Repeatability and agreement of higher order aberrations for different devices

Abstract

Purpose : The aim of the study was to compare the most important higher order aberrations provided by the Pentacam AXL Wave and the iTrace.

Methods : Prospective, randomised study with three consecutive measurements per eye and each device, the Pentacam AXL Wave (Oculus) and the iTrace (Tracey Technologies). Each patient completed all measurements at the same day and all measurements had good quality scores.
Forty two patients (34 right and 38 left eyes) ranging in age from 20 to 63 year (mean age was 36 ±14 years) took part in this study. None of the patients had any known ocular pathology, all eyes were phakic.
The most crucial higher order aberrations (trefoil 30° and 0°, coma 90° and 0° and spherical aberration) of the complete eye were analysed for a 3mm zone. Repeatability was assessed with standard deviation (SD). Bland-Altman analysis was used to assess agreement between the devices.

Results : Repeatability
The mean values of the analysed HOAs and their standard deviations are: trefoil 30° - Wave -0,021µm ±0,011, iTrace -0,016µm ±0,013; trefoil 0° - Wave -0,003µm ±0,009, iTrace -0,001µm ±0,012; coma 90° - Wave 0,005µm ±0,011, iTrace 0,008µm ±0,012; coma 0° - Wave 0,001µm ±0,009, iTrace 0,008µm ±0,012; sph aberr - Wave 0,011µm ±0,005, iTrace 0,01µm ±0,007. A paired-samples t-test was conducted to compare the means of the devices. Only the differences of the coma 0° were statistically different (p<.05).
Agreement
A Bland-Altman analysis revealed the following mean differences, standard deviations and limits of agreement for the two devices (mean_DIFF = mean_WAVE - mean_iTRACE): trefoil 30° - mean_DIFF -0,005µm ±0,029, LOA_low -0,062, LOA_upp 0,052; trefoil 0° - mean_DIFF -0,002µm ±0,029, LOA_low -0,059, LOA_upp 0,055; coma 90° - mean_DIFF -0,015µm ±0,027, LOA_low-0,068, LOA_upp 0,038; coma 0° - mean_DIFF -0,006µm ±0,032, LOA_low -0,068, LOA_upp 0,056; sph aberr - mean_DIFF 0,002µm ±0,017, LOA_low -0,031, LOA_upp 0,035.

Conclusions : In general, the higher order aberrations were rather low what can be explained by the relatively young and healthy study population. The small standard deviations indicate good repeatability for both devices, however, those of the Pentacam AXL Wave tended to be smaller than the ones of the iTrace. Agreement between the devices was high even so this result remains to be confirmed for larger zones and pathological eyes, e.g. keratoconus.

This is a 2021 ARVO Annual Meeting abstract.