Translating data and measurements from stratus to cirrus OCT in glaucoma patients and healthy subjects

Aim: our study tried to find a mathematical conversion method of the measurements obtained in Time Domain (TD) OCT to Spectral Domain (SD) OCT. Material and method: A prospective randomized, double blind study that included 244 eyes, from 121 patients (normal subjects, glaucoma suspects, glaucoma), in whom we analyzed the retinal nerve fiber layer (RNFL) and the optic disc in the same session by using TD OCT (Stratus) and SD OCT (Cirrus), was performed. The means for RNFL thickness (overall value and per quadrants), neural area and cup/ disc (C/ D) ratio, were measured. Results: We found statistically significant differences between parameters measured in TD OCT and SD OCT (p<0.001). Powerful correlations were calculated between parameters measured with the two OCT machines. Data dispersion showed a linear relation between measurements. One can use the following mathematical equations for conversion: Mean RNFL (Cirrus) = 15.77 + 0.748 x Mean RNFL (Stratus) Mean neural area (Cirrus) = 0.508 + 0.388 x Mean neural area (Stratus) Mean C/ D ratio (Cirrus) = 0.157 + 0.792 x Mean C/ D (Stratus) Conclusions: data based on our calculated mathematical conversion equations can be converted into SD OCT. Therefore, we offered a useful tool for the long term monitoring of our patients although the initial measurements in TD OCT made comparisons for patients later measured with SD OCT impossible. Abbreviations: RNFL = retinal nerve fiber layer, TD OCT = time domain optical coherence tomography, SD OCT = spectral domain optical coherence tomography, VF = visual field, CI = confidence interval, ISNT segments = inferior, superior, nasal, temporal segment.