Comparison of central corneal thickness measurements with standard ultrasonic pachymetry and optical devices

To compare the repeatability and agreements of central corneal thickness measurements of healthy individuals obtained by Scheimpflug-Placido topographer (Sirius), anterior segment spectral domain optical coherence tomography (Spectralis) (AS-OCT), optical biometry (AL-Scan) and ultrasonic pachymetry.

Sixty-four eyes of 32 subjects with no ocular or systemic diseases were included in this study. Central corneal thickness measurements performed with Sirius, AS-OCT, optical biometry AL-Scan and ultrasonic pachymetry were compared. Bland-Altman analysis was used to demonstrate agreement between methods. Intra-examiner repeatability was assessed by using intraclass correlation co-efficients (ICCs).

Sixty-four eyes of 32 patients were enrolled (25 male and seven female). The mean age was 23.8 years (range 21-28 years). The mean central corneal thickness was 560.8 ± 37.2 μm, 528.8 ± 32.0 μm, 546.4 ± 33.8 μm, 543.4 ± 35.8 μm for the ultrasonic pachymetry, optical biometry AL-Scan, Sirius and AS-OCT values, respectively. The thickest mean central corneal thickness (560.8 ± 37.2 μm) was obtained from ultrasonic pachymetry. The thinnest mean central corneal thickness (528.8 ± 32.0 μm) was obtained from optical biometry AL-Scan. All four modalities of central corneal thickness measurements correlated closely with each other. Intra-examiner repeatability was excellent for all devices with ICCs > 0.90.

In conclusion, although measurements obtained by various methods correlate well, the measurements are not directly interchangeable. Between ultrasonic pachymetry and the three optical instruments tested, significant diferences can be seen. Therefore, the same imaging method should be used in corneal thickness follow-ups.