An inter-day assessment of the ABC parameters in the evaluation of progressive keratoconus

Abstract

The progression of keratoconus is commonly determined by comparing the results of corneal tomographic measurements on different occasions. However, investigations on the repeatability of measurements are commonly performed within the same day, thus not taking the inter-day variation into account. The effect of keratoconus disease severity on the measurement error is also seldom considered. In this post hoc investigation, the parameters A, B and C in the Belin ABCD Progression Display were evaluated in relation to disease severity in intra-day and inter-day measurements. Four consecutive measurements were performed on 61 patients with keratoconus on the same day (intra-day). In another cohort, four consecutive measurements were obtained and then repeated 3 days later in 25 patients with keratoconus and 25 healthy controls (inter-day). The results suggest that the diagnosis of disease progression would benefit from inter-day measurements, and the stratification of the parameters A and C according to disease severity. It is also recommended that tomographic systems such as the Pentacam HR be modified to allow the comparison of both single measurements and the mean of replicate measurements of the parameters used in the assessment of progression of keratoconus.

Introducing a new tool for the assessment of progressive keratoconus: the Scandinavian Keratoconus Progression Application

“…The results derive from the prior publications on the interday repeatability of measurements Gustafsson, Faxén, et al 2021). The repeatability was very similar for all parameters.…”

“…In the first study , the inter-day repeatability was determined for K2 and Kmax (among other parameters). The following study (Gustafsson, Faxén, et al 2021) was based on the measurements presented in the first study, in which the results for the parameters A, B and C are presented together with an empirical assessment of the ABCD Progression Display. Comprehensive descriptions of the statistical methods used, and the resulting detection limits are given in these publications.…”

“…Detailed descriptions of patient characteristics have been given previously Gustafsson, Faxén, et al 2021). However, the magnitudes of the parameters are important as these determine the patients to which the SKPA can be applied.…”

“…In addition to the effects of disease severity, it is important to consider the inter-day repeatability of the measurements Gustafsson, Faxén, et al 2021). Progression is evaluated clinically from measurements made on different days, but detection limits are commonly based on results from studies based on same-day, or intra-day, measurements (de Luis Eguileor et al 2020;Belin et al 2017;Brunner et al 2018;Kreps et al 2020).…”

“…We have previously suggested detection limits for commonly used parameters, based on inter-day measurements. Furthermore, these detection limits benefit from being further adjusted depending on whether a single measurement is used or the mean of several measurements on each occasion, as this affects the ability to detect progression Gustafsson, Faxén, et al 2021).…”