Abstract
Purpose: :
To compare central corneal thickness (CCT) between automated and manual modes on the Visante anterior segment OCT, to compare CCT of the Visante with the Pachmate pachymeter, and to assess the effect of proparacaine on CCT.
Methods: :
Normal adults without any ocular disease or contact lens use were recruited. CCT was measured using the Visante anterior segment OCT, twice with the global pachymetry mode (T1 and T2) and once with the corneal high resolution mode. A blinded observer used digital calipers to measure CCT from the corneal high resolution image (M). A drop of proparacaine was placed and the CCT was measured in the global pachymetry mode (T3). After at least a 10 minute interval, another drop of proparacaine was given and CCT was measured with the Pachmate (P).
Results: :
36 eyes were analyzed. All measurements were normally distributed. Mean CCT for T1, T2, T3, M, and P were 551.8 (±33.46), 551.8 (±33.14), 553.1 (32.59), 541.7 (32.38), and 553.8 (±36.86) µm, respectively. There was good repeatability for measuring CCT: a mean difference between T1 and T2 was 0.03 µm (±3.33, p= 0.96). Measurements of CCT between T1 and M, and between T1 and P were highly correlated (Pearson correlation coefficients were 0.985 and 0.976, respectively with p<0.01). The manual mode (M) underestimated CCT compared to the automated mode (T1) with a mean difference of 10.22 µm (±5.71, p<0.001). The Visante (T1) underestimated CCT compared to the Pachmate (P) with a mean difference of 1.94µm (±8.37, p=0.17). Proparacaine did not have a strong effect on CCT, as T3 was slightly greater than T1 with a mean difference of 1.16 µm (±4.84, p=0.16).
Conclusions: :
The Visante has consistently shown high correlation with ultrasound pachymetry but has underestimated the CCT. Our findings confirm the high correlation in measuring CCT between the Visante and the Pachmate. The mean difference observed was only 1.94 µm, which is much closer than previously reported. Previous studies have proposed transient corneal edema following instillation of a topical anesthetic agent before using the ultrasound pachymeter as a reason for the underestimation of CCT by the Visante. We found that proparacaine had very little effect on the CCT. In addition, previous studies demonstrated a significant difference between the CCT measurements from the automated mode and manual mode on the Visante. Our results demonstrated a difference of only 10.22 µm between the automated and manual modes, which is smaller than reported in previous studies. In conclusion, both the automated and manual modes of the Visante can reliably and accurately measure CCT.
Keywords: cornea: clinical science • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)