Swept-Source Optical Coherence Tomography and Scan Protocols

The prototype swept-source OCT used in the current study has been previously described and has recently become commercially available (DRI OCT-1; Topcon Corp, Tokyo, Japan). All swept-source OCT examinations were performed by a trained examiner after pupillary dilation. For all patients, horizontal and vertical line scans (12 mm) through the fovea were obtained. For each scan, ∼50 B-scan images were obtained and averaged to reduce speckle noise. The vertical scan was centered on the fovea; the horizontal scan was centered on the midpoint between the fovea and optic disc. 3D imaging datasets were acquired using a raster scan protocol of 512 (horizontal) × 128 (vertical) A-scans per dataset. Each raster scan consisted of 128 B-scans and covered an area of 12 × 8 mm ² or 12 × 9 mm ² , centered on the fovea. In each of the 128 B-scans used for 3D analysis, the RPE line was segmented automatically with manual corrections if necessary to construct 3D images of posterior pole curvature.

Scleral and Choroidal Thickness Measurement Protocol

We measured the choroidal and scleral thicknesses at the center of the fovea and at surrounding parafoveal regions at points 2000 μm superiorly, inferiorly, temporally, and nasally in the multi-averaged OCT scans ( Figure 1 ), with a built-in caliber tool within the software. Retinal thickness was defined as the distance between the vitreoretinal interface and the outer border of the RPE; choroidal thickness was defined as the distance between the outer border of the RPE line and the chorioscleral interface; scleral thickness was defined as the distance between the chorioscleral interface and the outer scleral border. Retinal, choroidal, and scleral thicknesses at the foveal center were calculated as the average of the measurements in the vertical and horizontal OCT images.

Measurement protocol from multi-averaged vertical scans obtained with swept-source optical coherence tomography (OCT) in eyes with dome-shaped macular configuration. Three parameters were measured at the fovea: retinal thickness (blue line), choroidal thickness (black line), and scleral thickness (dashed white double arrow). Choroidal (black line) and scleral (dashed white double arrow) thicknesses were measured at points 2000 μm superior and 2000 μm inferior to the fovea. White arrowheads indicate the outer border of the sclera. Retroocular fat can be seen (white asterisk). In the horizontal scan, choroidal and scleral thicknesses were also measured at 2000 μm temporal and nasal to the fovea. Macular bulge height—the height of the inward bulge of the retinal pigment epithelium (RPE) (yellow double arrow)—was measured above the tangent plane (red dashed line A) at the bottom of the posterior staphyloma in the most convex vertical or horizontal scan. To highlight changes at the bottom of the staphyloma over time, a second line (B) was drawn parallel to line A at the outer surface of the RPE, at the fovea (dashed red line B). The distance between lines A and B is equivalent to macular bulge height. White arrow shows the direction of the OCT scan.

We measured the macular bulge height as the height of the inward bulge of the RPE above a presumed line tangent to the RPE (dashed red line A) at the fovea within the bottom of the posterior staphyloma in the most convex vertical or horizontal scans ( Figure 1 ). Macular bulge height depends mainly on 2 parameters. One is the difference between scleral and choroidal thicknesses at the fovea and parafoveal regions, and the second is the change in depth of ocular concavities within the staphyloma. To highlight these dynamic changes at the bottom of the staphyloma, a second line (B) was drawn parallel to the line (A) tangent to the outer surface of the RPE at the fovea (dashed red line B, Figures 1–4 and Supplemental Figure , available at AJO.com ). The distance between lines A and B is equivalent to the macular bulge height.

Longitudinal increases in macular bulge height and deepening of the ocular concavities over time in eyes with a dome-shaped macular configuration. Left eye with high myopia in a 43-year-old man (decimal visual acuity = 0.1 [Snellen: 20/200], axial length = 29.70 mm, and refractive error = −15.50 diopters). (Top, left) Fundus photograph showing a tessellated fundus with diffuse atrophic changes of the retinal pigment epithelium (RPE) and a posterior staphyloma. (Middle and Bottom, left) RPE atrophic changes become more diffuse over time, particularly at the edge of the posterior staphyloma (yellow arrowheads). (Top, right) A vertical-scan swept-source optical coherence tomography (OCT) image shows dome-shaped macular configuration (macular bulge height = 262 μm). (Middle, right) Macular bulge height has increased to 304 μm. Analysis of the OCT images shows 2 outward concavities within the staphyloma have increased in depth under the dashed red line (B) as compared to the initial examination. Inner scleral contour is steeper with more posterior bowing (block white arrows). (Bottom, right) At the end of the follow-up period, macular bulge height has increased to 326 μm and ocular concavities appear deeper with steepened contour. White arrows show the direction of the OCT scan.

