Abstract

P 247

Measuring differences of the macular thickness on subjects with cystoid macular edema of various causes in TD-OCTs vs. FD-OCTs

Silvia Chaber, Horst Helbig, Maria-Andreea Gamulescu
Klinik und Poliklinik für Augenheilkunde, Universitätsklinikum Regensburg, Regensburg

Objective
When changing from previously used time-domain OCT (TD-OCT) to frequency-domain OCT (FD-OCT) the question arises how to compare measurement results. Measuring the macular thickness in healthy subjects already showed significantly different values. This difference in measurments in patients with cystoid macular edema (CME) of various causes is to be evaluated herein.
Methods
In 17 eyes of 14 patients with CME as a result of diabetic macular edema (DME, n = 12), central vein thrombosis (CVT, n = 2) and branch vein thrombosis (BVT, n = 2) OCT-examinations and calculation (mapping) of the central and surrounding retinal thickness were carried out (at a distance of 1, 3 and 6 mm from the fovea) with Stratus OCT III (Carl Zeiss Meditec Inc.; TD-OCT) as well as Spectralis-OCT (Heidelberg Engineering GmbH 2008; FD-OCT).
Results
Average central macular thickness was 378 µm in Stratus OCT III and 460 µm in Spectralis OCT. The average difference was 82 µm (21,7 %) and statistically highly significant (p < 0,001). Mean value of the automatically performed foveal single measurements showed a macular thickness of 375 µm when carried out with Stratus OCT and of 441 µm with Spectralis OCT. The average difference was 66 µm (17,6 %) and statistically significant (p = 0,03). The comparison of all 8 surrounding segments showed the following differences between both devices (TD-OCT vs. FD-OCT): Interior superior (IS) 64 µm, exterior superior (ES) 52 µm, interior inferior (II) 54 µm, exterior inferior (EI) 47 µm, interior nasal (IN) 62 µm, exterior nasal (EN) 48 µm, interior temporal (IT) 71 µm, exterior temporal (ET) 57 µm. These differences were statistically highly significant (p < 0,001) except for ES (p = 0,09).
Conclusions
The significant difference in measuring the average central macular thickness as well as in the foveal single measurements with these two devices can be explained by the fact that Stratus OCT III does not record the layers of outer segments of photoreceptor cells and the retinal pigment epithelium, whereas Spectralis OCT measurement includes both. This difference should be considered when comparing measurements from these two OCTs.

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