Posters

Comparison of four methods of measurement of central corneal thickness

Poster Details

First Author: R.Karadag TURKEY

Co Author(s):    M. Unluzeybek   H. Bayramlar   A. Yagmur   O. Cakici     

Abstract Details

Purpose:

To compare 4 methods of measurements of central corneal thickness (CCT) taken by 2 examiners in different times and to investigate intra and inter-observer differences.

Setting:

Istanbul Medeniyet University School of Medicine Goztepe Research and Training Hospital, Istanbul, Turkey

Methods:

Thirty eyes of 30 healthy volunteers aged over 20 years old were included into the study. There were 16 women and 14 men the mean age of the study group was 30.97±7.8 years.. CCT measurements were performed with 4 methods: optical low-coherence reftectometry (OLCR; LenStar LS900; Haag-Streit AG, Koeniz, Switzerland), optical coherence tomography (OCT; Topcon 3D OCT-2000, Topcon Medical System, Oakland, New Jersey, USA), noncontact specular microscopy (SM; Topcon SP-3000P; Topcon corporation, Tokyo, Japan) and corneal topography (CT; Sirius; Costruzione Strumenti Oftalmici, Florence, Italy). Two examiners sequentially performed the measurements for same persons and the measurements were repeated 1-7 days after in same manner. Each examiner took 3 measurements for each instrument and it was taken a mean of these 3 measurements. SPSS 16 package program was used for statistical analysis. As the data distributed normally, parametric tests were used and p<0.05 value was accepted as significant.

Results:

The measurements of the first observer with OCT, SM, CT and OLCR were 514.18±25.6, 525.54±34.6, 547.46±32.96, 544.25±31.16 microns at first session, and 512.60±20.85, 523.21±34.51, 546.61±31.44, 544.64±30.9 microns, at 2. session, respectively. The measurements of 2. observer with OCT, SM, CT, OLCR were 502.06±22.33, 524.53±34.60, 546.69±32.14, 544.81±30.96 microns, at 1. session, and 499.24±22.29, 524.13±33.81, 546.12±31.22, 544.45±32.49 microns, at 2. session, respectively. OCT measurements showed the smallest values at first session. There is a significant difference between OCT values and CT and OLCR values (first examiner: p<0.001, p=0.002, respectively; second: p<0.001, for both). The difference was not significant in the first examiner's OCT and SM measurements (p=972), but significant in other examiner's (p=0.029). While SM and CT measurements significantly differed from each other for both examiners (p=0.046 first examiner; p=0.033, second), there was no difference between SM and OLCR measurements (p=0.134, first examiner and p=0.066 for the second). It was not find any difference between CT and OLCR measurements (p=1.0). At first session of both examiners, there is a significant correlation between all methods (p<0.001 for all). SM, CT and OLCR measurements showed very high correlation with each other, while OCT measurements showed modest correlation with other 3 methods.

Conclusions:

Correct measurement of central corneal thickness is very important in diagnosing and managing of the patients with glaucoma as well as the patients who are candidate for refractive surgery. Currently, CCT may be taken with various methods which some of them are non-contact. The institutions may have different types of instruments measuring CCT. So, correlation between those different machines has become an important issue. In our study, the values taken by CT and OLCR are almost same in the measurements of same examiner at different time periods and also in different examiners' measurements. The difference between the measurements of these 2 methods is almost less than 1 micron. So, we conclude that CT and OLCR may be use instead of each other. In our study, we found that the confidence of OCT is lower than the other methods, since it was found a difference between the measurements of 2 examiners in same session. Additionally, the values of OCT measurements were the lowest ones. We found a difference of more than 30 microns between the measurements of OCT and the measurements of CT and OLCR. This is an important difference and may affect our decisions about corrected intraocular pressure and when making a treatment plan in refractive surgery. FINANCIAL INTEREST: NONE