July 2012
Volume 53, Issue 8
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Glaucoma  |   July 2012
The Effects of Peripapillary Atrophy on the Diagnostic Ability of Stratus and Cirrus OCT in the Analysis of Optic Nerve Head Parameters and Disc Size
Author Notes
  • From the Department of Ophthalmology and Visual Science, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea. 
  • Corresponding author: Chan Kee Park, Department of Ophthalmology and Visual Science, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea, 505 Banpo-dong, Seocho-ku, Seoul 137-701, Korea; ckpark@catholic.ac.kr
Investigative Ophthalmology & Visual Science July 2012, Vol.53, 4475-4484. doi:10.1167/iovs.12-9682
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      Sun Young Kim, Hae-Young L. Park, Chan Kee Park; The Effects of Peripapillary Atrophy on the Diagnostic Ability of Stratus and Cirrus OCT in the Analysis of Optic Nerve Head Parameters and Disc Size. Invest. Ophthalmol. Vis. Sci. 2012;53(8):4475-4484. doi: 10.1167/iovs.12-9682.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose.: We compared the diagnostic ability of Stratus and Cirrus optical coherence tomography (OCT) in optic nerve head (ONH) analysis, and examined the effects of optic disc size and peripapillary atrophy (PPA) on their diagnostic capacity.

Methods.: Stratus and Cirrus OCT was performed in 28 control and 78 glaucomatous eyes. ONH parameters and diagnostic capacity calculated from the area under the receiver operating characteristics curve (AUC) were compared between the two modalities. Glaucomatous eyes were classified by optic disc size and the presence/absence of PPA, and their AUCs were compared.

Results.: Rim area (AUC 0.936) and rim volume (AUC 0.824) showed the best diagnostic capacity in Cirrus and Stratus OCT, respectively. Cirrus OCT showed greater diagnostic ability over Stratus OCT for all ONH parameters. With increasing ONH size, diagnostic ability declined in rim and disc areas, while it improved in average cup-to-disc ratio (CDR), vertical CDR, and cup volume for both modalities. Optic disc size as measured by Stratus OCT was significantly larger than that by Cirrus OCT in glaucomatous eyes with PPA. In addition, the diagnostic capacity of all ONH parameters declined significantly for glaucomatous eyes with PPA, especially for Stratus OCT. In Cirrus OCT, retinal nerve fiber layer (RNFL) thickness showed poorer diagnostic ability than rim area in the glaucoma with PPA group.

Conclusions.: The diagnostic capacity of Cirrus OCT was superior to that of Stratus OCT. Considering the principle of determining the disc margin, as Stratus OCT tends to make excessive measurements of the optic disc in PPA, caution is required in analyzing the results.

Introduction
There is an increasing trend away from diagnosing the “eye of the patient” through the “eye of the doctor.” Traditional diagnostic imaging tools are being replaced by new imaging tools that are removing much of the uncertainty in diagnosis. Clinical assessment of the optic disc by a trained physician is highly subjective and time-consuming. Fundus photography also shows a low-to-medium degree of interobserver agreement and suffers from the inability to detect diffuse RNFL loss. 13 Standard automated perimetry can detect visual field loss only after a substantial loss of retinal ganglion cell (RGC) axons. 4,5 Various computerized imaging modalities recently have been developed to overcome these limitations, providing objective and reproducible quantitative measurements of retinal nerve fiber layer (RNFL) thickness and optic nerve head (ONH) anatomy. Therefore, the diagnosis of pre-perimetric glaucoma, which is identifiable as optic disc abnormalities with no visual field loss, may be aided by the use of these newer modalities, including optical coherence tomography (OCT) and Heidelberg retina topography (HRT). 
Evaluation of the optic disc is fundamental for the diagnosis and management of glaucoma. The ONH and lamina cribrosa have long been implicated as critical sites in the initiation of glaucoma. 69 Previous studies using Stratus OCT indicated increased sensitivity in detecting glaucoma and its progression after combining data regarding RNFL thickness and ONH measurements. 10 The assessment of thin RNFL thickness, which has been suggested to be an early sign of glaucomatous damage, may be challenging in patients with myopia and severe peripapillary atrophy (PPA). 11 We predict that, if precise measurements could be obtained, the neuro-retinal rim area and cup-to-disc ratio (CDR) of the ONH would be more meaningful in such patients rather than RNFL thickness. Moreover, ONH parameters have been reported to have an important role in other diseases, including Leber's hereditary optic neuropathy and dominant optic atrophy. 1216 Despite being a good predictor of glaucoma, clinical evaluation of the ONH is subject to interobserver variation, although agreement can be substantial given the appropriate conditions. This sometimes is an extremely difficult task for non-experts. To justify reproducibility and accuracy, one must raise a problem with inaccuracy of evaluating discs by a clinician. 
New high-definition (HD)-OCT recently has become available. ONH parameters may be easier to determine by high-resolution spectral-domain (SD)-OCT, given the high contrast between the nonreflective vitreous and inner limiting membrane, and the ability of SD-OCT to delineate the end of Bruch's membrane, thereby defining a stable reference plane from which to measure the neuroretinal rim, while the Stratus OCT algorithm defines the disc margin as the end of the RPE/choriocapillaris layer, and uses a default reference plane located 150 μm above the RPE to define the cup margin (Fig. 1). For this reason, ONH parameters by Stratus OCT tend to be influenced by disc size. 17 Thus, ONH measurements obtained by SD-OCT may prove to be more accurate and more reproducible in evaluating patients with glaucoma. To our knowledge, there has been only one previous study, 18 though this did not regard the presence/absence of PPA, to compare the ability of ONH parameters measured using the database between Cirrus HD-OCT (Carl Zeiss Meditec Inc., Oberkochen, Germany) and Stratus OCT, and reports regarding Stratus OCT ONH analysis in glaucoma have been fewer than reports regarding RNFL thickness. 19 The study was done on normal and glaucomatous eyes, classified according to disc size and the presence/absence of PPA. To our knowledge, this is the first study to compare the diagnostic abilities of Cirrus and Stratus OCT for ONH parameters concerning PPA. 
Figure 1. 
 
Images of identical ONHs by Heidelberg SL-OCT (top), TD-OCT (middle), and SD-OCT (bottom). The Heidelberg SL-OCT used as a landmark for ONH morphometry enables detailed imaging of the ONH, displaying not only the RPE but also Bruch's membrane. Yellow arrows: The border of Bruch's membrane, which is the actual disc margin. Red arrows: The border of the RPE, which is defined as the PPA margin. As Stratus OCT (middle image) determined the disc margin by the RPE, it misidentified areas devoid of RPE as disc area and marked the disc including the PPA area (light blue straight line). The cup was calculated arbitrarily as the area where the parallel line 150 μm above the light blue line (red straight line) and the inner margin (light blue curved line) meet. In contrast, Cirrus OCT, which produced fewer artifacts, was better able to visualize Bruch's membrane and, therefore, described the disc margin precisely (black dots). As the cup margin was determined according to the direct measurement of retinal nerve fibers, it was not parallel to the disc margin and was more accurate.
Figure 1. 
 
