[Comparison of different optical techniques for determination of the dimensions of anterior ocular segment]

Abstract

Background: The evaluation of the anterior ocular chamber sections along the optical axis/axis of vision has been carried out using single-line partial coherence interferometry for many years. Now, new technologies such as the Scheimpflug-technique of the Pentacam (Oculus Optikgeräte GmbH, Wetzlar) and the optical coherence tomography of the Visante OCT (Carl Zeiss Meditec AG, Jena) allow the two-dimensional imaging of the anterior ocular segment in addition to goniometry and ultrasonic biomicroscopy.

Patients/materials and methods: The internal anterior chamber depth, central corneal thickness, angle-to-angle distance, and nasal and temporal anterior chamber angles of eight eyes (four patients) were examined using the Visante OCT and the Pentacam at three measurement periods within three days as part of a reproducibility study. In a comparative clinical trial on 97 eyes (53 patients), three to five measurements were made of the same parameters used in the reproducibility study, as well as external anterior chamber depths and white-to-white distances.

Results: The imaging techniques show high reproducibility with coefficients of variation up to 5.05%. The biometry instruments returned significantly different measuring results for the internal anterior chamber depth, corneal thickness and anterior chamber angle. Compared to the IOLMaster, the Visante OCT and the Pentacam produced external anterior chamber depths which were larger by 0.10 mm on average. Compared to the ACMaster, the measured internal anterior chamber depths were 0.01 mm and 0.03 mm smaller. The mean central corneal thickness measured with the Visante OCT was 3 +/- 5 microm smaller than the measured values obtained using the ACMaster. Compared to both these devices, the Pentacam produced central corneal thickness that was more than 20 microm larger. Both the Visante OCT and the Pentacam determined angle-to-angle-distances that were up to 1.3 mm smaller and up to 1.6 mm bigger than white-to-white-distances with the IOLMaster and ACMaster. On average, the anterior chamber angle measured with the Pentacam was larger 5.5 +/- 5.8 degrees (nasal) and 6.5 +/- 6.7 degrees (temporal) than the results provided by the Visante OCT.

Conclusions: The Pentacam and Visante OCT imaging biometry instruments enabled high reproducibility and highly precise measurements of intraocular distances and displays of the anterior ocular segment.