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Ferenc B. Sallo, Stela Vujosevic, Ute E. Wolf-Schnurrbusch, Daniel Pauleikhoff, Alan C. Bird, Tunde Peto; Correlation of microperimetry results with 'en face' imaging of the IS/OS junction layer in Type 2 Macular Telangiectasia. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5200.
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Type 2 macular telangiectasia (MacTel) is associated with outer retinal abnormalities at and near the foveal centre. Optical Coherence Tomographic (OCT) signs of these include a break in the line considered to be derived from the IS/OS junctions. Function loss associated with abnormalities of the "IS/OS junction line" has been reported in other diseases but is not known in MacTel. Our aim was to investigate the functional significance of retinal abnormalities in MacTel imaged 'en face' on the level of the IS/OS junctions.
Patients were selected from the MacTel Study, an international prospective study of the natural history, aetiology, pathogenesis and potential therapies of Type 2 MacTel. Standard OCT volume scans containing 128 individual B-scans were acquired using a Topcon 3D OCT-2000 unit. Segmentation and "en face" imaging of the "IS/OS junction line" was performed manually, using dedicated 3D image analysis software. Mesopic retinal sensitivity thresholds were determined using a Nidek MP1 microperimeter at 37 test points with 2 degree intervals within the central 10 degrees of the macula. A sensitivity loss of 5.6 dB or more was considered significant. 'En face' OCT images were superimposed over images of the fundus containing the microperimetric data and adjusted as necessary to attain exact correspondence. Areas corresponding to an abnormality in the IS/OS junction layer were delineated and sensitivity thresholds within these areas were compared to those external to the lesion.
Forty-three eyes of 25 patients with type 2 MacTel (ranging in age 46-77 years, mean 63.7 years, SD=9.8 years) were examined. Retinal areas corresponding to a break in the IS/OS layer showed a mean retinal sensitivity loss of 11.6dB (median=10dB, SD=5.7dB) in right eyes and 11.8dB (median=10dB, SD=5.8dB) in left eyes. Mean sensitivity loss over retinal areas not within the lesion was 3.0dB (median=2dB, SD=3.4dB) in right eyes and 3.0dB (median=2dB, SD=3.2dB) in left eyes. Differences in retinal sensitivity loss between affected and unaffected areas were statistically significant (Mann-Whitney U test, p<0.01 in both right and left eyes).
Areas with a break in the IS/OS layer detectable in en face OCT images are associated with significant local retinal function loss in MacTel. Measuring the size of these areas may offer a means for following disease progression in MacTel.
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