Early Changes in Corneal Epithelial Thickness after Cataract Surgery--Pilot Study.

PURPOSE: To assess early variations in central and paracentral corneal epithelial and non-epithelial thicknesses after uneventful clear corneal incision phacoemulsification. MATERIALS AND METHODS: Twenty patients with a senile cataract underwent coaxial phacoemulsification through a 2.75-mm-wide corneal incision created at 180° in a prospective cohort pilot study. Corneal sublayer thickness measurements were obtained with Fourier-domain optical coherence tomography (FD-OCT, Cirrus HD-OCT, Carl Zeiss Meditec, Inc., Dublin, CA) before and after 1 week and 1 month postoperatively. Central measurements were performed in the middle of the FD-OCT scan and in the 3-mm corneal diameter (paracentral 180° and 0° locations). Epithelial, non-epithelial and total corneal pachymetry were measured at the central and paracentral locations. RESULTS: No significant changes in epithelial thickness were seen 1 week postoperatively. However, 1 month postoperatively, the central, 180°, and 0° paracentral epithelial thicknesses (52.7 ± 3.8, 53.1 ± 5.4, and 52.7 ± 5.3 µm, respectively) decreased significantly (p < 0.01) compared to preoperatively (57.2 ± 4.8, 58.0 ± 5.7, 56.6 ± 5.3 µm, respectively). The 1-week central, 180°, and 0° paracentral non-epithelial corneal thicknesses (515.5 ± 39.6, 534.3 ± 45.6, and 521.3 ± 36.9 µm) were significantly (p < 0.01) higher than preoperatively (486.2 ± 34.7, 498.2 ± 33.8, 497.5 ± 32.3 µm, respectively). The non-epithelial corneal thickness increase was significantly (p = 0.02) greater after 1 week in the central (29.3 ± 17.2 µm) and the 180° paracentral (36.1 ± 28.7 µm) locations than at the 0° paracentral location (23.8 ± 16.5 µm). CONCLUSIONS: Immediate postoperative corneal edema following phacoemulsification irregularly affects the cornea at the sublayer level. The initial central and paracentral non-epithelial thickening is compensated by subsequent central and paracentral epithelial thinning. These initial changes occurred more markedly closest to the main incision over the entrance pupil, which may have visual implications.

Precision of high definition spectral-domain optical coherence tomography for measuring central corneal thickness.

PURPOSE: This study was intended to assess the reliability of central corneal thickness (CCT) measurements using Cirrus high-definition optical coherence tomography (HD-OCT) in healthy subjects and its accuracy compared with ultrasonic pachymetry. METHODS: Seventy-seven consecutive subjects were recruited for evaluating repeatability, and agreement between two examiners. To analyze repeatability, one examiner measured 77 eyes four times in succession. To study agreement between two observers, a second independently trained examiner obtained another CCT measurement. We also measured eyes in a subgroup of 20 patients using standard ultrasonic pachymetry. Within-subject standard deviation (S(w)), coefficient of variation (CV), limits of agreement (LoA), and intraclass correlation coefficient (ICC) data were obtained. RESULTS: For repeatability, the S(w) and precision (1.96 × S(w)) were 4.86 and 9.52 µm, respectively. Intraobserver CV was 0.89% and the ICC was 0.98 (95% confidence interval [CI], 0.97-0.99). For agreement between two examiners, the S(w) and precision were 7.58 and 14.85 µm, respectively; the CV was 1.40%. The mean difference between observers was -0.13 µm (95% CI, -1.85 to 1.58; P = 0.87). The width of the LoA was 29.64 µm. Median difference between Cirrus HD-OCT and ultrasound CCT measurements was -4.5 µm (interquartile range, -7.0-0.0; P = 0.04). CONCLUSIONS: Cirrus HD-OCT provides repeatable CCT measurements, good agreement between two independently trained examiners, and its systematic bias compared to ultrasonic pachymetry is clinically negligible. Therefore, research laboratories and eye clinics using Cirrus HD-OCT as a diagnostic imaging method, can also benefit from a reliable noncontact pachymeter when counseling patients with glaucoma and those undergoing corneal and refractive surgeries.

Comparison of central corneal thickness using optical low-coherence reflectometry and spectral-domain optical coherence tomography.

PURPOSE: To assess intraobserver and interobserver reliability of central corneal thickness (CCT) measurements using optical low-coherence reflectometry (OLCR) technology and its agreement with spectral-domain optical coherence tomography (SD-OCT). SETTING: Rio Hortega University Hospital, Valladolid, Spain. DESIGN: Evaluation of diagnostic technology. METHODS: To analyze OLCR intraobserver repeatability, 1 examiner obtained 4 successive measurements. To study interobserver reproducibility, a different examiner obtained another CCT measurement. To determine agreement with SD-OCT, the first examiner also obtained CCTs. Intraobserver and interobserver within-subject standard deviation (S(w)), coefficient of variation (CV(w)), and limits of agreement (LoA) were obtained for OLCR reliability analysis; for study agreement, data were analyzed using the paired-sample t test and the LoA were calculated. RESULTS: For OLCR intraobserver repeatability, the S(w) and precision (1.96×S(w)) were 2.33 and 4.56 µm, respectively. The intraobserver CV(w) was 0.42%. For interobserver reproducibility, the S(w) and precision were 11.59 and 22.71 µm, respectively; the CV(w) was 2.10%. The mean difference between observers was -1.35 µm (95% confidence interval [CI], -3.97 to 1.26). The width of the LoA was 45.27 µm. The mean CCT difference between OLCR and SD-OCT was 5.68±11.46 µm (95% CI, 8.29-3.08 µm; P=.0001), and the width of the LoA was 44.93 µm. CONCLUSIONS: Optical low-coherence reflectometry technology provided reliable intraobserver and interobserver CCT measurements. Although OLCR underestimated the pachymetry by less than 6 µm compared with SD-OCT, its interchangeability fell within the range of interobserver reproducibility. Both noncontact pachymetry measurements seem to be clinically useful and may be used interchangeably with minimum calibration adjustment. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.