"En face" OCT imaging of the IS/OS junction line in type 2 idiopathic macular telangiectasia

We investigated abnormalities of the photoreceptor inner/outer segment (IS/OS) junction layer viewed "en face" and their functional correlates in type 2 idiopathic macular telangiectasia (type 2 MacTel). Segmentation and "en face" imaging of the IS/OS lines in spectral domain optical coherence tomographic (SD-OCT) volumes were performed manually. Mesopic retinal sensitivity thresholds were determined using a Nidek MP1 microperimeter. "En face" SD-OCT images and microperimetric data were superimposed over images of the fundus. Retinal structure and characteristics of type 2 MacTel were analyzed, and associations of structural changes with function were investigated. We examined 49 eyes of 28 patients (mean age 62.6 ± 9.4 years). Total IS/OS break area ranged from 0.04 to 2.23 mm² (mean 0.63 mm², SD 0.53 mm²) and 0.03 to 1.49 mm² (mean 0.49 mm², SD 0.42 mm²) in right and left eyes, respectively. A correlation between fellow eyes was present (Spearman correlation ρ = 0.770, P < 0.01). An assessment of the repeatability of IS/OS lesion area measurements (n = 19 eyes) revealed an intra-class correlation coefficient of 0.99 (95% confidence interval [CI] of 0.975-0.996). Retinal areas corresponding to an IS/OS break showed a mean retinal sensitivity of 8.3 ± 5.8 and 8.7 ± 5.7 decibels (dB) in right and left eyes, respectively. Mean sensitivity over retinal areas outside the lesion was significantly higher, 17.0 ± 3.3 and 16.7 ± 3.6 dB in right and left eyes, respectively (paired t-test, P < 0.01). Mean aggregate retinal sensitivity loss was 33.5 ± 30.4 dB (n = 40), correlating well with IS/OS lesion area (Pearson correlation coefficient = 0.848, P < 0.01). "En face" OCT imaging of the IS/OS junction layer provides a functionally relevant method for assessing disease severity in type 2 MacTel.