Images of identical ONHs by Heidelberg SL-OCT (top), TD-OCT (middle), and SD-OCT (bottom). The Heidelberg SL-OCT used as a landmark for ONH morphometry enables detailed imaging of the ONH, displaying not only the RPE but also Bruch's membrane. Yellow arrows: The border of Bruch's membrane, which is the actual disc margin. Red arrows: The border of the RPE, which is defined as the PPA margin. As Stratus OCT (middle image) determined the disc margin by the RPE, it misidentified areas devoid of RPE as disc area and marked the disc including the PPA area (light blue straight line). The cup was calculated arbitrarily as the area where the parallel line 150 μm above the light blue line (red straight line) and the inner margin (light blue curved line) meet. In contrast, Cirrus OCT, which produced fewer artifacts, was better able to visualize Bruch's membrane and, therefore, described the disc margin precisely (black dots). As the cup margin was determined according to the direct measurement of retinal nerve fibers, it was not parallel to the disc margin and was more accurate.
Methods
Subjects
All patients were recruited in a consecutive manner from the glaucoma clinic of the Department of Ophthalmology, Seoul St. Mary's Hospital, The Catholic University of Korea, Seoul, Korea from February 2009 through July 2010. Each subject underwent a complete ophthalmologic examination, including visual acuity, refraction, slit-lamp biomicroscopy, gonioscopy, Goldmann applanation tonometry, dilated stereoscopic examination of the optic disc, red-free fundus photography, Stratus time-domain (TD)-OCT, Cirrus HD-OCT, HRT (Heidelberg Engineering GmbH, Heidelberg, Germany), and Humphrey visual field (VF) examination using the Swedish Interactive Threshold Algorithm Standard 24-2 test (Carl Zeiss Meditec). All examinations for each subject were performed on the same day. 
For inclusion in the study, subjects had to meet the following criteria: best-corrected visual acuity of 20/40 or better, refractive spherical error within the range of −6.00 to +3.00 diopters (D) or a cylinder within the range of ± 2.50 D, presence of a normal anterior chamber and open-angle on slit-lamp and gonioscopic examinations, and reliable VF test results with a false-positive error <15%, false-negative effort <15%, and fixation loss <20%. Subjects were excluded on the basis of any of the following criteria: a history of any retinal disease, including diabetic or hypertensive retinopathy; a history of eye trauma or surgery, with the exception of uncomplicated cataract surgery; other optic nerve disease except glaucoma, and a history of systemic or neurologic diseases that may affect the VF. One eye was selected randomly if both eyes were found to be eligible. Subjects who fulfilled the following criteria were classified as having glaucoma: glaucomatous VF loss (defined as those with a cluster of 3 points with probabilities of <5% on the pattern standard deviation [PSD] map in at least 1%; or a cluster of 2 points with a probability of <1%, and a glaucoma hemifield test result outside normal limits; or a PSD outside 95% of normal limits in at least two reliable VF examinations), and glaucomatous ONH changes, including diffuse or localized rim thinning, disc hemorrhage, a notch in the rim, and a vertical CDR higher than that of the other eye by more than 0.2. Subjects with a normal RNFL configuration according to red-free photography, an absence of ONH abnormalities as defined for glaucoma, an IOP ≤21 mmHg, and normal VF results were assigned to the normal control group. 
The study was approved by our institutional review board and conformed to the Declaration of Helsinki. Informed consent was obtained from all subjects. 
The ONH parameter was measured using Stratus and Cirrus OCT in 28 control and 78 glaucomatous eyes. The demographic and clinical characteristics of the healthy subjects, subjects with glaucoma, and three subgroups of glaucomatous patients according to disc size are shown in Table 1. The mean age (53.48  ±  10.74 in controls vs. 55.72  ±  11.23 in glaucoma patients, P = 0.421), male-to-female ratio (17:11 in controls vs. 40:38 in glaucoma patients, P = 0.712), central corneal thickness (P = 0.552), spherical equivalent (P = 0.671), and axial length (P = 0.560) for the glaucoma patients and normal subjects were similar. The VF mean deviation was −7.61  ±  8.83 decibels (dB) for the glaucoma subjects, with a significant difference between the healthy subjects and glaucoma patients (−0.87  ±  1.39 for controls, P < 0.001) and no significant differences among subgroups divided by disc size (−6.89  ±  9.02 for small discs vs. −8.18  ±  12.02 for medium discs vs. −6.84  ±  10.61 for large discs, P = 0.777). We sorted the glaucomatous eyes according to the presence of PPA, but found no demographic differences between the two groups (Table 2). 
Table 1. 
 
Demographics of the Control Group, Glaucoma Group, and Three Subgroups according to Disc Size and Their ONH Parameters as Measured by Stratus OCT and Cirrus HD-OCT
Table 1. 
 
Demographics of the Control Group, Glaucoma Group, and Three Subgroups according to Disc Size and Their ONH Parameters as Measured by Stratus OCT and Cirrus HD-OCT
Controls (n = 28) Glaucoma (n = 78) P Value* Small Discs (n = 25) Medium Discs (n = 26) Large Discs (n = 27) P Value†
Age (y) 53.48 ± 10.74 55.72 ± 11.23 0.421 55.83 ± 12.37 52.46 ± 10.98 59.11 ± 11.56 0.612
Female/Male (n) 17:11 40:38:00 0.712 12:13 16:10 12:15 0.733
CCT (μm) 541.57 ± 28.94 542.73 ± 31.12 0.552 555.12 ± 28.81 538.40 ± 25.86 541.92 ± 30.81 0.586
Spherical equivalent (D) −0.71 ± 2.23 −0.84 ± 2.07 0.671 −0.76 ± 2.14 −0.89 ± 1.98 −1.04 ± 2.06 0.591
Axial length (mm) 23.54 ± 2.54 24.72 ± 3.01 0.56 23.31 ± 2.14 24.81 ± 2.98 25.29 ± 2.77 0.681
VF MD (dB) −0.87 ± 1.39 −7.61 ± 8.83 <0.001 −6.89 ± 9.02 −8.18 ± 12.02 −6.84 ± 10.61 0.777
VF PSD (dB) 1.41 ± 0.32 6.93 ± 4.10 <0.001 4.71 ± 3.87 5.01 ± 4.62 5.07 ± 3.81 0.862
From Cirrus OCT
 Average RNFL thickness (μm) 98.71 ± 16.43 64.56 ± 12.98 0.002 70.63 ± 15.91 74.21 ± 19.95 71.21 ± 12.21 0.81
 Disc area (mm2) 2.12 ± 0.26 2.07 ± 0.33 0.584 1.82 ± 0.13 2.12 ± 0.06 2.46 ± 0.19 <0.001
 Rim area (mm2) 1.00 ± 0.17 0.63 ± 0.27 <0.001 0.70 ± 0.29 0.75 ± 0.34 0.81 ± 0.27 0.599
 Average CDR 0.60 ± 0.27 0.81 ± 0.08 <0.001 0.76 ± 0.10 0.78 ± 0.10 0.79 ± 0.08 0.59
 Vertical CDR 0.51 ± 0.18 0.80 ± 0.09 0.006 0.72 ± 0.19 0.75 ± 0.13 0.78 ± 0.09 0.505
 Cup volume (mm3) 0.33 ± 0.18 0.59 ± 0.24 <0.001 0.45 ± 0.24 0.44±.022 0.68 ± 0.22 0.008
From Stratus OCT
 Average RNFL thickness (μm) 92.89 ± 18.36 62.43 ± 18.66 <0.001 77.96 ± 25.34 68.46 ± 22.11 64.53 ± 19.12 0.224
 Disc area (mm2) 2.48 ± 0.46 2.56 ± 0.47 0.595 1.90 ± 0.43 2.58 ± 0.41 2.97 ± 0.40 <0.001
 Cup area (mm2) 1.41 ± 0.70 2.02 ± 0.66 0.007 1.33 ± 0.35 1.95 ± 0.48 2.32 ± 0.45 0.949
 Rim area (mm2) 1.07 ± 0.46 0.53 ± 0.34 <0.001 0.53 ± 0.26 0.64 ± 0.36 0.67 ± 0.31 0.49
 Rim volume (mm3) 0.21 ± 0.15 0.06 ± 0.07 0.033 0.08 ± 0.04 0.06 ± 0.09 0.05 ± 0.04 0.165
 Cup volume (mm3) 0.15 ± 0.22 0.31 ± 0.19 0.161 0.25 ± 0.27 0.28 ± 0.14 0.36 ± 0.17 0.5
 Average CDR 0.56 ± 0.20 0.79 ± 0.14 0.001 0.63 ± 0.27 0.78 ± 0.26 0.83 ± 0.18 0.607
 Horizontal CDR 0.76 ± 0.14 0.89 ± 0.11 0.005 0.78 ± 0.19 0.84 ± 0.19 0.97 ± 0.16 0.254
 Vertical CDR 0.68 ± 0.15 0.85 ± 0.13 0.001 0.82 ± 0.15 0.87 ± 0.14 0.90 ± 0.10 0.212
Table 2. 
 
