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Symmetry Studies
Published in Marlos A. G. Viana, Vasudevan Lakshminarayanan, Symmetry in Optics and Vision Studies, 2019
Marlos A. G. Viana, Vasudevan Lakshminarayanan
In fitting contact lenses or prior to surgical refractive procedures such as LASIK, the parameter of primary importance is the curvature of the cornea, measured in units of inverse meter, the diopters, by an instrument called the keratometer. In the study of corneal curvature, quantities are labeled by a number of ℓ equally spaced points along a given corneal aperture, as shown in Figure 1.6 where the separation is of 10 degrees, so that V={2πk/36:k=0,…35},
Anterior segment OCT
Published in Pablo Artal, Handbook of Visual Optics, 2017
Corneal topography can be revealed by mapping the corneal thickness (pachymetry), surface elevation, or curvature/power mapping (keratometry) and plays an important role in the assessment of keratorefractive surgical procedures, corneal transplantation, or screening the corneal degenerations and dystrophies (e.g., keratoconus). There are several techniques enabling topographic description of the eye (Mejia-Barbosa and Malacara-Hernandez, 2001, Pinero, 2015). Access to volumetric data sets enables mapping the corneal thickness (corneal pachymetry). Several studies have been performed to show reproducibility of OCT pachymetry and agreement with standard instruments (Wirbelauer et al., 2002, Li et al., 2006, 2008, 2010, Pinero et al., 2008). The comparison of corneal pachymetry for normal subject and patient with keratoconus is presented in Figure 4.18 (Karnowski et al., 2011). The maps were calculated from corresponding 3-D data sets after segmentation of corneal interfaces and correction for light refraction.
Vecto-keratometry: determination of anterior corneal astigmatism in manual keratometers using power vectors
Published in Expert Review of Medical Devices, 2023
Raquel Salvador-Roger, Rosa Vila-Andrés, Vicente Micó, José J. Esteve-Taboada
The aim of this study was to propose an alternative keratometric procedure based on a power vector management of the corneal power. This new routine allows the clinician to manage corneal astigmatism in a pure power vector form, which provides several advantages over the classical method as it has been shown throughout this paper. Bland–Altman and Passing–Bablok analyses show a good agreement between the proposed method and classic techniques. Therefore, it can be assumed that there are no differences between anterior corneal astigmatism obtained by vecto-keratometry and conventional keratometry. Therefore, both methods can be mutually applied to the clinicians’ workplaces even with non-experienced examiners to facilitate their day-to-day clinical measurements. However, additional research must be done to validate this new methodology for populations with characteristics not included in this study.
Repeatability assessment of biometric measurements with different refractive states and age using a swept-source biometer
Published in Expert Review of Medical Devices, 2019
Noelia Martínez-Albert, Jose J. Esteve-Taboada, Robert Montés-Micó, Luis Fernández-Vega-Cueto, Teresa Ferrer-Blasco
The results of the present study suggest that the repeatability of biometric and keratometry parameters (AL, AQD, LT, CCT, WTW, K1, K2 and corneal astigmatism) obtained with IOLMaster 700 were not influenced by the refractive error and neither by age except AQD and LT. That means similar repeatability was offered by IOLMaster 700 within a wide range of biometric magnitudes. AQD and LT, parameters affected by the accommodation process, had better repeatability among presbyopic subjects although these differences cannot be considered as clinically significant. Finally, it must be considered that the relatively small number of eyes per group may be a limitation of this study, and therefore, our results should be confirmed by those obtained with larger sample sizes.