Measurement Repeatability of Corneal Aberrations

2002 ◽  
Vol 18 (5) ◽  
Author(s):  
Marine Gobbe ◽  
Michel Guillon ◽  
Cecile Maissa
Keyword(s):  
Corneal Aberrations ◽  
Measurement Repeatability

scholarly journals Simultaneous Measurements of Temperature and Viscosity for Viscous Fluids Using an Ultrasonic Waveguide

Sensors ◽  
2021 ◽  
Vol 21 (16) ◽  
pp. 5543
Author(s):  
Jinrui Huang ◽  
Frederic Cegla ◽  
Andy Wickenden ◽  
Mike Coomber
Keyword(s):  
Viscous Liquid ◽  
Viscous Fluids ◽  
Fluid Temperature ◽  
Wave Propagation Velocity ◽  
Temperature Detector ◽  
Elastic Shear ◽  
Surrounding Fluid ◽  
Commercial Resistance ◽  
Measurement Repeatability ◽  
Better Than

The characterisation and monitoring of viscous fluids have many important applications. This paper reports a refined ‘dipstick’ method for ultrasonic measurement of the properties of viscous fluids. The presented method is based on the comparison of measurements of the ultrasonic properties of a waveguide that is immersed in a viscous liquid with the properties when it is immersed in a reference liquid. We can simultaneously determine the temperature and viscosity of a fluid based on the changes in the velocity and attenuation of the elastic shear waves in the waveguide. Attenuation is mainly dependent on the viscosity of the fluid that the waveguide is immersed in and the speed of the wave mainly depends on the surrounding fluid temperature. However, there is a small interdependency since the mass of the entrained viscous liquid adds to the inertia of the system and slows down the wave. The presented measurements have unprecedented precision so that the change due to the added viscous fluid mass becomes important and we propose a method to model such a ‘viscous effect’ on the wave propagation velocity. Furthermore, an algorithm to correct the velocity measurements is presented. With the proposed correction algorithm, the experimental results for kinematic viscosity and temperature show excellent agreement with measurements from a highly precise in-lab viscometer and a commercial resistance temperature detector (RTD) respectively. The measurement repeatability of the presented method is better than 2.0% in viscosity and 0.5% in temperature in the range from 8 to 300 cSt viscosity and 40 to 90 °C temperature.

Corneal aberrations andanisometropia in children

2021 ◽  
pp. 1-5
Author(s):  
Xiaoxiao Sun ◽  
Yu Zhang ◽  
Yueguo Chen
Keyword(s):  
Corneal Aberrations

Corneal Aberrations and Visual Performance After Radial Keratotomy

1998 ◽  
Vol 14 (4) ◽  
pp. 397-407 ◽  
Author(s):  
Raymond A. Applegate ◽  
Howard C. Howland ◽  
Richard P. Sharp ◽  
Andrew J. Cottingham ◽  
Richard W. Yee
Keyword(s):  
Visual Performance ◽  
Radial Keratotomy ◽  
Corneal Aberrations

Effect of Limbal Relaxing Incisions on Corneal Aberrations

2016 ◽  
Vol 32 (3) ◽  
pp. 156-162 ◽  
Author(s):  
Tamer F. Eliwa ◽  
Mona K. Abdellatif ◽  
Ismail I. Hamza
Keyword(s):  
Corneal Aberrations ◽  
Relaxing Incisions

scholarly journals Comparison of Outcomes after Phacoemulsification with Two Different Corneal Incision Distances Anterior to the Limbus

2019 ◽  
Vol 2019 ◽  
pp. 1-7
Author(s):  
Lijun Wang ◽  
Lin Zhao ◽  
Xiting Yang ◽  
Yi Zhang ◽  
Dingying Liao ◽  
...  
Keyword(s):  
Visual Acuity ◽  
Anterior Segment ◽  
Case Series ◽  
Senile Cataract ◽  
Retrospective Case ◽  
Corneal Incision ◽  
Clear Corneal Incision ◽  
Corneal Aberrations ◽  
Anterior Segment Parameters ◽  
Group B

Purpose. To compare visual performance and visual quality outcomes after phacoemulsification with two different clear corneal incision (CCI) distances anterior to the limbus in senile cataract patients. Methods. Retrospective case series. Patients who had undergone phacoemulsification were divided into two groups according to the CCI distances anterior to the limbus. The CCI distances in group A range from 1 mm to 1.5 mm, while those in group B range from 0.5 mm to 1 mm. The visual acuity, refraction, surgically induced astigmatism (SIA), corneal aberrations, anterior segment parameters, and subjective vision quality were evaluated. Results. This study enrolled 54 eyes, with 27 eyes per group. Both groups had significant improvement in postoperative uncorrected visual acuity (UCVA) and corrected distance visual acuity (CDVA) (P<0.05). There were no statistically significant between-group differences in postoperative UDVA, CDVA, SIA, corneal aberrations, anterior segment parameters, or VF-QOL questionnaire performance (P>0.05). Conclusions. The phacoemulsification with CCI distances ranging from 0.5 mm to 1.5 mm is an effective and safe therapy to senile cataract. The CCI distance anterior to the limbus that ranges from 0.5 mm to 1.5 mm is recommended for routine phacoemulsification.

Posterior corneal features in patients with Down syndrome and their relation with keratoconus

2020 ◽  
Vol 104 (12) ◽  
pp. 1683-1689 ◽  
Author(s):  
Alfredo Vega-Estrada ◽  
Chiara Fariselli ◽  
Jorge L Alio
Keyword(s):  
Down Syndrome ◽  
Clinical Study ◽  
Healthy Controls ◽  
Mean Square ◽  
Corneal Surface ◽  
Ocular Surgery ◽  
Corneal Aberrations ◽  
Significant Difference ◽  
Corneal Volume ◽  
High Order Aberrations

AimsTo characterise posterior corneal surface features in patients with Down syndrome (DS) and to compare them with healthy and mild keratoconus corneas.MethodsThis restrospective, comparative, non-randomised, clinical study included 123 eyes, divided into three groups (37 eyes of patients with DS, 46 with mild keratoconus and 40 controls), and took place at Vissum Alicante. Only patients with no previous ocular surgery, no corneal scars and no active ocular disease other than keratoconus were included. The Sirius System topographer (CSO, Firenze, Italy) was used in order to analyse posterior corneal surface keratometry, shape and keratoconus screening indices, posterior corneal aberrations, corneal volume and pachymetry.ResultsPatients with DS, when compared with healthy controls, have a steeper (mean keratometry 7 mm (KM): −6.30±0.44 vs −6.15±0.22; p<0.05) and more irregular (root mean square per unit of area: 4.5 mm 0.22±0.22 vs 0.09±0.03, p<0.001; posterior vertex of the ectatic area: 33.22±44.29 vs 10.63±2.88, p<0.001) posterior corneal surface, with higher aberrations (high-order aberrations (HOAs): 1.07±1.43 vs 0.15±0.06, p<0.001; coma-like: 0.88±1.09 vs 0.13±0.07, p<0.001) and thinnest pachymetry (497.68±26.88 vs 538.95±31.67, p<0.001). At the same time, no statistically significant difference was found between patients with DS and patients with mild keratoconus (p>0.05) in KM (−6.38±0.34), HOA (0.56±0.36), coma-like (0.51±0.34) and pachymetry (500.56±36.83).ConclusionsPosterior corneal surface of patients with DS is steeper, more irregular and shows more higher order aberrations, as well as reduced volume and thinner pachymetry than patients with healthy corneas. Additionally, posterior corneal surface in patients with DS shows similar characteristics to those found in mild keratoconus.

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