AUCs for the ONH Parameters Measured by Stratus OCT and Cirrus HD-OCT in Patients with Glaucoma and in Three Subgroups according to Disc Size
Table 2. 
 
AUCs for the ONH Parameters Measured by Stratus OCT and Cirrus HD-OCT in Patients with Glaucoma and in Three Subgroups according to Disc Size
All Discs Mean AUC ± SD (95% CI) Small Discs Mean AUC ± SD (95% CI) Medium Discs Mean AUC ± SD (95% CI) Large Discs Mean AUC ± SD (95% CI)
Disc parameters from Cirrus OCT
 RNFL thickness 0.944 ± 0.060 (0.922–0.976) 0.956 ± 0.058 (0.892–0.978) 0.931 ± 0.054 (0.906–0.955) 0.921 ± 0.047 (0.871–0.943)
 Rim area 0.936 ± 0.037 (0.914–0.972) 0.951 ± 0.038 (0.927–0.977) 0.913 ± 0.040 (0.907–0.950) 0.891 ± 0.032 (0.841–0.929)
 Average CDR 0.787 ± 0.042 (0.715–0.809) 0.748 ± 0.041 (0.729–0.829) 0.784 ± 0.038 (0.765–0.809) 0.901 ± 0.038 (0.764–0.912)
 Vertical CDR 0.740 ± 0.040 (0.721–0.828) 0.721 ± 0.037 (0.704–0.819) 0.779 ± 0.036 (0.771–0.827) 0.886 ± 0.036 (0.757–0.908)
 Cup volume 0.656 ± 0.035 (0.563–0.741) 0.533 ± 0.036 (0.501–0.635) 0.658 ± 0.038 (0.563–0.749) 0.736 ± 0.039 (0.663–0.819)
Disc parameters from Stratus OCT
 RNFL thickness 0.887 ± 0.063 (0.780–0.926) 0.903 ± 0.054 (0.818–0.942) 0.891 ± 0.057 (0.788–0.915) 0.876 ± 0.049 (0.742–0.899)
 Cup area 0.683 ± 0.032 (0.525–0.742) 0.646 ± 0.033 (0.603–0.734) 0.663 ± 0.033 (0.625–0.784) 0.709 ± 0.043 (0.637–0.812)
 Rim area 0.776 ± 0.041 (0.666–0.846) 0.800 ± 0.037 (0.714–0.855) 0.753 ± 0.041 (0.667–0.816) 0.733 ± 0.035 (0.642–0.835)
 Rim volume 0.824 ± 0.033 (0.762–0.886) 0.892 ± 0.037 (0.801–0.914) 0.811 ± 0.038 (0.762–0.838) 0.782 ± 0.038 (0.762–0.806)
 Cup volume 0.732 ± 0.031 (0.653–0.814) 0.727 ± 0.039 (0.650–0.811) 0.760 ± 0.037 (0.673–0.845) 0.812 ± 0.039 (0.753–0.891)
 Average CDR 0.701 ± 0.035 (0.628–0.810) 0.667 ± 0.042 (0.565–0.724) 0.695 ± 0.041 (0.586–0.815) 0.809 ± 0.041 (0.736–0.865)
 Horizontal CDR 0.754 ± 0.042 (0.642–0.898) 0.700 ± 0.042 (0.655–0.799) 0.795 ± 0.042 (0.709–0.890) 0.818 ± 0.042 (0.724–0.898)
 Vertical CDR 0.729 ± 0.035 (0.639–0.816) 0.705 ± 0.040 (0.642–0.816) 0.773 ± 0.035 (0.742–0.831) 0.800 ± 0.037 (0.749–0.859)
OCT Measurements
Cirrus HD-OCT (software version 5.0.0.326) uses SD technology of an optic disc cube obtained from a 3-dimensional data set, composed of 200 A-scans from each of 200 B-scans that cover a 6-mm2 area centered on the optic disc. After creating an RNFL thickness map from the cube data set, the software automatically determines the center of the disc and then extracts a circumpapillary circle (radius 1.73 mm) from the cube data set for RNFL thickness measurement. For ONH parameters, the end of Bruch's membrane was defined as the disc margin and was identified from the 3-dimensional cube data set. The rim area, disc area, average CDR, vertical CDR, and cup volume were calculated automatically and provided in a standard printout. All subjects were examined using the Optic Disc Cube 200 × 200 program with maximum pupil dilation. We excluded all poor-quality scans, defined as those with a signal strength <6, the presence of overt misalignment of the surface detection algorithm on ≥15% of consecutive A-scans or 20% of cumulative A-scans, or overt decentration of the measurement circle location, assessed subjectively. In addition, we excluded images if horizontal eye motion was observed within the measurement circle or if there was misidentification of Bruch's membrane termination. 
Stratus TD-OCT (software version 4.0.2) uses TD technology and allows the computation of topographic data derived from each individual linear optic disc scan into an integrated analysis characterizing the overall optic disc topography. The fast ONH scan protocol was used. Six radial, equally spaced scans 4 mm in length were centered at the optic disc. The disc margin was determined automatically as the end of the RPE. If artifacts were identified, such as wrong identification of the retinal or RPE plane, often involving vitreous tissue in the calculation, they were excluded. Only clear images with good-quality scores (≥ 6) were considered in this study. 
Presence of Peripapillary Atrophy
PPA was defined based on disc photographs that were acquired after maximal pupil dilation. The optic disc images were evaluated independently by two authors (HYP and CKP) who were masked in terms of patient clinical information. Each observer classified photographs into one of the two groups: eyes with and without PPA. Any discrepancy between the observers was resolved by consensus. 
Statistical Analysis
An independent t-test or one-way ANOVA was used for continuous variables, and the χ2 test was used for categoric variables to assess the differences among groups. Receiver operating characteristic (ROC) curves assessed the ability of the RNFL area index and circumpapillary RNFL thicknesses to detect glaucomatous changes. ROC analysis included calculation of the area under the curve (AUC). Differences in the diagnostic ability (AUC) were tested for statistical significance using MedCalc (MedCalc Software Inc., Mariakerke, Belgium). AUC values provide a measure of the diagnostic accuracy (i.e., sensitivity and specificity) of a test, with values from 0.5–0.7 representing low accuracy, values from 0.7–0.9 representing tests that are useful for some purposes, and values greater than 0.9 representing tests with high diagnostic accuracy. To explore the glaucomatous discrimination capabilities of the ONH parameters in patients with ONHs of different sizes, we assigned the glaucomatous patients to three subgroups according to HRT: small disc (disc area ≤2.00 mm2), medium disc (2.00–3.00 mm2), and large disc (>3.00 mm2). In addition, patients were subdivided into glaucoma groups with and without PPA according to the results of red-free photography. A Pearson correlation analysis was used to examine the associations between disc area and various other ONH parameters. The Pearson correlation analysis was applied to determine the relationship between the presence of PPA with various ONH parameters. SPSS for Windows (version 12.0.0; SPSS Inc., Chicago, IL) was used. In all analyses, P < 0.05 indicated statistical significance. 
Results
The ONH parameters for normal and glaucomatous eyes as well as the subgroups divided by disc size for both OCT modalities are shown in Table 1. In Stratus OCT, the disc area (2.56  ±  0.47 mm2) and vertical CDR (0.85  ±  0.13 mm2) tended to be higher than those determined by Cirrus OCT (2.07  ±  0.33 and 0.59  ±  0.24 mm2, respectively), while the rim area tended to be lower (0.53  ±  0.34 mm2 for Stratus OCT vs. 0.63  ±  0.27 mm2 for Cirrus OCT) in the glaucoma group. We assessed the diagnostic capacity of OCT by a comparison of the AUC (Table 3, Fig. 2). Overall, Cirrus HD-OCT showed significantly higher AUCs for all groups in most of the parameters compared to Stratus OCT. For Cirrus HD-OCT, rim area (0.936 mm2) showed the highest AUC. For Stratus OCT, rim volume (0.824 mm3) showed the highest AUC. As the disc size increased, both types of OCT showed decreased AUCs in rim and disc areas, but improved AUCs in average CDR, vertical CDR, and cup volume. 
Table 3. 
 
