Three-dimensional characteristics of outer retinal atrophy in type 2 idiopathic macular telangiectasia.

Abstract

 

Purpose

 

Type 2 macular telangiectasia (MacTel) is associated with outer retinal abnormalities at and near the foveal centre. Optical Coherence Tomographic (OCT) topographic mapping of the IS/OS junction layer (or ellipsoid zone, EZ) is a functionally relevant method for assessing disease severity in MacTel. On OCT, the photoreceptor outer segment tips (POST line or interdigitation zone, IZ) are also associated with a clear signal. Our aim was to examine the characteristics of outer retinal atrophy in in MacTel, in 3 dimensions.

 

Methods

 

Patients were selected from the MacTel Study cohort. OCT volume scans of an area 15°x10° in size with 11µ B-scan intervals were acquired using Heidelberg Spectralis OCT units. Automated segmentation and topographic mapping of the POST (IZ) and IS/OS (EZ) layers was reviewed and corrected manually. OCT topographic maps were superimposed and compared in 3D using a dedicated 3D imaging software.

 

Results

 

Eighteen eyes of 10 MacTel patients (ranging in age 34-68 years, mean age 53.2, SD=13.7 years) were examined. In 13 eyes a break was apparent in both the IS/OS (EZ) and the POST (IZ). Consistently, the POST (IZ) break appeared larger than the break in the IS/OS (EZ). In 11 cases, the IS/OS (EZ) deviated through the POST (IZ) break towards the retinal pigment epithelium (RPE). In 5 eyes no IS/OS (EZ) break was apparent. In 3 of these however, a POST (IZ) break was detectable and the shape of the IS/OS (EZ) at the temporal part of the fovea externa was deformed, deviating towards the RPE.

 

Conclusions

 

A break in the POST (IZ) layer and deviations in the shape of the IS/OS (EZ) may precede a full break in the IS/OS (EZ). This may be interpreted as a shortening of the photoreceptor outer segments before degenerative changes appear in the junctions or the inner segments. A 3D topographic analysis of the outer retina may adjunct current methods and provide a more accurate tool for characterizing early disease as well as clues to the sequence of cellular degeneration in MacTel.