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COMPARISON OF GANGLION CELL INNER PLEXIFORM LAYER THICKNESS BY CIRRUS AND SPECTRALIS OPTICAL COHERENCE TOMOGRAPHY IN DIABETIC MACULAR EDEMA

Purpose: Reduced thickness of the ganglion cell inner plexiform layer indicates diabetic neurodegeneration and can be assessed by spectral domain optical coherence tomography. The authors investigated the comparability of ganglion cell inner plexiform layer measurements from two spectral domain optical coherence tomography devices in patients with diabetic macular edema (DME). Methods: Analysis of optical coherence tomography data sets of eyes with and fellow eyes without DME. Macular cube scans of sufficient signal strength on Cirrus (Carl Zeiss Meditec) were compared with correlating scans on Spectralis (Heidelberg Engineering, Germany) being acquired within 1 hour. Results: Eighty-one equivalent data sets for 20 eyes with DME (20 patients; 6 female) and 33 for 9 fellow eyes without DME (9 patients; 2 female) were included from each device. In DME eyes, mean ganglion cell inner plexiform layer thicknesses were 62.5 ± 20.4 &mgr;m on Cirrus and 91.2 ± 9.3 &mgr;m on Spectralis. Ganglion cell inner plexiform layer was significantly thicker on Spectralis analyzing eyes with and without signs of DME (P < 0.001). The ganglion cell inner plexiform layer variance (54.2%) related to device differences decreased to 34.8% in eyes without DME. Conclusion: Ganglion cell inner plexiform layer data from different devices vary considerably and cannot be used interchangeably. As spectral domain optical coherence tomography is indispensable for identifying ganglion cell loss associated with diabetic neurodegeneration, clinicians should be aware of the difference when monitoring patients.