Demographics of the Glaucoma Subgroups according to the Presence of PPA and Their ONH Parameters as Measured by Stratus OCT and Cirrus HD-OCT
Table 3. 
 
Demographics of the Glaucoma Subgroups according to the Presence of PPA and Their ONH Parameters as Measured by Stratus OCT and Cirrus HD-OCT
Glaucoma with PPA (n = 38) Glaucoma without PPA (n = 40) P Value*
Age (y) 54.21 ± 13.44 56.73 ± 10.89 0.516
Female/male (n) 15:13 21:19 0.634
CCT (μm) 543.15 ± 25.44 541.89 ± 30.15 0.612
Spherical equivalent (D) −0.76 ± 1.80 −1.11 ± 2.41 0.384
Axial length (mm) 23.24 ± 2.87 25.01 ± 2.93 0.338
VF MD (dB) −9.65 ± 8.47 −6.75 ± 7.72 0.178
VF PSD (dB) 5.81 ± 5.19 4.07 ± 3.26 0.214
From Cirrus OCT
 Average RNFL thickness (μm) 69.43 ± 15.05 73.21 ± 16.33 0.484
 Disc area (mm2) 2.09 ± 0.29 2.10 ± 0.32 0.945
 Rim area (mm2) 0.81 ± 0.28 0.65 ± 0.33 0.087
 Average CDR 0.76 ± 0.09 0.80 ± 0.08 0.253
 Vertical CDR 0.75 ± 0.11 0.74 ± 0.19 0.853
 Cup volume (mm3) 0.48 ± 0.23 0.55 ± 0.27 0.398
From Stratus OCT
 Average RNFL thickness (μm) 65.63 ± 22.88 77.10 ± 22.13 0.144
 Disc area (mm2) 2.78 ± 0.59 2.42 ± 0.47 0.049
 Cup area (mm2) 2.33 ± 0.84 1.64 ± 0.75 0.005
 Rim area (mm2) 0.45 ± 0.36 0.81 ± 0.41 0.002
 Rim volume (mm3) 0.04 ± 0.06 0.10 ± 0.08 0.028
 Cup volume (mm3) 0.29 ± 0.24 0.31 ± 0.23 0.151
 Average CDR 0.77 ± 0.14 0.68 ± 0.18 0.017
 Horizontal CDR 0.83 ± 0.13 0.73 ± 0.14 0.009
 Vertical CDR 0.77 ± 0.15 0.70 ± 0.17 0.008
Figure 2. 
 
Box plot of AUCs for the ONH parameters measured by Stratus OCT and Cirrus HD-OCT in patients with glaucoma, and in three subgroups according to disc size. Overall, Cirrus HD-OCT showed significantly higher AUCs for all groups in most of the parameters compared to Stratus OCT. As the disc size increased, Cirrus OCT showed decreased AUCs in RNFL thickness and rim area, but improved AUCs in average CDR, and Stratus OCT showed decreased AUCs in RNFL thickness and rim volume, but improved AUCs in horizontal CDR.
Figure 2. 
 
Box plot of AUCs for the ONH parameters measured by Stratus OCT and Cirrus HD-OCT in patients with glaucoma, and in three subgroups according to disc size. Overall, Cirrus HD-OCT showed significantly higher AUCs for all groups in most of the parameters compared to Stratus OCT. As the disc size increased, Cirrus OCT showed decreased AUCs in RNFL thickness and rim area, but improved AUCs in average CDR, and Stratus OCT showed decreased AUCs in RNFL thickness and rim volume, but improved AUCs in horizontal CDR.
When glaucoma patients with and without PPA were compared, the Stratus OCT measurements showed significant differences in disc area, with larger values for the PPA group (2.78  ±  0.59 vs. 2.42  ±  0.47 mm2, P = 0.017), while there were no significant differences in the Cirrus HD-OCT measurements (2.09  ±  0.29 vs. 2.10  ±  0.32 mm2, P = 0.945, Table 2, Fig. 3). With the exception of average RNFL thickness and cup volume, other parameters also were significantly different between the groups by Stratus OCT (cup area P = 0.049, rim area P = 0.002, rim volume P = 0.028, and average CDR P = 0.017). Disc area showed significant differences between Stratus OCT and Cirrus HD-OCT in the glaucoma and PPA groups (P < 0.01 in both groups). Rim area and cup volume were significantly different between Stratus OCT and Cirrus HD-OCT (P = 0.07 and P < 0.01, respectively). AUC comparisons between the two groups were different for both types of OCT (Table 4, Fig. 4). Notably, the AUCs for Stratus OCT were significantly poorer in the glaucoma with PPA groups (RNFL thickness P < 0.001, cup area P < 0.001, rim area P < 0.001, rim volume P < 0.001, cup volume P < 0.031, average CDR P < 0.001, horizontal CDR P < 0.001, and vertical CDR P < 0.001). On the other hand, the AUCs for Cirrus OCT showed no significant differences between the two groups except the AUC of RNFL thickness (RNFL thickness P < 0.001, rim area P = 0.356, average CDR P = 0.642, vertical CDR P = 0.723, and cup volume P = 0.751). In the glaucoma with PPA group, the AUCs of RNFL thickness in cirrus OCT showed a statistically significant decrease compared to glaucoma without PPA group (0.816 vs. 0.944, P < 0.001), though both of these are greater than AUCs of Stratus OCT. In Cirrus OCT, RNFL thickness proved to have better diagnostic ability than rim area in the glaucoma without PPA group (0.944 for RNFL thickness vs. 0.930 for rim area), while rim area had better results in the glaucoma with PPA group (0.816 for RNFL thickness vs. 0.871 for rim area). 
Figure 3. 
 
Box plots of the ONH parameters as measured by Stratus OCT and Cirrus HD-OCT in the glaucoma subgroups according to the presence of PPA. Disc area, rim area, and cup volume were significantly different between Stratus OCT and Cirrus HD-OCT in the glaucoma with PPA group. These also were significantly different between the groups by Stratus OCT. *P value < 0.05.
Figure 3. 
 
Box plots of the ONH parameters as measured by Stratus OCT and Cirrus HD-OCT in the glaucoma subgroups according to the presence of PPA. Disc area, rim area, and cup volume were significantly different between Stratus OCT and Cirrus HD-OCT in the glaucoma with PPA group. These also were significantly different between the groups by Stratus OCT. *P value < 0.05.
Table 4. 
 
AUCs of the ONH Parameters Measured by Stratus OCT and Cirrus HD-OCT in the Glaucoma Subgroups according to the Presence of PPA
Table 4. 
 
AUCs of the ONH Parameters Measured by Stratus OCT and Cirrus HD-OCT in the Glaucoma Subgroups according to the Presence of PPA
Glaucoma with PPA Glaucoma without PPA P Value*
Mean AUC ± SD (95% CI) Mean AUC ± SD (95% CI)
Disc parameters from Cirrus OCT
 RNFL thickness 0.816 ± 0.047 (0.716–0.898) 0.944 ± 0.065 (0.817–0.973) <0.001
 Rim area 0.871 ± 0.032 (0.730–0.912) 0.930 ± 0.035 (0.845–0.961) 0.356
 Average CDR 0.724 ± 0.039 (0.613–0.817) 0.775 ± 0.041 (0.626–0.883) 0.642
 Vertical CDR 0.762 ± 0.045 (0.596–0.819) 0.789 ± 0.038 (0.619–0.960) 0.723
 Cup volume 0.673 ± 0.034 (0.509–0.773) 0.637 ± 0.042 (0.538–0.736) 0.751
Disc parameters from Stratus OCT
 RNFL thickness 0.603 ± 0.051 (0.478–0.716) 0.706 ± 0.047 (0.586–0.831) <0.001
 Cup area 0.434 ± 0.039 (0.356–0.568) 0.641 ± 0.040 (0.540–0.742) <0.001
 Rim area 0.566 ± 0.042 (0.446–0.686) 0.712 ± 0.038 (0.639–0.870) <0.001
 Rim volume 0.481 ± 0.033 (0.339–0.529) 0.707 ± 0.038 (0.615–0.838) <0.001
 Cup volume 0.523 ± 0.032 (0.485–0.661) 0.690 ± 0.031 (0.588–0.793) 0.031
 Average CDR 0.401 ± 0.041 (0.387–0.516) 0.740 ± 0.041 (0.662–0.818) <0.001
 Horizontal CDR 0.385 ± 0.039 (0.272–0.498) 0.725 ± 0.039 (0.649–0.802) <0.001
 Vertical CDR 0.447 ± 0.037 (0.319–0.576) 0.753 ± 0.030 (0.677–0.830) <0.001
Figure 4. 
 
