Abstract

P 169

Characterization of optic atrophy-induced changes in thickness of macular layers by quantification of the reflectivity profile of OCT scans

Elisabeth Kühn, Helmut Tegetmeyer
Klinik und Poliklinik für Augenheilkunde, Universitätsklinikum Leipzig, Leipzig

Objective
Integrated standard system software of presently available equipment for optical coherence tomography (OCT) provides the measurement of the thickness of the retinal nerve fibre layer (RNFL) and of the macular volume (MV). However, a thickness analysis of individual retinal layers is not possible so far. Therefore, changes in macular thickness as a consequence of optic atrophy are to be characterised and attributed to the individual macular layers by means of the quantification of axial reflectivity profiles of exported OCT scans.
Methods
OCT scans of the macula were obtained by means of fast scan protocols using Stratus OCT 3000 (Carl Zeiss Meditec) from patients with diagnostically confirmed optic atrophy and from normal control subjects. The 6 radial scans were displayed as gray tone pictures and exported as JPEG images in each subject.
Using a freeware image processing software  (ImageJ, NIH), the axial reflectivity profiles of the radial scans were determined and averaged from all the 12 measuring points at a distance of 1.5mm from the foveola. Since the transversal width of the profile amounted to 180µm, at least 3 adjacent axial scans were collected at each data point. The characteristic profile sequence of 5 intensity maxima (nerve fibre layer, inner plexiform layer, outer plexiform layer, junction between inner and outer photoreceptor segments, retinal pigment epithelium) and 4 intensity minima (ganglion cell layer, inner nuclear layer, outer nuclear layer and inner photoreceptor segments, outer photoreceptor segments) was attributed to the location of the individual macular layers from the inside to the outside.
Results
The changes in thickness of the individual retinal layers could be characterized from the axial reflectivity profiles by the distance changes of adjacent maxima or minima with a satisfactory reproducibility. Thus, in patients with optic atrophy, distinct decreases in thickness of the 3 inner macular layers could be demonstrated.
Conclusions
The analysis of axial reflectivity profiles from exported JPEG images of macular OCT scans allows the quantification of the thickness of individual macular layers and of their changes as a result of optic atrophy.

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