Comparing the Effect of Central Corneal Thickness (CCT) on Intraocular Pressure as Measured by Dynamic Contour Tonometry (DCT) and Non-Contact (Air-Puff) Tonometry (NCT)

Abstract

Purpose: To compare the effect of corneal thickness on intraocular pressure (IOP) measured by dynamic contour tonometer (DCT) and non-contact tonometer (NCT).Method: A total of 112 participants without history of corneal disease or current ocular hypotensive agent use were enrolled. IOP was measured by NCT and DCT sequentially on their first visit to the clinic. Central corneal thickness (CCT) was determined by an ultrasonic pachymeter at the same time. The inter-method agreement on IOP measured by these two different tonometers was assessed by the Bland-Altman method and intra-class correlation coefficient (ICC). The relationship between CCT and IOP measurement by NCT, IOP measurement by DCT, and difference in IOP measurement between the two different tonometers was assessed by simple linear regression.Results: The mean difference in IOP measurement between NCT and DCT was -1.6 mmHg (95% limit of agreement: -7.9 ~ 4.7 mmHg). There was a fair to good agreement in IOP measurement between NCT and DCT (ICC = 0.623, p ＜ 0.001). The correlation coefficients between CCT and IOP measured by NCT and DCT were 0.647 and 0.374 respectively, indicating a strong correlation between CCT and IOP in the NCT group. When CCT was less than 612.2μm, the IOP measured by NCT tended to be lower than that measured by DCT. Conversely, NCT tended to yield a higher IOP reading than DCT when CCT exceeded 612.2μm.Conclusion: IOP measured with DCT is more independent of CCT than NCT. Higher agreement between these two tonometers was noted when the CCT value came closer to 612.2μm.