation response. This potential variability should be considered when the biomechanical properties of the cornea are analyzed with air-puff devices.

Positional accommodative intraocular lens power error induced by the estimation of the corneal power and the effective lens position

Purpose: To evaluate the predictability of the refractive correction achieved with a positional accommodating intraocular lenses (IOL) and to develop a potential optimization of it by minimizing the error associated with the keratometric estimation of the corneal power and by developing a predictive formula for the effective lens position (ELP). Materials and Methods: Clinical data from 25 eyes of 14 patients (age range, 52–77 years) and undergoing cataract surgery with implantation of the accommodating IOL Crystalens HD (Bausch and Lomb) were retrospectively reviewed. In all cases, the calculation of an adjusted IOL power (PIOLadj) based on Gaussian optics considering the residual refractive error was done using a variable keratometric index value (nkadj) for corneal power estimation with and without using an estimation algorithm for ELP obtained by multiple regression analysis (ELPadj). PIOLadj was compared to the real IOL power implanted (PIOLReal, calculated with the SRK-T formula) and also to the values estimated by the Haigis, HofferQ, and Holladay I formulas. Results: No statistically significant differences were found between PIOLReal and PIOLadj when ELPadj was used (P = 0.10), with a range of agreement between calculations of 1.23 D. In contrast, PIOLReal was significantly higher when compared to PIOLadj without using ELPadj and also compared to the values estimated by the other formulas. Conclusions: Predictable refractive outcomes can be obtained with the accommodating IOL Crystalens HD using a variable keratometric index for corneal power estimation and by estimating ELP with an algorithm dependent on anatomical factors and age.

Manobrar a vertigem posicional paroxística benigna do canal semicircular posterior

Trabalho Final do Curso de Mestrado Integrado em Medicina, Faculdade de Medicina, Universidade de Lisboa, 2014