Purpose To assess the repeatability and reproducibility of dynamic corneal response parameters measured by the Corvis ST (Oculus, Wetzlar, Germany). Methods One eye randomly selected from 32 healthy volunteers was examined by the Corvis ST. Three different devices were used in an alternated random order for taking three measurements at each device in each subject. Standard intraocular pressure (IOP), the biomechanical-compensated IOP (bIOP), and DCR parameters were evaluated. The within-subject standard deviation (ζw) and coefficient of variation (CV) were assessed. Results Regarding pressure indices, the ζw was below 1 mmHg for repeatability (0.98 for IOP and 0.89 for bIOP) and the CV was 6.6% for IOP and 6.1% for bIOP. For reproducibility, the ζw was around 1 mmHg (1.12 for IOP and 1.05 for bIOP) and the CV was 7.6% for IOP and 7.1% for bIOP. Most of DCR indices presented CV for repeatability below 4%. For reproducibility, the CV of most of the indices were below 6%. The deformation amplitude (DA) ratio in 1 mm and integrated radius were below 4% (1.2% and 3.8%, resp.). Conclusions The Corvis ST showed good precision (repeatability and reproducibility) for IOP measurements and for DCR in healthy eyes.
PURPOSE: To compare the long-term changes in corneal biomechanics, topography, and tomography before and 4 years after corneal cross-linking (CXL) with the Dresden protocol and correlate these changes with visual acuity. METHODS: In this longitudinal study, 18 eyes of 18 patients with progressive keratoconus who were treated with CXL were included. All patients received a standard ophthalmological examination and were examined by Placido disc–based topography, Scheimpflug tomography, and biomechanical assessments with the Corvis ST (OCULUS Optikgeräte GmbH, Wetzlar, Germany) and Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY) before and 4 years after CXL. The main outcome measures were dynamic corneal response (DCR) parameters obtained from the Corvis ST, corneal hysteresis (CH), corneal resistance factor (CRF), visual acuity, refraction, corneal curvature, and corneal thickness. RESULTS: There were no significant differences in mean visual acuity, refraction, intraocular pressure, corneal topography, corneal astigmatism in both corneal surfaces, maximum keratometry, corneal thickness at apical and thinnest points, thickness profile indices, corneal volume, and specular microscopy before and 4 years after CXL ( P > .05). Significant changes were observed in many DCR parameters, including radius at highest concavity and integrated inverse radius, both of which were consistent with stiffening. The CH and CRF values after CXL were not statistically significant. The new parameters using the Corvis ST include integrated inverse concave radius, which showed a significant decrease 1.07 ± 0.93 mm −1 , consistent with stiffening. The corneal stiffness parameter at the first applanation, Ambrósio's Relational Thickness to the horizontal profile, deformation amplitude ratio, and Corvis Biomechanical Index as a combined biomechanical screening parameter did not show significant changes. CONCLUSIONS: CXL is a minimally invasive treatment option to prevent keratoconus progression over 4 years. Pressure-derived biomechanical parameters obtained from the ORA did not show any change following CXL at 4 years of follow-up, whereas the Corvis ST DCR parameters detected changes in corneal biomechanical properties. [ J Refract Surg . 2018;34(12):849–856.]
The paper presents an original analysis method of corneal deformation images from the ultra-high-speed Scheimpflug camera (Corvis ST tonometer). Particular attention was paid to deformation frequencies exceeding 100 Hz and their reproducibility in healthy subjects examined repeatedly. A total of 4200 images with a resolution of 200 × 576 pixels were recorded. The data derived from 3 consecutive measurements from 10 volunteers with normal corneas. A new image analysis algorithm, written in Matlab with the use of the Image Processing package, adaptive image filtering, morphological analysis methods and fast Fourier transform, was proposed. The following results were obtained: (1) reproducibility of the eyeball reaction in healthy subjects with precision of 10%, (2) corneal vibrations with a frequency of 369 ± 65 Hz (3) and amplitude of 7.86 ± 1.28 µm, (4) the phase shift within two parts of the cornea of the same subject of about 150°. The result of image sequence analysis for one subject and deformations with a corneal frequency response above 100 Hz.
ZusammenfassungMachine Learning stellt insbesondere dann eine sinnvolle Alternative dar, wenn eine Datenanalyse mit wissensbasierten analytischen Methoden sehr aufwendig und schwierig ist. In solchen Fällen bietet sich auch eine Kombination aus analytischen Methoden und empirischen Methoden mittels künstlicher Intelligenz (KI) an. Die Entwicklung verschiedener Auswertefunktionen des Corvis ST ist hierfür ein konkretes Beispiel. In diesem Beitrag wird die Entwicklung dreier Screening-Parameter mittels KI beschrieben. Der Artikel zeigt, wie diese Entwicklungen im Bereich der Erkennung von klinischem und subklinischem Keratokonus sowie Glaukom-Screening klinisch hilfreich sind.
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