Corneal Biomechanical Properties and Anterior Segment Parameters, in Forme Fruste Keratoconus

This study has been completed.
Sponsor:
Information provided by (Responsible Party):
Georgios Labiris, Democritus University of Thrace
ClinicalTrials.gov Identifier:
NCT01448408
First received: October 5, 2011
Last updated: NA
Last verified: October 2011
History: No changes posted
  Purpose

The present study attempts to evaluate the diagnostic capacity of a) anterior segment parameters b) biomechanical metrics and c) a combination model, in differentiating Forme Fruste Keratoconus (FFK) from healthy corneas.

The study adhered to the tenets of the Declaration of Helsinki and written informed consent was given by all participants. The study was conducted at the Eye Institute of Thrace (ΕΙΤ), in Alexandroupolis, Greece. EΙΤ is a Democritus University research institute focusing primarily on the conditions of the anterior segment of the eye.

All participants underwent a complete clinical evaluation including review of medical history, visual acuity measurements, uncorrected and best corrected visual acuity, placido disc topography, Scheimpflug camera measurements, ORA measurements , slitlamp biomicroscopy and fundoscopic examination.

All study participants were divided in two groups. The FFK group (FFKG) consisted of patients with unilateral KC.

The control group (CG) was formed by refractive surgery candidates who visited EIT's outpatients service for their preoperative examination.

CRF and CH parameters were obtained while the patient was sitting on a chair in front of the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY, USA) device. Upon successful fixation of the patient's eye on a red blinking target, the operator activated the device. An air puff was released by a non-contact probe, which scanned the central area of the eye and sent a signal to the ORA. In brief, the air puff causes the cornea to move inward, past applanation, and into slight concavity. After milliseconds, the air pumps shut off, the pressure decreases, and the cornea begins to return in its normal state. The system monitors the entire process and measures two pressure values, which are determined from the inward and outward applanation processes. The aforementioned measuring procedure enables the determination of CH which is related to the viscoelastic structure of the corneal tissue, and is calculated as the difference between the two pressure values at the two applanation processes, and CRF which is indicative of the overall resistance of the cornea and is calculated as a linear function of the two pressures associated with the two applanation. In order to ensure accurate results, ORA was done four times for each eye, by the same operator. Signals that differ significantly in appearance from the other signals from the same eye were deleted.

Corneal Astigmatism (Cyl), Anterior Chamber Depth (ACD), Corneal Volume at 3mm (CV3), at 5mm (CV5), and overall (CV), Central Corneal Thickness (CCT), Thinnest Corneal Thickness (TCT) and TCT co-ordinates (TCTx, TCTy) were obtained using Pentacam. KISA index was calculated using Pentacam derived topography. Pentacam is based on a rotating Scheimpflug camera and monochromatic slit light source (a blue light emitted diode at 475 nm) which rotate together. After proper alignment of the patient's head, a fixation target is shown which guides the patients gaze. A real time image of the patient's eye is shown to the examiner on the computer screen, and the image is manually focused and centered. Acceptable maps had at least 10.0mm of corneal coverage. Moreover, images with extrapolated data in the central 9.0mm zone were excluded. Regarding the measuring procedure itself, patients were asked to blink and then look at the fixation device. In case of low-quality image, the procedure was repeated until the acceptable criteria were met.

The data from the FFKG were compared with those from the CG in separate series analyses. Receiver operating characteristics (ROC) curves were applied to determine the overall predictive accuracy of the test for each studied parameter, as described by the area under the curve. We also used this approach to identify the cut-off points for studied parameters to maximize sensitivity and specificity in discriminating FFK cases from normal corneas. Logistic regression was used to support the cut-off point identified in the ROC curve analysis. We determined a cutoff value that will gave us the best predictive fit for our sample data. Furthermore, logistic regression analysis was performed to determine the predictive capability of a model that combined both corneal biomechanical properties and pentacam derived anterior segment parameters.

