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Ferenc Sallo, Valerie Krivosic, Kiyoko Gocho, Michel Paques, Tunde Peto, Alan Bird, Alain Gaudric, MacTel Study Group; Adaptive optics and 'en face' OCT imaging of the outer retina in Type 2 Macular Telangiectasia. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1510.
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© ARVO (1962-2015); The Authors (2016-present)
Type 2 macular telangiectasia (type 2 MacTel) is associated with outer retinal abnormalities at and near the foveal centre. 'En face'Spectral Domain Optical Coherence Tomographic (SD-OCT) imaging of the inner segment/outer segment (IS/OS) junction layer is a validated method for following disease severity in MacTel. The resolution of commercially available SD-OCT systems is however limited. Devices equipped with adaptive optics (AO) offer superior clarity and resolution. Our aim was to examine outer retinal morphology using the two imaging modalities.
Patients were selected from the international prospective MacTel Study. SD-OCT volumesof at least 97 B-scans at 30µ intervals were acquired using a Heidelberg Spectralis OCT unit. Segmentation and 'en face' imaging of the 'IS/OS line' were performed manually, using dedicated 3D image analysis software. High resolution images of the fundus focusing on the photoreceptors were captured using an AO fundus camera (Imagine Eyes rtx1). 'En face' OCT and AO images were superimposed over images of the fundus and adjusted to attain exact correspondence. Lesions characteristic of the disease were analyzed in each imaging modality and results were compared.
Twelve eyes of 7 MacTel patients (ranging in age 55-69 years, mean age 62.7, SD=5.7 years) were examined. In 4 eyes no IS/OS break was seen on OCT and the photoreceptor mosaic was imaged clearly and appeared normal in AO images. Eight eyes demonstrated a clear defect in the IS/OS layer. In AO images, areas corresponding to a break appeared featureless. Within some larger breaks however, clustered structures similar to photoreceptors were observed. On review of the B-scans, a highly reflective material near the RPE but discontiguous with the IS/OS line was apparent in these areas. In 5 eyes a vertical restructuring of the retinal layers was seen on OCT, in these regions, photoreceptor visibility was limited in AO images.
AO imaging demonstrates abnormalities in the photoreceptor mosaic corresponding to the breaks in the IS/OS layer seen in en face OCT images in MacTel. The segmentation used for producing en face images may need to be adjusted to capture surviving photoreceptors. A quantification of photoreceptor parameters in AO images including size, reflectivity, density and/or spacing may offer further tools for detecting early signs of outer retinal changes in type 2 MacTel.
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