Characterization of Choroidal Layers in Normal Eyes with En Face Swept-Source Optical Coherence Tomography

Abstract

Purpose: To characterize anatomic features of the choroid in normal eyes using en face images from a long wavelength swept-source optical coherence tomography (SS-OCT) prototype.

Methods: Normal subjects were prospectively examined with a SS-OCT system (1050nm, 100,000 A-lines/sec, 6µm axial resolution). Multiple 3D 12x12mm macular scans were processed with a motion correction algorithm and merged to increase signal. Segmentation of the retinal pigment epithelium (RPE) generated a reference surface and en face SS-OCT images were extracted at varying depths every 4 µm (1pixel) from the RPE/Bruch’s membrane to the sclera. Qualitative and quantitative features on en face images were characterized by systematic analysis of the choroidal vessels. Enrolled subjects were divided into two age-groups: <50 years and ≥50 years.

Results: Thirty eyes from 22 normal subjects were enrolled; 10 males; mean age 39.9 years (range 23 to 88); mean BCVA 20/20 (range 20/15 to 20/25). En face SS-OCT images at the level of the RPE, choriocapillaris (CC), inner choroid (IC), outer choroid (OC), and choroidal-scleral interface showed specific features that permitted the identification of each layer and transition zones between them. In the younger group (<50 years) the mean thickness of each choroidal layer was: CC 69.8µm (SD ±21.8µm), IC 58.9µm (SD ±16.8µm), and OC 193.6µm (SD ±52.9µm). In the older group (≥50 years) the mean thickness was: CC 49µm (SD ±14.6µm), IC 49µm (SD ±22.8µm), and OC 161.3µm (SD ±64.2µm). In the younger group, the mean proportion of each layer of the total choroidal thickness was: CC 21.9% (SD ±6.1%), IC 18.5% (SD ±4.8%), and OC 59.6% (SD ±7.2%). In the older group, the mean proportion was: CC 20.9% (SD ±7.1%), IC 17.8% (SD ±4.7%), and OC 61.3% (SD ±5.5%). There was no significant difference in the proportions between the two groups (p=0.16, p=0.56, and p=0.41 respectively).

Conclusions: En face SS-OCT at 1050nm enables qualitative and quantitative characterization of the choroid in normal eyes, which is not readily appreciated on cross-sectional OCT. In our series, choroidal layers were thinner in the older group, but the proportion of thickness between the layers remained constant in both groups. In vivo evaluation of the choroid at variable depths may lead to pathophysiological inferences and is potentially valuable in the diagnosis and management of age related posterior segment disease.

Keywords: 452 choroid • 550 imaging/image analysis: clinical • 413 aging