Relative Repeatability Research Articles

Repeatability of lens densitometry using Scheimpflug imaging

To evaluate the repeatability of different lens densitometry analysis modes performed with Scheimpflug imaging using the Pentacam HR device. University eye hospital, Frankfurt am Main, Germany. Cross-sectional study. Eyes were analyzed under mydriasis during 2 examinations performed by the same examiner. Three single measurements were taken to assess lens densitometry via 3 modes as follows: peak (maximum), linear (vertical axis), and 3-dimensional (3-D). Measurements were also taken using 3 cylindrical reference blocks (P) with different diameters (2.0 mm, 4.0 mm, 6.00 mm) composing the whole lens depth. Repeatability was tested using Bland-Altman analysis. As statistical parameters, the coefficient of repeatability (CoR) and the relative repeatability (RR) were applied. The study analyzed 105 eyes. The CoR of the peak modus was 5.6 (RR, 29.8%); of the linear modus, 0.9 (RR, 8.8%); and of the 3-D modus, 0.36 (RR, 3.6%). The values of the P mode were lower, with a CoR between 0.19 and 0.30 (RR, 2.1%-3.3%). Lens densitometry using Scheimpflug imaging was highly repeatable. However, repeatability was dependent on the analysis mode used. Repeatability decreased with increasing opacification.

Repeatability and validity of lens densitometry measured with Scheimpflug imaging

To assess the repeatability and validity of lens densitometry derived from the Pentacam Scheimpflug imaging system. Eye Clinic, Queensland University of Technology, Brisbane, Australia. This prospective cross-sectional study evaluated 1 eye of subjects with or without cataract. Scheimpflug measurements and slitlamp and retroillumination photographs were taken through a dilated pupil. Lenses were graded with the Lens Opacities Classification System III. Intraobserver and interobserver reliability of 3 observers performing 3 repeated Scheimpflug lens densitometry measurements each was assessed. Three lens densitometry metrics were evaluated: linear, for which a line was drawn through the visual axis and a mean lens densitometry value given; peak, which is the point at which lens densitometry is greatest on the densitogram; 3-dimensional (3D), in which a fixed, circular 3.0 mm area of the lens is selected and a mean lens densitometry value given. Bland and Altman analysis of repeatability for multiple measures was applied; results were reported as the repeatability coefficient and relative repeatability (RR). Twenty eyes were evaluated. Repeatability was high. Overall, interobserver repeatability was marginally lower than intraobserver repeatability. The peak was the least reliable metric (RR 37.31%) and 3D, the most reliable (RR 5.88%). Intraobserver and interobserver lens densitometry values in the cataract group were slightly less repeatable than in the noncataract group. The intraobserver and interobserver repeatability of Scheimpflug lens densitometry was high in eyes with cataract and eyes without cataract, which supports the use of automated lens density scoring using the Scheimpflug system evaluated in the study.

Reliability and repeatability of the Pentacam on corneal curvatures

Background: The purpose of this study was to assess the intra‐observer reliability and inter‐session repeatability of the Pentacam system (Oculus, Inc.) on the simulated keratometry readings (Sim K) and peripheral corneal curvatures (PCC) at both the anterior and posterior corneal surfaces.Methods: One eye was randomly selected from each of the 39 normal subjects from the School of Optometry at The Hong Kong Polytechnic University. In the first session, three readings were taken for reliability analysis. Measurements were repeated in a second session scheduled one to two weeks later for repeatability analysis. Two approaches were used, comparing the first reading between the two sessions and comparing the average from three readings between the two sessions. Both the anterior and posterior Sim K and PCC were calculated from the tangential and axial maps. The inter‐session repeatability was reported as the coefficient of repeatability (COR = ± 1.96 × standard deviation of differences). Relative repeatability (RR) was a percentage of the ratio of COR to the mean.Results: All parameters showed good intra‐observer reliability (Cronbach's alpha ≥ 0.925; intra‐class correlation coefficient, ICC ≥ 0.804), except for the posterior power vector J45 (= 0.896; ICC = 0.742) and tangential PCC at the superior region (= 0.891; ICC = 0.732). The inter‐session repeatability on anterior Sim K (COR ≤ ±0.21-D; RR ≤ 0.48 per cent) and posterior Sim K (COR ≤ ±0.09-D; RR ≤ 1.39 per cent) was good. Axial PCC showed better repeatability than the tangential PCC. The COR from using the first approach for all the posterior PCC was within 0.23-D, while the COR reduced to within 0.16-D from using the second approach.Conclusions: The Pentacam showed good intra‐observer reliability on Sim K and PCC measurements. Averaging three readings from one visit could improve repeatability between visits.

Anterior segment biometry with the Pentacam: Comprehensive assessment of repeatability of automated measurements

To comprehensively assess the reliability of automated Pentacam (Oculus, Inc.) measurements. Flinders Eye Centre, Flinders Medical Centre, Bedford Park, South Australia, Australia. Both eyes of 35 normal volunteers were tested twice on the same day by 2 different observers. All automated values were recorded, and manual analysis of topographic maps was performed only to overrule variance in corneal thickness due to pupil decentration altering the central reference point. Repeatability was determined with Bland-Altman limits of agreement and reported as the coefficient of repeatability (COR = +/-1.96 standard deviation of differences). Relative repeatability (RR) was calculated as a percentage of the ratio of COR to the mean. Overall, repeatability was good. Corneal curvature, reported in diopters, showed good repeatability anteriorly (simulated keratometry mean COR+/-0.28D; RR=0.64%) and posteriorly (COR+/-011D; RR=1.85%). Peripheral corneal curvature was more reliable when calculated by the sagittal (axial) method (RR=1.57%) than by the tangential (meridional) method (RR=2.38%). Keratometric power deviation was less reliable (RR=16.39%). Anterior chamber measurements showed good reliability (RR=3.07%-5.68%) except for anterior chamber angle (RR=14.41%). Pupil diameter showed poor reliability (RR=25.77%). Central corneal thickness was comparable at pupil center and corneal vertex, but peripheral repeatability was much better when centered on the corneal vertex (COR+/-16.00microm; RR=2.56%) than at pupil center (COR+/-26.28microm; RR=4.23%). Pentacam corneal curvature and anterior chamber parameters were highly repeatable, but pupil measurements had poor repeatability. Peripheral pachymetry readings were affected by pupil decentration and required manual analysis using the corneal vertex as the point of reference to achieve good repeatability.