Abstract
Purpose: :
Central corneal thickness (CCT) measurements (pachymetry) have become integral for the diagnosis and management of various ocular conditions. CCT measurements can be performed using ultrasonic-based or optic-based techniques. The gold standard has been ultrasonic pachymetry. Aim of this study was to assess CCT inter- and intra-operator reproducibility using 8 optical instruments (6 Spectral Domain OCT, 1 Time Domain OCT and 1 Scheimpflug Camera) and 1 ultrasonic instrument.
Methods: :
CCT was measured in the right eye of 34 randomly chosen healthy subject (18 women, 16 men, mean age 44±10,6 years) by 2 masked operators using 1 ultrasound device (Pachmate DGH55, DGH Instruments, Inc.), 6 SD-OCT (Spectral OCT/SLO, Opko; Cirrus HD-OCT, Zeiss; 3D OCT-2000, Topcon; RS-3000, Nidek; RtvUe-100, Optovue; SS-1000 CASIA, Tomey), 1 TD-OCT (Visante, Zeiss) and 1 Scheimpflug Camera (Sirius, C.T.O.). Exclusion criteria were: history of corneal and anterior segment surgery, corneal diseases, use of contact lens. Both operators repeated two consecutive measurements of each subject during the same day. Inter- and intra-operator reproducibility was evaluated by Intraclass Correlation Coefficient (ICC), Coefficient of Variation (CV) and Bland-Altman plot. Instruments-to-instruments reproducibility was determined by ANOVA for repeated measures; post hoc test for differences among instruments was also evaluated.
Results: :
Mean CCT ranged from 536.38µm (SD 42.13) to 576.92µm (SD 39.72). Visante and Sirius showed the lowest value in all measurements, 3DOCT 2000 and Spectral OCT/SLO showed the highest. While ICC and CV showed excellent inter- and intra-operator reproducibility for all optic-based devices (best results obtained by CASIA with CV<0,06% and ICC=1 for both inter- and intra-operator reproducibility), inter- and intra-operator reproducibility for Pachmate DGH55 was just good (CV<1.01% and ICC>0,87 for both inter- and intra-operator reproducibility). Bland-Altman plots confirmed these results.
Conclusions: :
Optic-based instruments showed best intra- and inter-operator reproducibility than ultrasound pachymetry. All optic-based instruments, except Spectral OCT/SLO and 3D OCT-2000, measured thinner CCT than ultrasonic-based instrument. In clinical practice CCT measurements acquired by optical and ultrasound modalities are not directly interchangeable.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • clinical (human) or epidemiologic studies: systems/equipment/techniques • cornea: clinical science