Accuracy of Curvature and Wavefront Aberrations of Posterior Corneal Surface, in Keratoconic and Post-CXL Corneas
Primary objective of this study was to assess the intrasession, intersession and interobserver variability of the Pentacam-derived curvature and zernike coefficients in back surface of normal, keratoconic and crosslinked corneas.
|Study Design:||Observational Model: Case Control
Time Perspective: Prospective
|Official Title:||Repeatability, Reliability and Reproducibility of Pentacam-derived Curvature and Wavefront Aberrations of Posterior Corneal Surface, in Keratoconic and Cross-linked Corneas|
- Variability of posterior corneal surface curvature and aberrometric measurements within and between sessions and within and between observers. [ Time Frame: 2 weeks ] [ Designated as safety issue: No ]The Pentacam Classic (Oculus Optikgerate GmbH, Heidelberg, Germany, software version 1.14r04) was used for the sake of the study. Three consecutive scans were obtained by two experienced operators for the assessment of intrasession and interobserver variability. The same procedure was repeated within two weeks for the assessment of intersession variability.Bland-Altman plots were used to evaluate agreement between the 2 operators. The reliability of all measurements was evaluated by means of the intraclass correlation coefficient(ICC).
|Study Start Date:||September 2011|
|Study Completion Date:||December 2011|
|Primary Completion Date:||November 2011 (Final data collection date for primary outcome measure)|
Keratoconus Group (KCG)
Keratoconus group (KCG) included patients with progressive keratoconus.
Collagen-Cross-linking group (CXLG)
Collagen-Cross-linking group (CXLG) included keratoconus patients that had been treated with uneventful corneal collagen cross-linking (CXL) at least on year prior to their enrolment in the study.
Procedure: Corneal Collagen Cross-linking (CXL)
Instillation of proparacaine hydrochloride 0.5% drops for topical anaesthesia, application of a sponge saturated with 10% alcohol to the central cornea for 20-30 seconds and subsequent de-epithelialization by means of a hockey knife. Following de-epithelialization, a mixture of 0.1% riboflavin in 20% Dextran solution was instilled to the cornea for 30 minutes (2 drops every 2 minutes) prior to the irradiation. In details, an 8.0mm diameter of central cornea was irradiated for 30 minutes by UVA light with a wavelength of 370nm and an irradiance of 3mW/cm2.The UVA radiation source that was used is the UV-XTM (IROC AG, Zurich, Switzerland). Instillation of riboflavin drops (1 drop every 2 minutes) was continued during irradiation, as well.
Normal Group (NG)
Normal group (NG) was formed by refractive surgery candidates who visited EIT's refractive surgery service for their preoperative examination. Eligibility for participation in the NG was confirmed by consecutive topographies, while all NG participants had to present uneventful ophthalmologic history, no indications of corneal pathology in slit-lamp biomicroscopy and Placido disk-based videokeratography.
The Pentacam Classic (Oculus Optikgerate GmbH, Heidelberg, Germany, software version 1.14r04) was used for the sake of the study.Three study groups were formed: 1) Normal 2) Keratoconus group (KC) included patients with progressive keratoconus and 3) Collagen-Cross-linking group (CXL) included keratoconus patients that had been treated with uneventful CXL at least on year prior to their enrollment in the study.
Three consecutive scans were obtained by two experienced operators. The same procedure was repeated within two weeks for the assessment of intersession variability. In all cases acceptable maps had at least 10.0mm of corneal coverage. Keratometry (K), asphericity (Q), best-fit toric ellipsoid radius (Rs), eccentricity (ecc) and aberrometry (6.0mm pupil diameter), were analyzed. Furthermore we calculated and studied CRMS and CLRMS in order to better appreciate the visual significance of HOAs. Precision (Pre), repeatability (COR) and intraclass correlation coefficient (ICC), were calculated for evaluating intrasession and intersession repeatability. Bland-Altman analysis was used for assessing interobserver repeatability.
|Eye Institute of Thrace (EIT)|
|Alexandroupolis, Thrace, Greece, 68100|
|Principal Investigator:||Georgios Labiris, Lecturer||Democritus University of Thrace|