All procedures in this study adhered to the tenets of the Declaration of Helsinki and were approved by the investigational review board of Central Ethic Committee IRCCS Lazio. All subjects gave their informed consent after the aim of the study had been fully explained.
Thirty-nine FEs of 39 consecutive patients (17 men and 22 women; mean age = 71.18 ± 10.91 years) with unilateral IERM were enrolled. Thirty eyes of 30 age- and sex-matched healthy subjects with no ocular disease were recruited as controls (14 men and 16 women; mean age = 68.33 ± 12.45 years,
P = 0.315 vs. FEs group). Only one eye randomly selected was enrolled for inclusion in the control group. Before imaging, all patients underwent ophthalmic examination, including best-corrected visual acuity and fundus examination, performed by a retina specialist using a 90 diopter (D) indirect lens. Inclusion criteria were the presence of IERM in only one eye, associated with absence of any alteration detectable with SD-OCT in the FE. Exclusion criteria were the presence of any retinal or choroidal disease, such as retinal detachment, retino-vascular disease, AMD, diabetic retinopathy, glaucoma or ocular hypertension, a history of ocular laser or surgery, eyes with refractive errors >±3 D, media opacities that prevented good visualization of the fundus, any associated systematic disorders (e.g. systemic corticosteroids intake, diabetes, or hypertension), or vascular diseases without retinopathy, which would affect the VD independent of a FE ERM. SD-OCT imaging exclusion criteria for unaffected FEs were: no changes of the normal foveal profile, flat surface of the analyzed area, and no changes in all the macular layers, including RPE. Mean demographic data and clinical characteristics of patient and CEs are shown in
Table 1.
The macula in both FEs and CEs groups was assessed using the SD-OCT (Cirrus 5000; Carl Zeiss Meditec, Inc., Dublin, CA, USA). The device performed each acquisition at a speed of 100 kHz, 68.000 A-scans per second, using an 840-nm superluminescent diode; the macula was analyzed by SD-OCT using the 512 × 128 scan pattern in which a 6 × 6 mm area centered on the fixation point is scanned with 128 B-scan composed by 512 A-scan. The software (version 6.5.0.772) computed the mean macular thickness in the 6 × 6 mm area using a whole Early Treatment Diabetic Retinopathy Study (ETDRS) grid centered on the fixation point, which contains 3 concentric rings of diameters 1, 3, and 6 mm, and 2 reticules to divide the macula into 9 subfields, in each the retinal thickness is separately measured (central: C1; inner ring: S3, N3, I3, and T3 [parafovea]; outer ring: S6, N6, I6, and T6 [perifovea]
20;
Fig. 2A).
Using the same 6 × 6 cube scan, the algorithm performed the segmentation of mean thickness of the whole perifoveal GCL, within a 14.13 mm
2 elliptical annulus area (dimensions: a vertical inner and outer diameter of 0.5 and 2.0 mm and a horizontal inner and outer diameter of 0.6 and 2.4 mm, respectively) centered on the fovea (
Fig. 2B). The size of the inner ring in the annulus was chosen to exclude the foveal area, where the GCL is too thin to be detected; the size and shape of the outer ring was selected because it conforms closely to the real anatomy of the normal retinal ganglion cells distribution in the macular region.
The algorithm identifies the outer boundary of the nerve fiber layer (NFL) and the outer boundary of the inner plexiform layer (IPL), so that the difference between the NFL and the IPL outer boundary segmentations yields the GCL.
21 The following GCL thickness measurements were analyzed: mean and sectorial: superior (S); superonasal (SN); inferonasal (IN); inferior (I); inferotemporal (IT); and superotemporal (ST; see
Fig. 2B).
Images with visible eye motion or blinking artefacts and with poor image quality were excluded (defined as signal strength lower than 5/10).
In a subgroup of 25 patients (14 women and 11 men), and 25 controls (13 women and 12 men), the macula was assessed using the split-spectrum amplitude-decorrelation angiography with PLEX Elite 9000 (version 1.5.0.15909; Carl Zeiss Meditec Inc.). It is a swept-source OCT angiography (SS-OCT-A) that provides automated segmented enface OCT of different plexus: SCP, DCP, avascular retina, choriocapillaris (CC), and choroid (Ch). OCT-A on the PLEX Elite 9000 is generated with the OMAG algorithm (optical microangiography),
22,23 which utilizes the complete complex OCT data signal, including both amplitude and phase, to detect motion of red blood cells within sequential OCT B-scans performed repeatedly at the same location.
23–25 The device performed each acquisition at a speed of 100,000 A-scans per second, using as optical source a swept source tunable laser, center wavelength between 1040 and 1060 nm; axial resolution 6.3 µm, and transverse resolution 20 µm. A 6 × 6 mm cube scan was performed, 500 A-scan made up a B-scan, 500 horizontal B-scan were sampled in the scanning area to form a 6 × 6 mm 3-dimensional data cube.
Images with visible eye motion or blinking artifacts and with poor image quality were excluded (defined as signal strength lower than 7/10). OCTs were visually assessed by the same retina specialist (author A.M.C.) to ensure proper segmentation of the GCL and the SCP and DCP.
The software, using an algorithm that is a prototype provided by the manufacturer (ARI Network - Zeiss), computed the VD in the 6 × 6 mm area using the ETDRS grid centered on the fixation point, which contains 3 concentric rings of diameters 1, 3, and 6 mm, and 2 reticules to divide the macula into 9 subfields, analogous to the previous described ETDRS grid (central = C1; inner ring = S3, N3, I3, and T3; and outer ring = S6, N6, I6, and T6). As the elliptical annulus area in which the thickness of GCL is computed is not homologous to the ETDRS grid, we chose to compare the VD of more than one perfusion area in FEs and CEs, according to the concept that the analyzed area had to overlap with the elliptical annulus area; therefore, the areas studied were: inner ring (sectors S3, N3, I3, and T3), outer ring (sectors S6, N6, I6, and T6), and 6 mm mean (sectors C1, S3, N3, I3, T3, S6, N6, I6, and T6; see
Fig. 2A). Data are expressed as percentage VD.
The statistical analyses used SPSS software version 15.0 (SPSS, Inc., Chicago, IL, USA). The data obtained were analyzed with frequency and descriptive statistics. Data collected underwent 1-way ANOVA. A level of P < 0.05 was accepted as statistically significant.