Eficacia del Orbscan II y Pentacam en la evaluación de los mapas de elevación en candidatos a cirugía refractiva mediante un análisis de repetibilidad

Variability of different reference bodies in normal, keratoconus, and collagen crosslinked corneas

PURPOSE

To evaluate the reproducibility of different Scheimpflug imaging-derived reference bodies in normal, keratoconus (KC), and crosslinked (CXL) eyes.

METHODS

In this prospective, observational study, 40 participants populated the control group (CG), while 33 and 34 patients formed the KC group and the CXL group, respectively. One eye was randomly selected when both were eligible. Elevation measurements were obtained using Scheimpflug camera, by applying the following reference bodies: the best fit sphere (BFS), the best fit toric ellipsoid (BFTE), the best fit toric ellipsoid with fixed eccentricity of 0.4 (BFTEF), the best fit ellipsoid (BFE), and the best fit torus, by 2 operators in 2 sessions. The variability of different reference bodies' parameters was assessed using intraclass correlation coefficient (ICC).

RESULTS

Differences between operators were nonsignificant for all reference bodies' parameters in all study groups (p>0.1). Regarding CG, BFS for both operators and BFTE for operator 1 presented the best intrasession repeatability (majority of ICCs >0.90), while average interobserver reliability was recorded for the majority of reference bodies' parameters. Regarding KC and CXL groups, BFS, BFTEF, and BFE reference bodies demonstrated the best intrasession and interobserver reproducibility (majority of ICCs >0.90) for both groups. Steep and flat radius parameters presented the best overall reproducibility, with the majority of ICCs for all reference bodies ranging above 0.90, in all study groups.

CONCLUSIONS

High variability was encountered for most reference surfaces. Ellipsotoric surfaces presented acceptable repeatability in KC and post-CXL corneas.

Repeatability and agreement of 2 Scheimpflug analyzers in measuring the central corneal thickness and anterior chamber angle, volume, and depth

PURPOSE

To evaluate the repeatability and agreement of 2 Scheimpflug tomographies (Pentacam HR, Oculus GmbH; Sirius, CSO Inc.) in measuring the central corneal thickness (CCT) and depth (ACD), volume (ACV), and angle (ACA) of the anterior chamber.

METHODS

Three consecutive measurements were performed in one eye of each subject, with both instruments. The following were evaluated: CCT, ACD, ACV, and ACA. Repeatability was assessed by the Friedman test and agreement was assessed by 4 different Wilcoxon tests for paired data.

RESULTS

The study enrolled 30 patients. With Sirius tomography the Friedman test p values for testing homogeneity across measurements was with respect to CCT 0.320, ACD 0.315, ACV 0.171, and ACA 0.020; and with Pentacam CCT 0.191, ACD 0.010, ACV 0.704, and ACA 0.150. The Wilcoxon test p values for testing the measurement homogeneity between the corneal tomography Sirius and Pentacam showed the following: ACD 0.000, ACD 0.000, ACV 0.853, and ACA 0.000.

CONCLUSIONS

The measurements may be considered substantially stable for each corneal tomography and each variable, but the 2 corneal tomographies do not produce statistically equivalent measurements.