Asymmetric scleral thinning at the macular region in dome-shaped macular configuration. Right eye of a 41-year-old man with high myopia (decimal visual acuity = 0.5 [Snellen: 20/40], axial length = 29.2 mm, and refractive error = −15.70 diopters). (Left column) At the initial examination. (Right column) At the end of the follow-up period. (Top, left) Fundus photograph showing a tessellated fundus with diffuse retinal pigment epithelium (RPE) atrophic changes and a scleral thickness map of the right eye. Scleral thickness was measured at the foveal center and 4 parafoveal locations at 2000 μm from the foveal center (C = center; S = superior, I = inferior, T = temporal, N = nasal). (Middle, left) A vertical-scan swept-source optical coherence tomography (OCT) image shows dome-shaped macular configuration. The sclera is relatively thicker at the fovea as compared to the areas of outward concavities superiorly and inferiorly (white arrowheads). Macular bulge height was 255 μm. (Bottom, left) Horizontal OCT scan shows an almost flat contour of the RPE. The sclera appears thicker at the fovea as compared to parafoveal measurement points at 2000 μm nasally and temporally (white arrowheads). (Top, right) A fundus photograph taken at the end of the follow-up period shows that the RPE atrophic changes have become more diffuse (yellow arrowheads). Scleral thickness map shows scleral thinning at the 5 locations studied. (Middle, right) A follow-up vertical OCT scan shows increased macular bulge height (281 μm) and scleral thinning at parafoveal locations 2000 μm superiorly and inferiorly. By analysis of the OCT images, the dashed red line (B) is seen to traverse the bottom of the staphyloma at higher level. (Bottom, right) A follow-up horizontal OCT scan shows scleral thinning at the parafoveal locations 2000 μm temporally and nasally, as compared to the initial scan. The scleral thinning is seen more clearly on the temporal side (white arrowheads). White arrows show the direction of the OCT scan.

Longitudinal changes in scleral thickness and macular bulge height in dome-shaped macular configuration. Right eye of a 63-year-old woman with high myopia (decimal visual acuity = 0.40 [Snellen: 20/50], axial length = 30.14 mm, refractive error = −17.50 diopters). (Upper row) Fundus photograph and scleral thickness map at the initial examination (C = center, S= superior, I = inferior, T = temporal, N = nasal). Vertical-scan swept-source optical coherence tomography (OCT) image shows a dome-shaped macular configuration. Measured macular bulge height (yellow double arrow) was 151 μm. (Bottom row) At the end of follow up. Fundus photograph shows progression of the atrophic changes. Scleral thickness map shows scleral thinning at the 5 measured locations as compared to the initial examination. A follow-up vertical OCT scan shows scleral thinning at the area of outward concavities (white arrowheads). Despite the overall scleral thinning, macular bulge has increased to 171 μm. By analysis of the OCT images, the 2 outward concavities are seen to be deeper within the staphyloma under the dashed red (B) line (white block arrows). White arrows show the direction of the OCT scan.

The outer scleral border was carefully identified in the OCT scans from retro-ocular structures such as the Tenon capsule, episcleral tissue, inferior oblique aponeurosis, and orbital fat. Scleral tissues were identified by their lamellar morphology, the continuity of the outer surface of the sclera within the raster lines in the vertical and horizontal scans, and high reflectivity values.

In the follow-up examinations, the choroidal and scleral thicknesses were measured again with careful attention to measure at the exact location from the initial visit. In 6 eyes, the outer border of the sclera was not clearly visible at the fovea, either at the first visit or at follow-up, which precluded comparison. These eyes were excluded from the study. In all recruited subjects, the outer border of the sclera at the fovea and at the 4 parafoveal locations was identified clearly at the initial and follow-up visits.

Statistical Analysis

Statistical analysis was performed using SPSS statistical software (version 20; SPSS Inc, Chicago, Illinois, USA). All values are expressed as mean ± standard deviation. The measured visual acuity was converted to the logarithm of the minimal angle of resolution (logMAR) for statistical analysis. The paired t test was used to compare numerical variable means for baseline and follow-up measurements. Choroidal and scleral thicknesses at various parafoveal regions were compared to that of the foveal center using 1-way analysis of variance with least significant difference post hoc analysis. A P value of less than .05 was considered to be statistically significant.