Agreement and reliability in measuring central corneal thickness with a rotating Scheimpflug–Placido system and ultrasound pachymetry

• Published in: Contact lens & anterior eye 2014-12, Vol.37 (6), p.442-446
• Main Authors: Maresca, Nunzio, Zeri, Fabrizio, Palumbo, Paolo, Calossi, Antonio
• Format: Article
• Language: English
• Subjects: Adult; Agreement; Central corneal thickness; Cornea - diagnostic imaging; Cornea - physiology; Corneal Pachymetry - instrumentation; Corneal Pachymetry - methods; Equipment Design; Equipment Failure Analysis; Female; Humans; Male; Ophthalmology; Reference Values; Reliability; Reproducibility of Results; Scheimpflug corneal tomography; Sensitivity and Specificity; Ultrasonography - instrumentation; Ultrasonography - methods; Ultrasound pachymetry; Young Adult
• ISSN: 1367-0484; 1476-5411
• DOI: 10.1016/j.clae.2014.07.009

Abstract Purpose We compare the agreement and the reliability in measuring central corneal thickness (CCT) using two different technologies. Method The right eyes of 35 healthy individuals who had a negative history of ophthalmic disease, or ocular surgery were examined. The CCT was determined sequentially with a rotating Scheimpflug camera (Sirius; CSO), and an ultrasound pachymeter (P-1; Takagi). For statistical analysis, we used the methods suggested by Bland and Altman. Results The mean values of CCT obtained from Sirius, and ultrasound were 537 ± 28 μm, and 550 ± 35 μm, respectively. There was a high correlation between Sirius and ultrasound ( r = 0.92; p < 0.001), but the difference between the two measurements was statistically significant ( t = −5.7; p < 0.00001). The precision of Sirius and ultrasound were 9.4 and 15.9 μm; repeatability 13.3 and 22.4 μm, and coefficient of variation 0.9% and 1.5%, respectively. The intraclass correlation coefficient was 0.97 for Sirius and 0.95 for ultrasound. Conclusions The average difference between corneal thickness measured with Sirius and ultrasound pachymetry was small but clinically significant. This means that the two instruments cannot be used interchangeably. Sirius showed precision and repeatability almost twice as much as ultrasound pachymetry. Confidence interval of 13.3 μm for Sirius can show variations in corneal thickness with an uncertainty value lower than 2.5% in 95% of cases. The simplicity of use, the possibility to obtain pachymetric maps, and less invasiveness make this instrument potentially useful in contact lens practice.