Abstract
Purpose :
Type 2 macular telangiectasia (MacTel) is associated with outer retinal abnormalities and focal sensitivity defects near and at the foveal centre. Optical Coherence Tomographic (OCT) topographic mapping of the IS/OS junction layer is a functionally relevant method for assessing disease severity in MacTel. Our aim was to assess the characteristics and utility of microperimetry and 'en face' OCT imaging data in following disease progression.
Methods :
Patients were selected from an ongoing Phase I open label clinical trial of CNTF in type 2 MacTel. OCT volume scans of an area at least 15°x10° in size with B-scan intervals ≤47µ were acquired using Heidelberg Spectralis (two patients) or CZM Cirrus OCT4000 units (5 patients). Segmentation and topographic mapping of the IS/OS layer was performed manually using a dedicated 3D imaging software (Visage Imaging Amira v5.0). Functional testing was performed using CenterVue Maia devices, using a customized grid. OCT topographic and microperitmetric data maps were superimposed and analyzed in Adobe Photoshop. Aggregate sensitivity loss was calculated as described earlier.
Results :
Fourteen eyes of 7 MacTel patients (ranging in age 48-67 years) were examined at baseline and at 4 subsequent annual follow-up visits. An IS/OS break was apparent in 12 eyes at baseline and in all eyes at 48 months. In 4 eyes of 3 patients however, the break area was consistently too small to be detected by functional testing using the custom grid, in these eyes aggregate loss could not be calculated. Overall, the break area size showed a good correlation with the number of test points <20dB (Spearman's ρ=0.813, p<0.0001, 95%CI 0.710 to 0.881, n=66) as well as with aggregate sensitivity loss (ρ =0.834, P<0.0001, 95%CI 0.716 to 0.906, n=45).
Conclusions :
Overall, we found a good correlation between IS/OS break area size and function loss. OCT mapping of the IS/OS demonstrates structural change before microperimetry can detect a focal loss of retinal sensitivity typical of MacTel. In future studies, the minimum lesion size needs to be determined taking into consideration not only the OCT resolution but also the spacing of the microperimeter test grid and the stimulus size. Calibrating for axial length and refractive power may further improve the precision of lesion area measurements in OCT en face images.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.