Variability in Scheimpflug image-derived posterior elevation measurements in keratoconus and collagen-crosslinked corneas.
OBJECTIVE
To determine the variability in Scheimpflug image-derived posterior elevation measurements in eyes with keratoconus or corneal collagen crosslinking (CXL).


METHODS
Eye Institute of Thrace, Alexandroupolis, Greece.


METHODS
Prospective observational study.


METHODS
Two operators in 2 sessions obtained posterior elevation measurements using the Pentacam Scheimpflug system. Variability in measurements was assessed using Bland-Altman analysis and intraclass correlation coefficients (ICCs). Measurements were associated with a series of Scheimpflug-derived keratoconus indices using the Pearson correlation and multivariate linear-regression analysis.


RESULTS
Mean interobserver differences for the central elevation point (e1) and the highest elevation point (HEP) in the keratoconus group were -0.9 μm (95% limits of agreement [LoA], 5.7 to -7.5 μm) and 1.7 μm (95% LoA, 26 to -22.6 μm), respectively. In the CXL group, the mean differences were 0.2 μm (95% LoA, 6.0 to -5.5 μm) and -6.1 μm (95% LoA, 16.8 to -29 μm), respectively. The ICC values in the keratoconus group were satisfactory for most elevation points; the ICC values were unsatisfactory for a series of points in the lower corneal hemisphere. The ICC values for points in both hemispheres were unsatisfactory in the CXL group; HEP had adequate reproducibility. The e1 and HEP parameters correlated significantly with most Scheimpflug-derived indices (P<.05) in the keratoconus group but not in the CXL group. Regression analysis indicated that the central keratoconus index was the primary determinant of the variability in keratoconus eyes.


CONCLUSIONS
Scheimpflug-derived posterior elevation measurements had acceptable reproducibility in keratoconus eyes and post-CXL eyes. Less consistent measurements were obtained in the lower hemisphere.
Ophthalmology Department, University Hospital of Alexandroupolis, 68100 Dragana, Alexandroupolis, Greece. labiris@usa.net
Georgios
G
Labiris
Athanassios
A
Giarmoukakis
Haris
H
Sideroudi
Panagiota
P
Bougatsou
Ilias
I
Lazaridis
Vassilios P
VP
Kozobolis
D000328:Adult; D003094:Collagen / Q000378:metabolism*; D003319:Corneal Stroma / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000627:therapeutic use*; D003941:Diagnostic Techniques, Ophthalmological; D004728:Endothelium, Corneal / Q000473:pathology*; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis* / Q000188:drug therapy / Q000378:metabolism; D015588:Observer Variation; D010778:Photochemotherapy; D010781:Photography / Q000379:methods*; D017319:Photosensitizing Agents / Q000627:therapeutic use; D011446:Prospective Studies; D012256:Riboflavin / Q000627:therapeutic use; D014466:Ultraviolet Rays
D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin