OUTER FOVEAL DEFECTS IN TYPE-2 MACULAR TELANGIECTASIA

Outer foveal defects in Macular Telangiectasia-2 are rare. These defects have been observed to involve mainly the ellipsoid and interdigitation zones and mostly spare the external limiting membrane at the fovea. Purpose: To report characteristics of outer foveal defects (OFDs) in type-2 macular telangiectasia (MacTel) on spectral domain optical coherence tomography. Methods: This was a single-center observational study. From a registry of 745 patients with MacTel, patients with OFDs were characterized. All patients underwent multimodal imaging including color fundus photography, confocal blue reflectance, fundus autofluorescence, and spectral domain optical coherence tomography. Staging of eyes was done using the Gass and Blodi classification. Spectral domain optical coherence tomography characteristics in the central 1 mm of the macula in eyes with OFD are reported. Results: Outer foveal defect was observed in 21 eyes of 15/745 (2%) patients with MacTel. These defects were bilateral in 6/15 (40%) patients and seen in stage 2 MacTel eyes. In order of prevalence, foveal parameters seen in OFD included hyper-reflective dots in outer retina in 19/21 (90%), ellipsoid zone loss in 18/21 (86%) eyes, interdigitation zone loss in 17/21 (81%) eyes, outer retinal hyporeflective cavitation in 14 (67%) eyes, hyporeflective cavitation at foveal pit in 8 (38%) eyes, and loss of external limiting membrane in 1 (5%) eye. The mean baseline length of the foveal ellipsoid zone loss was 240.17 ± 117.249 µm. The mean baseline central subfield thickness was 155.43 ± 17.215 µm. A total of 8/11 eyes (73%) showed an increase in size of OFD on follow-up. Conclusion: Outer foveal defect in MacTel eyes is characterized predominantly by foveal loss of ellipsoid zone and interdigitation zone with relative preservation of external limiting membrane.