Box plots of AUCs for the ONH parameters measured by Stratus OCT and Cirrus HD-OCT in the glaucoma subgroups according to the presence of PPA. The AUCs of RNFL thickness, rim-related parameter (rim area and rim volume) and average CDR for both OCTs were poorer in the glaucoma with PPA group. AUC comparisons between the two groups showed significant differences for Stratus OCT. In Cirrus OCT, the AUC of RNFL thickness in the PPA group showed a statistically significant decrease compared to the glaucoma without PPA group. In Cirrus OCT, RNFL thickness proved to have better diagnostic ability than rim area in the glaucoma without PPA group while rim area had better results in the glaucoma with PPA group. The AUCs of these ONH parameters for Cirrus OCT showed greater diagnostic ability than for Stratus OCT. *P value < 0.05.
Figure 4. 
 
Box plots of AUCs for the ONH parameters measured by Stratus OCT and Cirrus HD-OCT in the glaucoma subgroups according to the presence of PPA. The AUCs of RNFL thickness, rim-related parameter (rim area and rim volume) and average CDR for both OCTs were poorer in the glaucoma with PPA group. AUC comparisons between the two groups showed significant differences for Stratus OCT. In Cirrus OCT, the AUC of RNFL thickness in the PPA group showed a statistically significant decrease compared to the glaucoma without PPA group. In Cirrus OCT, RNFL thickness proved to have better diagnostic ability than rim area in the glaucoma without PPA group while rim area had better results in the glaucoma with PPA group. The AUCs of these ONH parameters for Cirrus OCT showed greater diagnostic ability than for Stratus OCT. *P value < 0.05.
Pearson correlation analysis indicated that disc area was associated independently with several ONH parameters in Stratus OCT, especially in the PPA group (correlation coefficients for cup area 0.918, P < 0.001; rim area −0.418, P = 0.015; rim volume −0.646, P < 0.001; cup volume 0.743, P < 0.001; average CDR 0.409, P < 0.001; horizontal CDR 0.654, P < 0.001; and vertical CDR 0.562, P = 0.019, Table 5). These observations indicated that the accuracy of the figures was dependent on disc size. 
Table 5. 
 
Pearson Correlation Analysis of the Disc Area (Dependent Variable) with Other ONH Parameters (Independent Variables) for Both Types of OCT
Table 5. 
 
Pearson Correlation Analysis of the Disc Area (Dependent Variable) with Other ONH Parameters (Independent Variables) for Both Types of OCT
All Glaucoma Glaucoma with PPA
R P Value R P Value
Cirrus OCT Rim area 0.123 0.409 0.143 0.37
Average CDR 0.299 0.18 0.344 0.217
Vertical CDR 0.178 0.23 0.256 0.32
Cup volume 0.384 0.108 0.349 0.142
Stratus OCT Cup area 0.096 0.522 0.918 <0.001
Rim area −0.327 0.025 −0.418 0.015
Rim volume −0.638 <0.001 −0.646 <0.001
Cup volume 0.324 0.026 0.743 <0.001
Average CDR 0.305 0.037 0.409 <0.001
Horizontal CDR 0.786 <0.001 0.654 <0.001
Vertical CDR 0.592 <0.001 0.562 0.019
Discussion
At present, there is no gold standard for diagnosing glaucoma. Often, visualization of a change on optic disc photography, which may take years to occur, and VF defects seen on achromatic automated perimetry, which may not show up until many retinal nerve fibers already have been lost, are used to define glaucoma. 20 OCT has great potential for diagnosing glaucoma and glaucomatous progression. 5,21,22 The level of discrimination (in micrometers) potentially makes OCT an objective tool for diagnosing axonal loss. Optic disc size may differ by >7-fold among normal individuals, ranging from 0.8–6.0 mm2. 23 Previous histologic studies showed that the optic nerve fiber count increases with increasing ONH size. 2426 In some cases, even experts may have trouble determining the cup border, due to the various morphology as well as the size of the disc. The calculation is not possible at all if the disc is tilted. Progression involving only deepening of the cup cannot be detected, as it is not possible to determine the depth of the cup from cross-sectional images. Therefore, these aspects have been overlooked despite the importance of ONH assessment. Thus, new imaging modalities that can provide a quantitative and reproducible objective assessment of the ONH are required. 
The lack of enthusiasm for using ONH parameters measured by Stratus OCT probably stems from the low reproducibility of ONH scans and weaknesses of the Stratus OCT ONH analysis algorithm (e.g., misidentification of the optic disc margin and vitreoretinal boundary, and occasional inclusion of non-optic disk tissue, such as vitreous tuft as rim tissue), which require manual correction. Many reports have compared both OCTs to fundus planimetry. Samarawickrama et al. reported that linear and area measures by Stratus OCT were approximately 10% smaller than digital planimetry measurements; however, all 3 CDRs were preserved. 27 A small number of 0 and very small vertical cup diameter measures that OCT recorded could have been one of the factors responsible for discrepancy between the OCT method and planimetry of disc photographs. It was suggested that digital planimetry might be more sensitive than OCT in detecting small, physiologically normal optic cups and hence small CDRs. On the other hand, Kotera et al. reported that disc margins on fundus photographs corresponded to termination of the highly reflective straight line on the SD-OCT images at 99.3% of the positions along the disc edges. 28 Cup margins on fundus photographs corresponded at 73.6% of the positions to the interior border of the hyporeflexive regions on the OCT fundus images in their study. Good discrimination was reported using the Stratus OCT for rim volume and vertical integrated rim area (VIRA) by Sihota et al., with AUCs of 0.889 and 0.835, respectively. 29 The lowest ability of ONH parameters to distinguish normal from mildly affected eyes using Stratus OCT was reported by Chen and Huang, 30 and Huang and Chen. 31 The largest AUCs for the best discriminants in these two studies were 0.728 and 0.737 for vertical CDR, 0.711 and 0.724 for CDR, and 0.691 and 0.707 for rim area, respectively, with sensitivities not exceeding 60.5% in either study. Altogether, previous reports using Stratus OCT showed that VIRA, rim area, and vertical CDR seem to be the most frequent among the three best ONH parameters, but studies have yet to find a single consistent ONH parameter to be used for glaucoma detection and progression. 19  
In this study, most of the ONH parameters were superior in Cirrus HD-OCT when compared to Stratus OCT. There was an even greater advantage in eyes with PPA, likely due to a more accurate measurement of disc area. Advanced axial resolution in each new OCT system over that of the previous generation could be the reason for this improvement in systems of different OCT generations. The axial resolution of Cirrus HD-OCT (5 μm) also is higher than that of Stratus OCT (7–10 μm). Increased resolution leads to better visualization of the opening of Bruch's membrane. 32 Cirrus OCT defines the optic disc margin as the end of Bruch's membrane, not by RPE termination. In contrast, in Stratus OCT, the optic disc margin is determined by connecting the ends of the RPE layer; therefore, PPA devoid of RPE, a common feature of a glaucomatous optic disc, sometimes is prone to misidentification as the disc area (Fig. 1). Moreover, in Stratus OCT, major blood vessels around the optic disc may hinder the acquisition of good quality images, and radial B-scan images, only 6 in quantity, may lead to inaccurate determination of the optic disc and cup size. 32 In a previous report, an erroneous automatic recognition of the disc margin was observed in 53% of the tested eyes, which resulted in pronounced disc shape and size misalignment. 29 In Cirrus OCT, the rim width around the circumference of the optic disc is then determined by measuring the amount of neuroretinal tissue in the optic nerve. 33 This differs from Stratus OCT, which determines the cup margin based on its intersection with a plane at a fixed distance above the disc. The cup margin is determined arbitrarily by the reference plane, which is defined as lying 150 μm anterior to the line connecting the ends of the RPE. An arbitrarily defined cup reference plane may not represent the actual cup margin. As a consequence, erroneous automatic recognition of the disc margin results in the inaccurate measurement of all other ONH parameters. Hence, the development of specific software for ONH analysis by Cirrus HD-OCT is a remarkable update for this instrument. 
In a Cirrus OCT study by Mwanza et al., which included 73 subjects with glaucoma and 146 age-matched normal controls, there were no differences in the ability of ONH parameters and RNFL thickness measurements, as measured by Cirrus OCT, to distinguish between normal and glaucomatous eyes. 19 They found the AUC for distinguishing between normal eyes and eyes with mild glaucoma was greatest for the 7-clock-hour RNFL thickness (0.918), VRT (0.914), rim area (0.912), RNFL thickness of the inferior quadrant (0.895), average RNFL thickness (0.893), and vertical CDR (0.890). Recent studies of RNFL thickness measurements have shown that the diagnostic sensitivity and specificity of Cirrus HD-OCT are similar to those of TD-OCT. 3437 Only one study found better values for SD-OCT than TD-OCT. 38 As a result, Cirrus OCT offers improved results for ONH parameters other than RNFL thickness compared to Stratus OCT, as the ONH parameters showed better results by Cirrus OCT in our study. Because previous studies with Stratus OCT have indicated increased sensitivity in detecting glaucoma after combining data from RNFL thickness and ONH measurements, it can be inferred that combining the same data will enhance the diagnostic performance of Cirrus HD-OCT. 10,39  
It is significant for glaucoma diagnosis that Cirrus HD-OCT showed improved performance compared to Stratus OCT in our study, especially in glaucomatous patients. This is because the β-zone of peripapillary chorioretinal atrophy, which is atrophy of the RPE and choriocapillaris, is a more common feature in glaucomatous eyes and is correlated spatially with neuroretinal rim loss in the intrapapillary region. In previous studies, the frequencies of β-zone PPA in chronic primary open-angle glaucoma patients and normal tension glaucoma (NTG) patients (62.4 and 84%, respectively) indicated high prevalence rates compared to the frequency of 15% in normal patients. 40 PPA, which has high sensitivity for glaucoma detection, may be used as a method of early glaucoma detection. PPA also is a prognostic factor for NTG progression, and the area and extent of the β-zone increase significantly with increasing visual field defects. 41,42 Therefore, the improved distinction between disc area and PPA by Cirrus OCT has greater significance in glaucomatous eyes than in normal eyes. 
In our study, diagnostic ability of RNFL thickness in Cirrus OCT, using the more widely accepted diagnostic measure, was significantly greater than in Stratus OCT. There were significant differences according to PPA in the diagnostic ability of RNFL thickness for both OCTs. In Cirrus OCT, RNFL thickness showed poorer diagnostic ability than rim area in the glaucoma with PPA group. 
We performed a comparison of ONH parameters according to disc size. A smaller disc area was related to a smaller rim area, smaller CDR, thinner RNFL, smaller cup volume, and smaller average CDR. A recent study indicated that optic disc size was an important parameter with the strongest influence on ONH and RNFL measurements. 43 Therefore, we speculated that the cup was too small to distinguish related measurements in the small disc. The strong effect of disc area on ONH and RNFL measurements suggests that optic disc size also should be considered in the assessment of glaucoma. Further study is necessary to investigate differences in the assessment of glaucoma according to disc size. The diagnostic accuracy estimates in our study cannot be applied completely to clinical practice because our study included only patients with confirmed visual field loss compared to normal subjects. Diagnostic tests are to be used in patients with suspected disease rather than in patients with a confirmed diagnosis; therefore, the diagnostic accuracies of both types of OCT in detecting glaucoma may have been overestimated. Medeiros et al. suggested that the population studied and reference standard used to define disease may have a large effect on the accuracy of diagnostic tests for glaucoma. 44 Therefore, in preperimetric glaucoma, there can be much limitation in applying AUC of both modalities. Localized notching of rim and correspondent RNFL thinning can be the only factor of assessment, and these small changes might not be reflected by the rim area of ONH parameter. 45 Diagnostic abilities in both modalities are expected to be low because there is difficulty in diagnosing preperimetric glaucoma by optic nerve parameter, especially in case of a non-glaucomatous disc and showing only localized RNFL defect. Nevertheless, the difference occurring from the both modalities according to PPA is assumed to be applied, not only to preperimetric glaucoma, but also to ONH of the normal eyes. Our results support the suggestion that Cirrus OCT has advantages over Stratus OCT in glaucoma detection. 
Cirrus HD-OCT showed better overall glaucoma diagnostic ability than Stratus OCT. Ophthalmologists should pay special attention to interpreting the ONH parameters obtained by Stratus OCT, which tend to overestimate the size of the optic disc in glaucomatous patients with PPA. 
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Footnotes
 Disclosure: S.Y. Kim, None; H.-Y.L. Park, None; C.K. Park, None
Figure 1. 
 
