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Maher Saleh, Alois Bully, Mathieu Flores; Cone density estimates derived from the reflectivity of the inner segment ellipsoid band on en-face spectral domain OCT . Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4939.
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© ARVO (1962-2015); The Authors (2016-present)
The objective of this project is to develop, test and validate a software allowing to estimate photoreceptor density derived from the inner segment ellipsoid (ISe) band reflectivity on en-face OCT.
Eight eyes displaying various degrees of outer retinal impairment (five eyes with resolved central serous chorioretinopathy, one with hydroxychloroquine toxicity, and two healthy eyes) were imaged using a spectral-domain OCT (Spectralis, Heidelberg, Heidelberg Engineering, Germany). En-face OCT was generated from horizontal transverse scans, 11µ apart, with a resolution of 384A scan/Bscan. Segmentation of the Ise band was automatically performed with the Heidelberg Explorer plug-in provided by the manufacturer. The relevance of the “PR1” segmentation line was checked by two readers. At the same time, a software running on Matlab, (Matlab, Mathworks Inc., Natick, USA) that transforms the grey level into cone density was developed. Its algorithm is based on a previous work comparing OCT reflectivity and adaptive optics. The program determines the cone density in a ring ranging from 1.5 to 2 degrees of eccentricity from the fovea. In order to validate the estimates, cone densities were measured in the same eyes, in a blind manner, by an independent observer, using adaptive optics (AOdetect v0.2, Imagine Eyes, Orsay, France).
Thirty five points of comparison were obtained. The program estimates were closely correlated with the results of the reference counting method, i.e. adaptive optics (r2=0.81, p<0.05). Bland-Altman plot displayed a moderate estimated bias of 204±2660 cellules/mm2(CI95%: 5008-5418). The estimatation was considered relevant (defined as a difference of more and less 10%) in 80% of the cases.
It has become possible to estimate cone density with an OCT device currently used in routine practice, at least in a defined retinal area. Improvement in the acquisition procedure (resolution, artefact management...) will eventually improve the accuracy of the results.
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