Ferrule-top probes are self-aligned all-optical devices obtained by fabricating a cantilever on the top of a ferruled optical fiber. This approach has been proven to provide a new platform for the realization of small footprint atomic force microscopes (AFMs) that adapt well to utilization outside specialized laboratories [D. Chavan et al., Rev. Sci. Instrum. 81, 123702 (2010); 82, 046107 (2011)]. In this paper we now show that ferrule-top cantilevers can be also used to develop nanoindenters. Our instrument combines the sensitivity of commercial AFM-based indentation with the ease-of-use of more macroscopic instrumented indenters available today on the market. Furthermore, the all-optical design allows smooth operations also in liquids, where other devices are much more limited and often provide data that are difficult to interpret. This study may pave the way to the implementation of a new generation user-friendly nanoindenters for the measurement of the stiffness of samples in material sciences and medical research.

PURPOSE:To develop a method to calculate the angle λ of the human eye using Zernike tilt measurements in specular reflection corneal topography. METHODS:The meaning of Zernike tilt in specular reflection corneal topography is demonstrated by measurements on translated artificial surfaces using the VU Topographer. The relationship derived from the translation experiments is used to determine the angle λ. Corneal surfaces are measured for a set of eight different fixation points, for which tilt angles ρ are obtained from the Zernike tilt coefficients. The angles ρ are used with respect to the fixation target angles to determine angle λ by fitting a geometrical model. This method is validated with Orbscan II's angle-κ measurements in 9 eyes. RESULTS:The translation experiments show that the Zernike tilt coefficient is directly related to an angle ρ, which describes a tilt orientation of the cornea and can therefore be used to derive a value for angle λ. A significant correlation exists between measured values for angle λ with the VU Topographer and the angle κ with the Orbscan II (r=0.95, P<0.001). A Bland-Altman plot indicates a mean difference of -0.52 degrees between the two instruments, but this is not statistically significant as indicated by a matched-pairs Wilcoxon signed-rank test (P≤0.1748). The mean precision for measuring angle λ using the VU topographer is 0.6±0.3 degrees. CONCLUSION: The method described above to determine angle λ is sufficiently repeatable and performs similarly to the angle-κ measurements made with the Orbscan II. RESUMEN OBJETIVO:Desarrollar un método para calcular el ángulo λ del ojo humano utilizando el coeficiente de Zernike de tilt (inclinación del frente de onda) medido mediante topografía corneal por reflexión especular. MÉTODOS:El significado del término de tilt del desarrollo de Zernike en topografía corneal especular queda demostrado por medio de medidas realizadas con el Topógrafo VU en superficies artificiales desplazadas transversalmente. La relación que se deriva de los experimentos de traslación se utiliza para determinar el ángu-lo λ. Se realizan medidas de la superficie corneal para ocho puntos de fijación diferentes. Para cada uno de ellos se obtiene el ángulo ρ de tilt (inclinación) a partir del correspondiente coeficiente de Zernike de tilt. El conjunto de ángulos ρ se utiliza con respecto a los ángulos que forman los puntos de fijación correspondientes para determinar el ángulo λ, ajustando para ello un modelo geométrico. Este método se valida comparando los resultados con medidas del ángulo κ realizadas con el Orbscan II en 9 ojos. RESULTADOS: Los experimentos de traslación demuestran que el coeficiente de Zernike de tilt está directamente relacionado con un ángulo ρ, el cual describe la inclinación global de la córnea y, por lo tanto, se puede utilizar para derivar el valor del ángulo λ. Existe una correlación significativa entre los valores del ángulo λ medidos con el Topógrafo VU y los valores del ángulo κ medidos con el Orbscan II (r=0,95; P<0,001)...