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

Abstract

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 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).

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

Figure 1

The IS/OS lesion in OCT “en face” and corresponding B-scan images. (A) Representative B-scan of a type 2 MacTel eye, from a 6 × 6 mm volume consisting of 128 B-scans. (B) The en face image of the full scan area on the level of the IS/OS line, showing the shadowgram of the retinal blood vessels. The dark area toward the center of the image corresponds to the outer retinal “empty space” seen in (A), the dark grey area around it is the IS/OS break. Horizontal dark stripes are due to minor axial misalignments between the individual B-scans. (C, D, E, F) Illustrate the pathologic “collapsing layers” extending between the inner and outer retina. Orange horizontal lines mark the position of respective B-scan within the corresponding en face image.

Figure 2

Functional correlates of the IS/OS break. Left column: RF fundus image. Middle column: RF with the “en face” OCT image superimposed. Right column: MP1 mesopic retinal sensitivity maps superimposed. Significantly higher thresholds were measured over areas with an IS/OS break, the highest loss co-localizing with the “collapsing layers.” (B, C) Segments of a ring with lower reflectance encircling the central IS/OS break area apparent. In many cases a corresponding pattern is discernible in infrared images of the fundus.

Figure 3

(A) IS/OS break area (pixels) in fellow eyes (x-axis, left eyes; y-axis right eyes; Spearman correlation ρ = 0.770, P < 0.01). (B) Correlation between IS/OS break area in pixels (x-axis) and aggregate retinal sensitivity loss (dB). Pearson correlation coefficient = 0.848, P < 0.01.

Figure 4

In some “en face” images, a highly reflective ring around the central lesion was seen. A similar pattern was not apparent outside the IS/OS layer within the OCT volume or in other imaging modalities (columns [B] FFA and [C] FAF), except in the confocal blue light reflectance image (D) and partially in the infrared (A).