Differences between groups were evaluated using the Welch modified Student's two sample t-test and Mann-Whitney U test, according to normality of distribution for each parameter. A Kolmogorov-Smirnov test of normality was applied to all variables of each group. The level of significance for each parameter was set at p<0.05. The Pearson and Spearman tests were performed in order to assess correlations between anterior segment parameters and biomechanical properties, depending on their parametric evaluation.


Condition
Keratoconus
Forme Fruste Keratoconus

Study Type: Observational
Study Design: Observational Model: Case Control
Time Perspective: Prospective
Official Title: Evaluation of the Sensitivity, Specificity, and Test Accuracy of Corneal Biomechanical Metrics, Anterior Segment Data and a Combination Model, in Differentiating Forme Fruste Keratoconus (FFK) From Healthy Corneas.

Resource links provided by NLM:


Further study details as provided by Democritus University of Thrace:

Primary Outcome Measures:
  • Sensitivity, Specificity and Predictive accuracy of CH, CRF, Cyl, ACD,CV, CV3, CV5 CCT, TCT, TCTx, TCTy and of a combination model [ Designated as safety issue: No ]
    The data from the FFKG were compared with those from the CG in separate series analysis. ROC curves were applied to determine the overall predictive accuracy of the test for each parameter. We also used this approach to identify the cut-off points for all parameters in discriminating FFK cases from normal corneas. Logistic regression was used to support the cut-off points identified in the ROC curve analysis. Furthermore, same analysis was performed to determine the predictive capability of a model that combined both corneal biomechanical properties and anterior segment parameters.


Study Start Date: May 2007
Study Completion Date: July 2011
Groups/Cohorts
Forme Fruste Keratoconus group (FFKG)
FFK eyes had to present a) no apparent signs of KC in clinical examination b) stage 0 in the Amsler-Krumeich scale, and c) demonstrate a KISA index value between 60-100%
Normal Group (CG)
Eligibility for participation in the CG was confirmed by consecutive topographies, while all CG participants had to present uneventful ophthalmologic history, no indications of corneal pathology in slit-lamp biomicroscopy and Placido disk-based videokeratography and KISA index value less than 60%, as well.

  Eligibility

Ages Eligible for Study:   18 Years to 50 Years
Genders Eligible for Study:   Both
Accepts Healthy Volunteers:   No
Sampling Method:   Non-Probability Sample
Study Population

All participants were recruited from the Outpatients Cornea service of the EIT in a consecutive if eligible basis

Criteria

Inclusion Criteria:

  • Diagnosis of Forme Fruste Keratoconus

Exclusion Criteria:

  • previous incisional eye surgery
  • corneal scars and opacities
  • a history of herpetic keratitis
  • severe eye dryness
  • pregnancy or nursing
  • current corneal infection
  • underlying autoimmune disease
  Contacts and Locations
Choosing to participate in a study is an important personal decision. Talk with your doctor and family members or friends about deciding to join a study. To learn more about this study, you or your doctor may contact the study research staff using the Contacts provided below. For general information, see Learn About Clinical Studies.

Please refer to this study by its ClinicalTrials.gov identifier: NCT01448408

Locations
Greece
Eye Institute of Thrace
Alexandroupolis, Thrace, Greece, 68100
Sponsors and Collaborators
Democritus University of Thrace
  More Information

No publications provided

Responsible Party: Georgios Labiris, Lecturer, Democritus University of Thrace
ClinicalTrials.gov Identifier: NCT01448408     History of Changes
Other Study ID Numbers: 26/27-09-2011
Study First Received: October 5, 2011
Last Updated: October 5, 2011
Health Authority: Greece: Ethics Committee

Keywords provided by Democritus University of Thrace:
Forme Fruste Keratoconus
Corneal Biomechanical properties
Anterior Segment Parameters
Diagnostic Capacity

Additional relevant MeSH terms:
Keratoconus
Corneal Diseases
Eye Diseases

ClinicalTrials.gov processed this record on August 25, 2014