Progressive inner retinal neurodegeneration in non-proliferative macular telangiectasia type 2

Abstract

Purpose: Patients with non-proliferative macular telangiectasia type 2 (MacTel) have ganglion cell layer (GCL) and nerve fibre layer (NFL) loss, but it is unclear whether the thinning is progressive. We quantified the change in retinal layer thickness over time in MacTel with and without diabetes.

Methods: In this retrospective, multicentre, comparative case series, subjects with MacTel with at least two optical coherence tomographic (OCT) scans separated by >9 months OCTs were segmented using the Iowa Reference Algorithms. Mean NFL and GCL thickness was computed across the total area of the early treatment diabetic retinopathy study grid and for the inner temporal region to determine the rate of thinning over time. Mixed effects models were fit to each layer and region to determine retinal thinning for each sublayer over time.

Results: 115 patients with MacTel were included; 57 patients (50%) had diabetes and 21 (18%) had a history of carbonic anhydrase inhibitor (CAI) treatment. MacTel patients with and without diabetes had similar rates of thinning. In patients without diabetes and untreated with CAIs, the temporal parafoveal NFL thinned at a rate of -0.25±0.09 µm/year (95% CI [-0.42 to -0.09]; p=0.003). The GCL in subfield 4 thinned faster in the eyes treated with CAI (-1.23±0.21 µm/year; 95% CI [-1.64 to -0.82]) than in untreated eyes (-0.19±0.16; 95% CI [-0.50, 0.11]; p<0.001), an effect also seen for the inner nuclear layer. Progressive outer retinal thinning was observed.

Conclusions: Patients with MacTel sustain progressive inner retinal neurodegeneration similar to those with diabetes without diabetic retinopathy. Further research is needed to understand the consequences of retinal thinning in MacTel.

Keywords: Degeneration; Imaging; Macula; Retina.

Figure 1. Regions of interest. Average thickness for NFL, GCL layers, INL, IPL and outer retina was computed within subfield 4 of the ETDRS grid (orange) and for the entire 6 mm diameter ETDRS circle (purple). Regions are aligned to an eye with MacTel in this Heidelberg Spectralis SLO image. MacTel, macular telangiectasia type 2; GCL, ganglion cell layer; NFL, nerve fibre layer; ETDRS, early treatment diabetic retinopathy study; IPL, inner plexiform layer; INL, inner nuclear layer; SLO, scanning laser ophthalmoscopy.

Figure 2. Fitted rates of inner retinal thickness over time for all samples in 10 regions (A, nerve fibre layer (NFL) in ETDRS subfield 4; B, NFL of entire grid; C, ganglion cell layer (GCL) in ETDRS subfield 4; D, GCL of entire ETDRS grid; E, inner plexiform layer (IPL) in ETDRS subfield 4; F, IPL of entire grid; G, inner nuclear layer (INL) in ETDRS subfield 4; H, INL of entire grid; I, outer retina in ETDRS subfield 4; J, outer retina of entire grid). Each point represents thickness for each optical coherence tomographic (OCT) (ie, each scan per each visit) and each line represents the model fit for each eye which demonstrates a trend towards gradual thinning over time in these subgroups and layers. ETDRS, early treatment diabetic retinopathy study.