Images of identical ONHs by Heidelberg SL-OCT (top), TD-OCT (middle), and SD-OCT (bottom). The Heidelberg SL-OCT used as a landmark for ONH morphometry enables detailed imaging of the ONH, displaying not only the RPE but also Bruch's membrane. Yellow arrows: The border of Bruch's membrane, which is the actual disc margin. Red arrows: The border of the RPE, which is defined as the PPA margin. As Stratus OCT (middle image) determined the disc margin by the RPE, it misidentified areas devoid of RPE as disc area and marked the disc including the PPA area (light blue straight line). The cup was calculated arbitrarily as the area where the parallel line 150 μm above the light blue line (red straight line) and the inner margin (light blue curved line) meet. In contrast, Cirrus OCT, which produced fewer artifacts, was better able to visualize Bruch's membrane and, therefore, described the disc margin precisely (black dots). As the cup margin was determined according to the direct measurement of retinal nerve fibers, it was not parallel to the disc margin and was more accurate.
Figure 1. 
 
Images of identical ONHs by Heidelberg SL-OCT (top), TD-OCT (middle), and SD-OCT (bottom). The Heidelberg SL-OCT used as a landmark for ONH morphometry enables detailed imaging of the ONH, displaying not only the RPE but also Bruch's membrane. Yellow arrows: The border of Bruch's membrane, which is the actual disc margin. Red arrows: The border of the RPE, which is defined as the PPA margin. As Stratus OCT (middle image) determined the disc margin by the RPE, it misidentified areas devoid of RPE as disc area and marked the disc including the PPA area (light blue straight line). The cup was calculated arbitrarily as the area where the parallel line 150 μm above the light blue line (red straight line) and the inner margin (light blue curved line) meet. In contrast, Cirrus OCT, which produced fewer artifacts, was better able to visualize Bruch's membrane and, therefore, described the disc margin precisely (black dots). As the cup margin was determined according to the direct measurement of retinal nerve fibers, it was not parallel to the disc margin and was more accurate.
Figure 2. 
 
Box plot of AUCs for the ONH parameters measured by Stratus OCT and Cirrus HD-OCT in patients with glaucoma, and in three subgroups according to disc size. Overall, Cirrus HD-OCT showed significantly higher AUCs for all groups in most of the parameters compared to Stratus OCT. As the disc size increased, Cirrus OCT showed decreased AUCs in RNFL thickness and rim area, but improved AUCs in average CDR, and Stratus OCT showed decreased AUCs in RNFL thickness and rim volume, but improved AUCs in horizontal CDR.
Figure 2. 
 
Box plot of AUCs for the ONH parameters measured by Stratus OCT and Cirrus HD-OCT in patients with glaucoma, and in three subgroups according to disc size. Overall, Cirrus HD-OCT showed significantly higher AUCs for all groups in most of the parameters compared to Stratus OCT. As the disc size increased, Cirrus OCT showed decreased AUCs in RNFL thickness and rim area, but improved AUCs in average CDR, and Stratus OCT showed decreased AUCs in RNFL thickness and rim volume, but improved AUCs in horizontal CDR.
Figure 3. 
 
