saprEMo: a simplified algorithm for predicting detections of electromagnetic transients in surveys

The multi-wavelength detection of GW170817 has inaugurated multi-messenger astronomy. The next step consists in interpreting observations coming from population of gravitational wave sources. We introduce saprEMo, a tool aimed at predicting the number of electromagnetic signals characterised by a specific light curve and spectrum, expected in a particular sky survey. By looking at past surveys, saprEMo allows us to constrain models of electromagnetic emission or event rates. Applying saprEMo to proposed astronomical missions/observing campaigns provides a perspective on their scientific impact and tests the effect of adopting different observational strategies. For our first case study, we adopt a model of spindown-powered X-ray emission predicted for a binary neutron star merger producing a long-lived neutron star. We apply saprEMo on data collected by XMM-Newton and Chandra and during $10^4$ s of observations with the mission concept THESEUS. We demonstrate that our emission model and binary neutron star merger rate imply the presence of some signals in the XMM-Newton catalogs. We also show that the new class of X-ray transients found by Bauer et al. in the Chandra Deep Field-South is marginally consistent with the expected rate. Finally, by studying the mission concept THESEUS, we demonstrate the substantial impact of a much larger field of view in searches of X-ray transients

Combined biomechanical and tomographic keratoconus staging: Adding a biomechanical parameter to the ABCD keratoconus staging system

Purpose This retrospective cross-sectional study evaluated the potential of an additional biomechanical parameter ‘E’ as an addition to the tomographic ABCD ectasia/keratoconus (KC) staging. Methods The Corvis Biomechanical Factor (CBiF) represents the modified linear term of the Corvis Biomechanical Index (CBI) developed based on 448 KC corneas from the Homburg Keratoconus Center (HKC). The CBiF range was divided into five stages (E0 to E4) to create a grading system according to the ABCD stages. Stage E0 was characterized by values smaller than the 2.5 percentile. The thresholds were created by dividing the CBiF range between the 2.5 and 97.5 percentiles into four groups of equal values (E1–E4). The frequency distribution of ‘E’ was analysed and independently validated based on another 860 KC corneas dataset from Milano and Rio de Janeiro (MR). The relationship between ‘E’ and the ABCD staging was analysed by cross-tabulation. The specificity of ‘E’ was assessed based on healthy controls (112|851) from both datasets (HKC|MR). Results ‘E’ was normally distributed with E0 = 37|30, E1 = 86|200, E2 = 155|354, E3 = 101|206, E4 = 69|70 in the KC group and 96.4%|90.5% of the controls classified E0 in the HKC|MR dataset, respectively. Cross-tabulation revealed that ‘E’ was most comparable to posterior corneal curvature (‘B’) in both datasets, while showing a trend towards more advanced stages in comparison to anterior corneal curvature (‘A’) and thinnest corneal thickness (‘C’). Conclusion The novel Corvis-derived parameter ‘E’ provides a biomechanical staging for ectasia/KC potentially enhancing the ABCD staging and may detect abnormalities before tomographic changes, which requires further studies

Positions of Ocular Geometrical and Visual Axes in Brazilian, Chinese and Italian Populations

ABSTRACTPurpose: To identify the relative positions of geometrical and visual axes of the eye and present a method to locate the visual center when the geometrical axis is taken as a reference.Meth..

A New Stiffness Parameter in Air Puff Induced Corneal Deformation Analysis

OCULUS Optikgerate GmbHOhio State Univ, Ophthalmol & Visual Sci & Biomed Engn, Columbus, OH 43210 USAOhio State Univ, Mech & Aerosp Engn, Columbus, OH 43210 USAUniv Liverpool, Sch Engn, Liverpool, Merseyside, EnglandUniv Insubria, Div Ophthalmol, Varese, ItalyHumanitas Clin & Res Ctr, Ctr Eye, Rozzano, ItalyVincieye Clin, Milan, ItalyRio de Janeiro Corneal Tomog & Biomech Study Grp, Rio De Janeiro, BrazilUniv Fed Sao Paulo, Ophthalmol, Rio De Janeiro, BrazilUniv Fed Sao Paulo, Ophthalmol, Rio De Janeiro, BrazilWeb of Scienc

Detection of Keratoconus With a New Biomechanical Index

To evaluate the ability of a new combined biomechanical index called the Corvis Biomechanical Index (CBI) based on corneal thickness profile and deformation parameters to separate normal from keratoconic patients

Characterization of cone size and centre in keratoconic corneas

A novel method to locate the centre of keratoconus (KC) and the transition zone between the pathological area and the rest of the corneal tissue is proposed in this study. A spherical coordinate system was used to generate a spherical height map measured relative to the centre of the optimal sphere fit, and normal to the surface. The cone centre was defined as the point with the maximum height. Second derivatives of spherical height were then used to estimate the area of pathology in an iterative process. There was mirror symmetry between cone centre locations in both eyes. The mean distance between cone centre and corneal apex was 1.45 ± 0.25 mm (0.07–2.00), the mean cone height normal to the surface was 37 ± 23 µm (2–129) and 75 ± 45 µm (5–243) in the anterior and posterior surfaces, respectively. There was a significant negative correlation between the cone height and the radius of the sphere of optimal fit (p < 0.05 for both anterior and posterior surfaces). On average, posterior cone height was larger than the corresponding anterior cone height by 37 ± 24 µm (0–158). The novel method proposed can be used to estimate the cone centre and area, and explore the changes in anterior and posterior corneal surfaces that take place with KC progression. It can help improve understanding of keratoconic corneal morphology and assist in developing customized treatments

Determination of Corneal Biomechanical Behavior in-vivo for Healthy Eyes Using CorVis ST Tonometry: Stress-Strain Index

Purpose: This study aims to introduce and clinically validate a new algorithm that can determine the biomechanical properties of the human cornea in vivo.Methods: A parametric study was conducted involving representative finite element models of human ocular globes with wide ranges of geometries and material biomechanical behavior. The models were subjected to different levels of intraocular pressure (IOP) and the action of external air puff produced by a non-contact tonometer. Predictions of dynamic corneal response under air pressure were analyzed to develop an algorithm that can predict the cornea's material behavior. The algorithm was assessed using clinical data obtained from 480 healthy participants where its predictions of material behavior were tested against variations in central corneal thickness (CCT), IOP and age, and compared against those obtained in earlier studies on ex-vivo human ocular tissue.Results: The algorithm produced a material stiffness parameter (Stress-Strain Index or SSI) that showed no significant correlation with both CCT (p &gt; 0.05) and IOP (p &gt; 0.05), but was significantly correlated with age (p &lt; 0.01). The stiffness estimates and their variation with age were also significantly correlated (p &lt; 0.01) with stiffness estimates obtained earlier in studies on ex-vivo human tissue.Conclusions: The study introduced and validated a new method for estimating the in vivo biomechanical behavior of healthy corneal tissue. The method can aid optimization of procedures that interfere mechanically with the cornea such as refractive surgeries and introduction of corneal implants