The Interday Repeatability of Parameters for the Assessment of Progressive Disease in Subjects With Less Advanced Keratoconus

Ingemar Gustafsson,Anders Bergström,Anna Cardiakides,Anders Ivarsen,Jesper Østergaard Hjortdal

doi:10.1016/j.ajo.2020.12.028

Ingemar Gustafsson, Anders Bergström + Show 3 more

Open Access

https://doi.org/10.1016/j.ajo.2020.12.028

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Abstract

To evaluate the interday repeatability in the measurement of parameters used for the detection of progression of keratoconus by prediction limits (PL) for single measurements, and the repeatability coefficient (RC) for the mean of replicate measurements. Prospective reliability analysis for cases and control eyes. Twenty-five eyes in 25 subjects with KC and 25 eyes in 25 healthy controls were included. Four consecutive measurements were made, 3days apart, with a Pentacam HR tomographic instrument (denoted the Pentacam) and a Nidek ARK 560-A auto-keratometer (denoted the keratometer). Main outcome measures were the intra- and interday RC of parameters used in the detection of progression of keratoconus. The most repeatable parameter obtained with the Pentacam was the curvature power of the central flat meridian (K1, 0.44 D [RC], -0.55 to 0.60 diopter [D] [PL]), followed by the central steep meridian (K2, 0.72 D [RC], -0.90 to 0.94 D [PL]). The interday repeatability of K1 and K2 was similar when using the keratometer (K1, 0.32 D [RC], -0.66 to 0.57 D [PL], K2, 0.93 D [RC], -1.36 to 1.08 D [PL]). The interday repeatability of the curvature power of the steepest point (Kmax, 0.84 D [RC], -0.90 to 1.11 D [PL]) would benefit from being stratified: RC= 0.44 D and PL= -0.49 to 0.67 D for Kmax < 49.0 D, and RC= 1.08 D and PL= -1.19 to 1.42 D for Kmax ≥ 49.0 D. The interday repeatability of measurements, single or replicate, in subjects with keratoconus should be considered when diagnosing progressive disease. K1 exhibited the best intraday repeatability. Kmax benefits from being stratified according to disease severity.

Highlights

K ERATOCONUS IS A CORNEAL DISEASE THAT CAN cause severe visual impairment
The interday comparison between single measurements is presented as prediction limits (PL), and the mean of 4 measurements is presented as repeatability coefficient (RC)
As statistical models assume a constant measurement error, the standard deviation (SD) were plotted against the magnitude of the investigated parameters and the association analyzed using Kendall’s Tau-b in the preanalysis of data.[15]

Summary

Introduction

K ERATOCONUS IS A CORNEAL DISEASE THAT CAN cause severe visual impairment. Growing evidence suggests that corneal cross-linking (CXL) halts the progression of the disease, preventing further visual deterioration.[1,2] The general indication for CXL is progressive KC, as stated in the US FDA approval of CXL in 2016. Several studies have been carried out to investigate RC in measurements of the parameters used in the detection of progressive keratoconus.[4,5,6,7] RC is usually calculated based on measurements on the same day, rather than on different days.[8] The evaluation of the interday repeatability in subjects with keratoconus is of the utmost importance, as progression is diagnosed over time. Subjects with keratoconus stage

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