shows the pit volume results for control subject 3. In general, the pit depth and volume measurements from both eyes of the same subject were similar. Control subject 3 had the largest right–left difference, with the exception of ROP subject 7 who had a dragged macula in the right eye (). The average difference between the two methods of pit area measurement for the rasters shown in was 5.4%. A slight asymmetry (pit width/pit height ≈ 1.1) was found in both control and ROP subjects, but this is accounted for in both measurement methods.
Figure 5 Pit volume data for control subject 3 comparing raster and radial scans, raster area calculation methods, and left and right eyes. Squares: left eye data; diamonds: right eye data. Filled symbols: calculation method that uses the particle-bounding box; (more ...)
shows composite images of one eye of all subjects. The foveal pit is present although quite shallow in the ROP subjects. Vessels were identified overlying the fovea in all ROP subjects except subject 9. In the control subjects, the inner retinal layers (NFL, GCL, inner plexiform layer [IPL], inner nuclear layer [INL], and OPL) at 500 to 750 μm eccentricity were identifiable. With decreasing eccentricity, these inner layers tapered and were absent in the central 100 to 200 μm of the fovea. In contrast, all inner retinal layers were present and contiguous across the central fovea in the ROP subjects, except subject 9. In both control and ROP subjects, the ONL thickness increased in the fovea. The thickness of photoreceptor inner (ELM-CC) and outer (CC-RPE) segment layers was similar in ROP and control subjects.
Figure 6 Montage of cross-sectional composite images from one eye of all subjects. (a–e) Control subjects; (f–j) subjects with ROP. Composite images were created from 4 to 11 frames. Scan length is 1455 μm except for those in (e) and ( (more ...)
Retinal layer thickness is quantified in . The measurements include all except subject 7, whose right eye, which had high myopia and a dragged macula, and subject 9, whose left eye was not imaged. Although individual retinal layers of the right eye of subject 7 could not be resolved, we estimated the full retinal thickness from cross-sectional scans to be ~522 μm, which exceeded that in any other subject with ROP.
Figure 7 Thickness measurements (mean ± SE) of retinal layers at several eccentricities in ROP (8 eyes, all except subjects 7, OD, and 9, OS) and control subjects (10 eyes). Top: layers measured in (a–d). (a) Full retinal thickness from ILM to (more ...)
The full retinal thickness was greater in subjects with ROP than in control subjects at all eccentricities (). The difference was greatest in the fovea where the full retinal thickness was 47% higher in subjects with ROP (279.0 μm vs. 190.2 μm) and the difference decreased to 17% at 437 μm eccentricity (302.0 μm vs. 257.6 μm; average of −437 and +437 μm). In the subjects with ROP, the total retinal thickness did not vary significantly with eccentricity (P = 0.65), further indicating a shallow pit. The inner retinal layers were also significantly thicker in the subjects with ROP (), and the difference varied little with eccentricity. The difference between ROP and control for the total thickness () and inner retinal thickness () was significant (P < 10−8). The thickness of the inner retinal layers in subjects with ROP is slightly greater nasally than temporally (P = 0.013 at 437 μm). The difference in ONL thickness () between ROP and control subjects was greatest at the fovea (31.5 μm, P < 0.00005) and negligible for eccentricities ≥250 μm. There was very little difference (<4 μm, P = 0.184) found in the photo-receptor layer thickness between ROP and control subjects (). For the control subjects, the photoreceptor layer increased from 62 μm at 437 μm eccentricity to 75 μm in the fovea.
The pit depth for ROP and control subjects is shown in . The foveal pit depth was measured from the 3-D maps and cross-sectional images and defined as the distance from the bright reflex at the base of the pit to the arbitrarily chosen point where the pit reaches a radius of 728 μm. The pit depth is smaller by more than a factor of two in ROP subjects.
The results of the pit volume measurement are shown in . Pit area as a function of depth extracted from raster and lines scans of five control (10 eyes) and five ROP (8 eyes) subjects is plotted. If volumetric raster scans were corrupted by eye movements (), line scans were used and radially isotropic pits were assumed. The second-order polynomial fit and equation are also shown on the graph. The foveal pit in ROP subjects was wider and shallower than that in the control subjects, except for ROP subject 9.
Figure 8 Pit area as a function of depth measured from the base of the pit for ROP (8 eyes) and control subjects (10 eyes). Equation for second-order polynomial fit (with intercept set to 0) and correlation coefficient is shown for each data set. Fit for ROP subjects (more ...)
En face images () compare the vasculature in two distinct layers (IPL and OPL) from an ROP and a control subject. In the ROP subject, vessels overlay the entire foveal region (). The capillaries that surrounded the AZ were not clearly resolved in the control subject, although a vessel within 250 μm of the fovea center that may be part of the ring is indicated by an arrow in . The average diameter of 10 vessels in the OPL for the subject with ROP and the control subject is compared in . The average FWHM diameter of the capillaries was 35% lower in the subject with ROP.
Figure 9 Retinal vasculature in control subject 3 and ROP subject 8. (a–d) Control and (e–h) ROP subjects. En face views (a, c, e, g) were created by averaging the axial slices shown between the horizontal lines in the corresponding cross-sectional (more ...)
Figure 10 OPL vessel diameter measurement in (a) control subject 3 and (b) ROP subject 8 (from the same en face images as shown in ). Ten vessels were randomly chosen and their cross-sectional profiles measured, aligned, and averaged. The profile locations (more ...)