Purpose.: 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).

Methods.: 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.

Results.: 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 mm 2 (mean 0.63 mm 2, SD 0.53 mm 2) and 0.03 to 1.49 mm 2 (mean 0.49 mm 2, SD 0.42 mm 2) 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).

Conclusions.:“En face” OCT imaging of the IS/OS junction layer provides a functionally relevant method for assessing disease severity in type 2 MacTel.