Nanami Nakayama

Repeatability and Reproducibility of Corneal Curvature Measurements Using the Pentacam and Keratron Topography Systems

PURPOSE To compare the repeatability and reproducibility of corneal curvature measurements using the Pentacam eye scanner (Oculus Optikgeräte GmbH) and Keratron corneal topographer (Optikon 2000 SpA). METHODS Axial topography maps were used to acquire measurements. Twenty-six eyes of 26 healthy patients were measured to determine repeatability and reproducibility. Another 10 eyes of 10 healthy patients were included in a parallel study. Three measurements per eye were performed. Repeatability was assessed via the coefficient of variation. Reproducibility was assessed using Bland-Altman plots. Linear correlations were used to determine the agreement between devices. A P value < .05 was considered statistically significant. RESULTS The majority of coefficient of variations for both devices were within 1%. The coefficient of variation of the Pentacam was higher in the superior cornea (P < .01). The mean difference (95% limits of agreement) in the flattest meridian between examiners was -0.03 +/- 0.27 diopters (D) (range: -0.56 to +0.49 D) for the Pentacam and -0.08 +/- 0.21 D (range: -0.50 to +0.33 D) for the Keratron. The mean difference (95% limits of agreement) in the steepest meridian was -0.10 +/- 0.26 D (range: -0.60 to +0.41 D) for the Pentacam and -0.11 +/-0.22 D (range: -0.53 to +0.31 D) for the Keratron. The mean axial power for the central 3.0 mm of the Pentacam was statistically significantly lower than that of the Keratron (P < .01). CONCLUSIONS Although statistically significant differences were noted, both devices provided repeatable and reproducible corneal measurements centrally. Pentacam repeatability outcomes indicate that superior corneal measurements should be interpreted with caution.

Interferometry in the evaluation of precorneal tear film thickness in dry eye.

PURPOSE To compare tear film thickness between normal subjects and aqueous tear deficiency dry eye patients by tear interferometry. DESIGN Prospective case-control study. METHODS Central precorneal tear film thickness was measured noninvasively using an interference thin-film thickness measurement device (Quore MSPA1100; Mamiya-OP). Tear film thickness of 14 eyes from 14 normal subjects and of 28 eyes from 28 aqueous tear deficiency dry eye patients were compared along with noninvasively measured tear meniscus height, DR-1 (Kowa) dry eye severity grading, fluorescein and rose bengal staining scores, tear film break-up time, and Schirmer test results. Among dry eye patients, 13 eyes underwent punctal occlusion, and tear film thickness was compared before and after the surgery. RESULTS Tear film was significantly thinner in dry eye patients (2.0 ± 1.5 μm) than normal subjects (6.0 ± 2.4 μm; P < .0001). Tear film thickness showed good correlation with other dry eye examinations. After punctal occlusion, tear film thickness increased significantly from 1.7 ± 1.5 μm to 4.9 ± 2.8 μm (P = .001) with the improvement of tear meniscus height, fluorescein and rose bengal staining scores, tear film break-up time, and Schirmer test values. CONCLUSIONS Interferometric tear film thickness measurement revealed impaired precorneal tear film formation in aqueous tear deficiency dry eyes and was useful for showing the reconstruction of tear film after punctal occlusion surgery. Interferometry of precorneal tear film may be helpful for the evaluation of aqueous tear deficiency in conjunction with other dry eye examinations.