Box plots of the ONH parameters as measured by Stratus OCT and Cirrus HD-OCT in the glaucoma subgroups according to the presence of PPA. Disc area, rim area, and cup volume were significantly different between Stratus OCT and Cirrus HD-OCT in the glaucoma with PPA group. These also were significantly different between the groups by Stratus OCT. *P value < 0.05.
Figure 3. 
 
Box plots of the ONH parameters as measured by Stratus OCT and Cirrus HD-OCT in the glaucoma subgroups according to the presence of PPA. Disc area, rim area, and cup volume were significantly different between Stratus OCT and Cirrus HD-OCT in the glaucoma with PPA group. These also were significantly different between the groups by Stratus OCT. *P value < 0.05.
Figure 4. 
 
Box plots of AUCs for the ONH parameters measured by Stratus OCT and Cirrus HD-OCT in the glaucoma subgroups according to the presence of PPA. The AUCs of RNFL thickness, rim-related parameter (rim area and rim volume) and average CDR for both OCTs were poorer in the glaucoma with PPA group. AUC comparisons between the two groups showed significant differences for Stratus OCT. In Cirrus OCT, the AUC of RNFL thickness in the PPA group showed a statistically significant decrease compared to the glaucoma without PPA group. In Cirrus OCT, RNFL thickness proved to have better diagnostic ability than rim area in the glaucoma without PPA group while rim area had better results in the glaucoma with PPA group. The AUCs of these ONH parameters for Cirrus OCT showed greater diagnostic ability than for Stratus OCT. *P value < 0.05.
Figure 4. 
 
Box plots of AUCs for the ONH parameters measured by Stratus OCT and Cirrus HD-OCT in the glaucoma subgroups according to the presence of PPA. The AUCs of RNFL thickness, rim-related parameter (rim area and rim volume) and average CDR for both OCTs were poorer in the glaucoma with PPA group. AUC comparisons between the two groups showed significant differences for Stratus OCT. In Cirrus OCT, the AUC of RNFL thickness in the PPA group showed a statistically significant decrease compared to the glaucoma without PPA group. In Cirrus OCT, RNFL thickness proved to have better diagnostic ability than rim area in the glaucoma without PPA group while rim area had better results in the glaucoma with PPA group. The AUCs of these ONH parameters for Cirrus OCT showed greater diagnostic ability than for Stratus OCT. *P value < 0.05.
Table 1. 
 
Demographics of the Control Group, Glaucoma Group, and Three Subgroups according to Disc Size and Their ONH Parameters as Measured by Stratus OCT and Cirrus HD-OCT
Table 1. 
 
Demographics of the Control Group, Glaucoma Group, and Three Subgroups according to Disc Size and Their ONH Parameters as Measured by Stratus OCT and Cirrus HD-OCT
Controls (n = 28) Glaucoma (n = 78) P Value* Small Discs (n = 25) Medium Discs (n = 26) Large Discs (n = 27) P Value†
Age (y) 53.48 ± 10.74 55.72 ± 11.23 0.421 55.83 ± 12.37 52.46 ± 10.98 59.11 ± 11.56 0.612
Female/Male (n) 17:11 40:38:00 0.712 12:13 16:10 12:15 0.733
CCT (μm) 541.57 ± 28.94 542.73 ± 31.12 0.552 555.12 ± 28.81 538.40 ± 25.86 541.92 ± 30.81 0.586
Spherical equivalent (D) −0.71 ± 2.23 −0.84 ± 2.07 0.671 −0.76 ± 2.14 −0.89 ± 1.98 −1.04 ± 2.06 0.591
Axial length (mm) 23.54 ± 2.54 24.72 ± 3.01 0.56 23.31 ± 2.14 24.81 ± 2.98 25.29 ± 2.77 0.681
VF MD (dB) −0.87 ± 1.39 −7.61 ± 8.83 <0.001 −6.89 ± 9.02 −8.18 ± 12.02 −6.84 ± 10.61 0.777
VF PSD (dB) 1.41 ± 0.32 6.93 ± 4.10 <0.001 4.71 ± 3.87 5.01 ± 4.62 5.07 ± 3.81 0.862
From Cirrus OCT
 Average RNFL thickness (μm) 98.71 ± 16.43 64.56 ± 12.98 0.002 70.63 ± 15.91 74.21 ± 19.95 71.21 ± 12.21 0.81
 Disc area (mm2) 2.12 ± 0.26 2.07 ± 0.33 0.584 1.82 ± 0.13 2.12 ± 0.06 2.46 ± 0.19 <0.001
 Rim area (mm2) 1.00 ± 0.17 0.63 ± 0.27 <0.001 0.70 ± 0.29 0.75 ± 0.34 0.81 ± 0.27 0.599
 Average CDR 0.60 ± 0.27 0.81 ± 0.08 <0.001 0.76 ± 0.10 0.78 ± 0.10 0.79 ± 0.08 0.59
 Vertical CDR 0.51 ± 0.18 0.80 ± 0.09 0.006 0.72 ± 0.19 0.75 ± 0.13 0.78 ± 0.09 0.505
 Cup volume (mm3) 0.33 ± 0.18 0.59 ± 0.24 <0.001 0.45 ± 0.24 0.44±.022 0.68 ± 0.22 0.008
From Stratus OCT
 Average RNFL thickness (μm) 92.89 ± 18.36 62.43 ± 18.66 <0.001 77.96 ± 25.34 68.46 ± 22.11 64.53 ± 19.12 0.224
 Disc area (mm2) 2.48 ± 0.46 2.56 ± 0.47 0.595 1.90 ± 0.43 2.58 ± 0.41 2.97 ± 0.40 <0.001
 Cup area (mm2) 1.41 ± 0.70 2.02 ± 0.66 0.007 1.33 ± 0.35 1.95 ± 0.48 2.32 ± 0.45 0.949
 Rim area (mm2) 1.07 ± 0.46 0.53 ± 0.34 <0.001 0.53 ± 0.26 0.64 ± 0.36 0.67 ± 0.31 0.49
 Rim volume (mm3) 0.21 ± 0.15 0.06 ± 0.07 0.033 0.08 ± 0.04 0.06 ± 0.09 0.05 ± 0.04 0.165
 Cup volume (mm3) 0.15 ± 0.22 0.31 ± 0.19 0.161 0.25 ± 0.27 0.28 ± 0.14 0.36 ± 0.17 0.5
 Average CDR 0.56 ± 0.20 0.79 ± 0.14 0.001 0.63 ± 0.27 0.78 ± 0.26 0.83 ± 0.18 0.607
 Horizontal CDR 0.76 ± 0.14 0.89 ± 0.11 0.005 0.78 ± 0.19 0.84 ± 0.19 0.97 ± 0.16 0.254
 Vertical CDR 0.68 ± 0.15 0.85 ± 0.13 0.001 0.82 ± 0.15 0.87 ± 0.14 0.90 ± 0.10 0.212
Table 2. 
 
AUCs for the ONH Parameters Measured by Stratus OCT and Cirrus HD-OCT in Patients with Glaucoma and in Three Subgroups according to Disc Size
Table 2. 
 
