Corneal Biomechanics in Ectatic Diseases: Refractive Surgery Implications.

BACKGROUND: Ectasia development occurs due to a chronic corneal biomechanical decompensation or weakness, resulting in stromal thinning and corneal protrusion. This leads to corneal steepening, increase in astigmatism, and irregularity. In corneal refractive surgery, the detection of mild forms of ectasia pre-operatively is essential to avoid post-operative progressive ectasia, which also depends on the impact of the procedure on the cornea. METHOD: The advent of 3D tomography is proven as a significant advancement to further characterize corneal shape beyond front surface topography, which is still relevant. While screening tests for ectasia had been limited to corneal shape (geometry) assessment, clinical biomechanical assessment has been possible since the introduction of the Ocular Response Analyzer (Reichert Ophthalmic Instruments, Buffalo, USA) in 2005 and the Corvis ST (Oculus Optikgerate GmbH, Wetzlar, Germany) in 2010. Direct clinical biomechanical evaluation is recognized as paramount, especially in detection of mild ectatic cases and characterization of the susceptibility for ectasia progression for any cornea. CONCLUSIONS: The purpose of this review is to describe the current state of clinical evaluation of corneal biomechanics, focusing on the most recent advances of commercially available instruments and also on future developments, such as Brillouin microscopy.(undefined)info:eu-repo/semantics/publishedVersio

Imaging lung function in mice using SPECT/CT and per-voxel analysis.

Chronic lung disease is a major worldwide health concern but better tools are required to understand the underlying pathologies. Ventilation/perfusion (V/Q) single photon emission computed tomography (SPECT) with per-voxel analysis allows for non-invasive measurement of regional lung function. A clinically adapted V/Q methodology was used in healthy mice to investigate V/Q relationships. Twelve week-old mice were imaged to describe normal lung function while 36 week-old mice were imaged to determine how age affects V/Q. Mice were ventilated with Technegas™ and injected with (99m)Tc-macroaggregated albumin to trace ventilation and perfusion, respectively. For both processes, SPECT and CT images were acquired, co-registered, and quantitatively analyzed. On a per-voxel basis, ventilation and perfusion were moderately correlated (R = 0.58±0.03) in 12 week old animals and a mean log(V/Q) ratio of -0.07±0.01 and standard deviation of 0.36±0.02 were found, defining the extent of V/Q matching. In contrast, 36 week old animals had significantly increased levels of V/Q mismatching throughout the periphery of the lung. Measures of V/Q were consistent across healthy animals and differences were observed with age demonstrating the capability of this technique in quantifying lung function. Per-voxel analysis and the ability to non-invasively assess lung function will aid in the investigation of chronic lung disease models and drug efficacy studies

Comparison of group characteristics between 12 week old and 36 week old mice.

*<p>p<0.05, **p<0.01, ***p<0.001 by two-tailed t-test against 12 w.o. animals.</p

Regionalization of V/Q mismatching.

<p><b>A</b> Representative axial log(V/Q) slices depicting changes with age in the apex, middle, and base of the lung. The colour scale represents 2 average standard deviations from the average mean of 12w.o. animals. <b>B</b> Regional analysis of averaged log(V/Q) standard deviation values in the apex, middle, and base of the lung as well as inner and outer regions. *p<0.05, **p<0.01 by two-tailed t-test between 12 and 36w.o. groups. <b>†</b>p<0.05 apex vs. base, <b>‡</b>p<0.05 middle vs. base by one-way ANOVA with Tukey post-hoc. <b>§</b>p<0.05 by two-tailed t-test between inner and outer regions.</p

Simplified representation of the methodology used in image acquisition and processing to provide the final V/Q data sets.

<p>Simplified representation of the methodology used in image acquisition and processing to provide the final V/Q data sets.</p