The Repeatability of Axial Length Measurements Using a Scheimpflug-based System

Area of Science:

• Ophthalmology
• Biometry
• Medical Devices

Background:

• Accurate axial length (AL) measurement is crucial for refractive error correction and intraocular lens power calculation.
• Scheimpflug-based devices offer advanced optical biometry, but their repeatability across diverse patient demographics requires thorough assessment.

Purpose of the Study:

• To evaluate the repeatability of axial length (AL) measurements using the Pentacam AXL, a Scheimpflug-based optical biometry system.
• To investigate the influence of patient age, sex, lens type, AL value, and cataract type on measurement repeatability.

Main Methods:

• Multistage cluster sampling was employed in Tehran, Iran, involving 897 eyes from 677 individuals (aged 20-91 years).
• Ocular biometry was performed thrice for each eye using the Pentacam AXL, with a 10-minute interval between measurements.
• Repeatability was assessed using the intraclass correlation coefficient (ICC) and repeatability coefficient (RC); tolerance index (TI) was used to compare repeatability across variables.

Main Results:

• The Pentacam AXL demonstrated high overall repeatability for AL measurements, with an ICC of 0.981 and an RC of 0.401.
• Repeatability was slightly better in females (ICC: 0.985) compared to males (ICC: 0.976).
• Measurement repeatability decreased with advancing age (ICC from 0.999 for <40 years to 0.973 for >60 years) and was reduced in eyes with nuclear cataracts and lower signal-to-noise ratios (SNR).

Conclusions:

• The Pentacam AXL system exhibits excellent repeatability for axial length measurements in a diverse population.
• Factors including male gender, older age, nuclear cataracts, and lower SNR are associated with decreased measurement repeatability.
• Optimizing measurement protocols and considering patient-specific factors can enhance the reliability of Pentacam AXL biometry.