AUCs for the ONH Parameters Measured by Stratus OCT and Cirrus HD-OCT in Patients with Glaucoma and in Three Subgroups according to Disc Size
All Discs Mean AUC ± SD (95% CI) Small Discs Mean AUC ± SD (95% CI) Medium Discs Mean AUC ± SD (95% CI) Large Discs Mean AUC ± SD (95% CI)
Disc parameters from Cirrus OCT
 RNFL thickness 0.944 ± 0.060 (0.922–0.976) 0.956 ± 0.058 (0.892–0.978) 0.931 ± 0.054 (0.906–0.955) 0.921 ± 0.047 (0.871–0.943)
 Rim area 0.936 ± 0.037 (0.914–0.972) 0.951 ± 0.038 (0.927–0.977) 0.913 ± 0.040 (0.907–0.950) 0.891 ± 0.032 (0.841–0.929)
 Average CDR 0.787 ± 0.042 (0.715–0.809) 0.748 ± 0.041 (0.729–0.829) 0.784 ± 0.038 (0.765–0.809) 0.901 ± 0.038 (0.764–0.912)
 Vertical CDR 0.740 ± 0.040 (0.721–0.828) 0.721 ± 0.037 (0.704–0.819) 0.779 ± 0.036 (0.771–0.827) 0.886 ± 0.036 (0.757–0.908)
 Cup volume 0.656 ± 0.035 (0.563–0.741) 0.533 ± 0.036 (0.501–0.635) 0.658 ± 0.038 (0.563–0.749) 0.736 ± 0.039 (0.663–0.819)
Disc parameters from Stratus OCT
 RNFL thickness 0.887 ± 0.063 (0.780–0.926) 0.903 ± 0.054 (0.818–0.942) 0.891 ± 0.057 (0.788–0.915) 0.876 ± 0.049 (0.742–0.899)
 Cup area 0.683 ± 0.032 (0.525–0.742) 0.646 ± 0.033 (0.603–0.734) 0.663 ± 0.033 (0.625–0.784) 0.709 ± 0.043 (0.637–0.812)
 Rim area 0.776 ± 0.041 (0.666–0.846) 0.800 ± 0.037 (0.714–0.855) 0.753 ± 0.041 (0.667–0.816) 0.733 ± 0.035 (0.642–0.835)
 Rim volume 0.824 ± 0.033 (0.762–0.886) 0.892 ± 0.037 (0.801–0.914) 0.811 ± 0.038 (0.762–0.838) 0.782 ± 0.038 (0.762–0.806)
 Cup volume 0.732 ± 0.031 (0.653–0.814) 0.727 ± 0.039 (0.650–0.811) 0.760 ± 0.037 (0.673–0.845) 0.812 ± 0.039 (0.753–0.891)
 Average CDR 0.701 ± 0.035 (0.628–0.810) 0.667 ± 0.042 (0.565–0.724) 0.695 ± 0.041 (0.586–0.815) 0.809 ± 0.041 (0.736–0.865)
 Horizontal CDR 0.754 ± 0.042 (0.642–0.898) 0.700 ± 0.042 (0.655–0.799) 0.795 ± 0.042 (0.709–0.890) 0.818 ± 0.042 (0.724–0.898)
 Vertical CDR 0.729 ± 0.035 (0.639–0.816) 0.705 ± 0.040 (0.642–0.816) 0.773 ± 0.035 (0.742–0.831) 0.800 ± 0.037 (0.749–0.859)
Table 3. 
 
Demographics of the Glaucoma Subgroups according to the Presence of PPA and Their ONH Parameters as Measured by Stratus OCT and Cirrus HD-OCT
Table 3. 
 
Demographics of the Glaucoma Subgroups according to the Presence of PPA and Their ONH Parameters as Measured by Stratus OCT and Cirrus HD-OCT
Glaucoma with PPA (n = 38) Glaucoma without PPA (n = 40) P Value*
Age (y) 54.21 ± 13.44 56.73 ± 10.89 0.516
Female/male (n) 15:13 21:19 0.634
CCT (μm) 543.15 ± 25.44 541.89 ± 30.15 0.612
Spherical equivalent (D) −0.76 ± 1.80 −1.11 ± 2.41 0.384
Axial length (mm) 23.24 ± 2.87 25.01 ± 2.93 0.338
VF MD (dB) −9.65 ± 8.47 −6.75 ± 7.72 0.178
VF PSD (dB) 5.81 ± 5.19 4.07 ± 3.26 0.214
From Cirrus OCT
 Average RNFL thickness (μm) 69.43 ± 15.05 73.21 ± 16.33 0.484
 Disc area (mm2) 2.09 ± 0.29 2.10 ± 0.32 0.945
 Rim area (mm2) 0.81 ± 0.28 0.65 ± 0.33 0.087
 Average CDR 0.76 ± 0.09 0.80 ± 0.08 0.253
 Vertical CDR 0.75 ± 0.11 0.74 ± 0.19 0.853
 Cup volume (mm3) 0.48 ± 0.23 0.55 ± 0.27 0.398
From Stratus OCT
 Average RNFL thickness (μm) 65.63 ± 22.88 77.10 ± 22.13 0.144
 Disc area (mm2) 2.78 ± 0.59 2.42 ± 0.47 0.049
 Cup area (mm2) 2.33 ± 0.84 1.64 ± 0.75 0.005
 Rim area (mm2) 0.45 ± 0.36 0.81 ± 0.41 0.002
 Rim volume (mm3) 0.04 ± 0.06 0.10 ± 0.08 0.028
 Cup volume (mm3) 0.29 ± 0.24 0.31 ± 0.23 0.151
 Average CDR 0.77 ± 0.14 0.68 ± 0.18 0.017
 Horizontal CDR 0.83 ± 0.13 0.73 ± 0.14 0.009
 Vertical CDR 0.77 ± 0.15 0.70 ± 0.17 0.008
Table 4. 
 
AUCs of the ONH Parameters Measured by Stratus OCT and Cirrus HD-OCT in the Glaucoma Subgroups according to the Presence of PPA
Table 4. 
 
AUCs of the ONH Parameters Measured by Stratus OCT and Cirrus HD-OCT in the Glaucoma Subgroups according to the Presence of PPA
Glaucoma with PPA Glaucoma without PPA P Value*
Mean AUC ± SD (95% CI) Mean AUC ± SD (95% CI)
Disc parameters from Cirrus OCT
 RNFL thickness 0.816 ± 0.047 (0.716–0.898) 0.944 ± 0.065 (0.817–0.973) <0.001
 Rim area 0.871 ± 0.032 (0.730–0.912) 0.930 ± 0.035 (0.845–0.961) 0.356
 Average CDR 0.724 ± 0.039 (0.613–0.817) 0.775 ± 0.041 (0.626–0.883) 0.642
 Vertical CDR 0.762 ± 0.045 (0.596–0.819) 0.789 ± 0.038 (0.619–0.960) 0.723
 Cup volume 0.673 ± 0.034 (0.509–0.773) 0.637 ± 0.042 (0.538–0.736) 0.751
Disc parameters from Stratus OCT
 RNFL thickness 0.603 ± 0.051 (0.478–0.716) 0.706 ± 0.047 (0.586–0.831) <0.001
 Cup area 0.434 ± 0.039 (0.356–0.568) 0.641 ± 0.040 (0.540–0.742) <0.001
 Rim area 0.566 ± 0.042 (0.446–0.686) 0.712 ± 0.038 (0.639–0.870) <0.001
 Rim volume 0.481 ± 0.033 (0.339–0.529) 0.707 ± 0.038 (0.615–0.838) <0.001
 Cup volume 0.523 ± 0.032 (0.485–0.661) 0.690 ± 0.031 (0.588–0.793) 0.031
 Average CDR 0.401 ± 0.041 (0.387–0.516) 0.740 ± 0.041 (0.662–0.818) <0.001
 Horizontal CDR 0.385 ± 0.039 (0.272–0.498) 0.725 ± 0.039 (0.649–0.802) <0.001
 Vertical CDR 0.447 ± 0.037 (0.319–0.576) 0.753 ± 0.030 (0.677–0.830) <0.001
Table 5. 
 
Pearson Correlation Analysis of the Disc Area (Dependent Variable) with Other ONH Parameters (Independent Variables) for Both Types of OCT
Table 5. 
 
Pearson Correlation Analysis of the Disc Area (Dependent Variable) with Other ONH Parameters (Independent Variables) for Both Types of OCT
All Glaucoma Glaucoma with PPA
R P Value R P Value
Cirrus OCT Rim area 0.123 0.409 0.143 0.37
Average CDR 0.299 0.18 0.344 0.217
Vertical CDR 0.178 0.23 0.256 0.32
Cup volume 0.384 0.108 0.349 0.142
Stratus OCT Cup area 0.096 0.522 0.918 <0.001
Rim area −0.327 0.025 −0.418 0.015
Rim volume −0.638 <0.001 −0.646 <0.001
Cup volume 0.324 0.026 0.743 <0.001
Average CDR 0.305 0.037 0.409 <0.001
Horizontal CDR 0.786 <0.001 0.654 <0.001
Vertical CDR 0.592 <0.001 0.562 0.019
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