May 2010
Volume 51, Issue 5
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Retina  |   May 2010
Comparison of Retinal Thickness in Normal Eyes Using Stratus and Spectralis Optical Coherence Tomography
Author Affiliations & Notes
  • Sandeep Grover
    From the Department of Ophthalmology, College of Medicine, University of Florida, Jacksonville, Florida.
  • Ravi K. Murthy
    From the Department of Ophthalmology, College of Medicine, University of Florida, Jacksonville, Florida.
  • Vikram S. Brar
    From the Department of Ophthalmology, College of Medicine, University of Florida, Jacksonville, Florida.
  • Kakarla V. Chalam
    From the Department of Ophthalmology, College of Medicine, University of Florida, Jacksonville, Florida.
  • Corresponding author: Sandeep Grover, Department of Ophthalmology, College of Medicine, University of Florida, 580 W. 8th Street, Jacksonville, FL 32209; sgrover@jax.ufl.edu
Investigative Ophthalmology & Visual Science May 2010, Vol.51, 2644-2647. doi:10.1167/iovs.09-4774
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      Sandeep Grover, Ravi K. Murthy, Vikram S. Brar, Kakarla V. Chalam; Comparison of Retinal Thickness in Normal Eyes Using Stratus and Spectralis Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2010;51(5):2644-2647. doi: 10.1167/iovs.09-4774.

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

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Abstract

Purpose.: Spectral-domain optical coherence tomography (SD-OCT) is an advancement over time-domain OCT (TD-OCT) in the imaging of retinal disorders. Retinal thickness measured by SD-OCT differs from that measured by TD-OCT because the delineation of the outer boundary of the retina differs in the two instruments. The present study aims to evaluate this difference by comparing macular thickness, as obtained by Stratus and Spectralis OCT, in subjects without any known retinal disease.

Methods.: Thirty-six subjects with no history of retinal disease and with normal vision and normal intraocular pressure were enrolled in the study. Both Stratus and Spectralis OCT scanning were performed by the same operator on all subjects in one eye. Central point thickness (CPT) and retinal thickness in nine ETDRS subfields, including central subfield (CSF), were measured. Student's t-test was used to determine statistical significance.

Results.: Mean CPT, as measured by the Stratus and Spectralis OCT, was 166.9 ± 20.9 μm and 225.1 ± 17.1 μm (P < 0.0001), and mean CSF was 202.3 ± 19.6 μm and 271.4 ± 19.6 μm (P < 0.0001), respectively. Although the mean difference in CSF thickness was 69.1 μm, it ranged from 61.9 to 74 μm in the other eight ETDRS subfields.

Conclusions.: An increased measurement in retinal thickness of approximately 65 to 70 μm, as measured by Spectralis OCT compared with Stratus OCT, is consistent with the extent of axial retinal thickness measured by the two instruments. This increased measurement corresponds to the inclusion of the outer segment-RPE-Bruch's membrane complex by Spectralis OCT, which is relevant to studies using the newer SD-OCT for assessment of retinal thickness.

Optical coherence tomography (OCT) has emerged as an important imaging modality in the evaluation and management of retinal diseases. Since the late 1990s, the interpretation and management of macular pathologies, including diabetic macular edema and age-related macular degeneration (AMD), have undergone a major change with the ability of OCT to noninvasively image intraocular structures in vivo. 13  
Conventional OCT is based on the time-domain principle. Commercially available time-domain (TD) Stratus OCT (Carl Zeiss, Oberkochen, Germany) scans 400 A-scans per second, and the generated B-scan images have an axial resolution of 10 μm. However, images on Stratus OCT have poor point-to-point correlation with the clinical fundus features, and subtle retinal pathologies are missed because of inadequate sampling density. 4 In addition, the retinal pigment epithelium (RPE)-Bruch's membrane-choriocapillaris complex is not well delineated. 5 Consequently, retinal thickness includes the distance between the inner limiting membrane and the outer/inner segment junction, which appears as a low reflectivity zone. 6 The exclusion of the RPE-Bruch's membrane complex from the measurement of retinal thickness by Stratus OCT results in an underestimation. 
Spectral-domain OCT (SD-OCT), also known as Fourier-domain OCT, is a relatively new imaging technique that makes use of Fourier transformation to gather depth data from the spectra of the OCT signal and thus eliminates the need for axial translation of the reference mirror to obtain depth information. 7 The SD-OCT increases the speed of data collection by a factor of 100 (scans at 40,000 A-scans per second), resulting in improved resolution of the B-scan images and better delineation of the retinal layers, including the RPE-Bruch's membrane-choriocapillaris complex. 4,8 Hence, the retinal thickness measured by SD-OCT is inclusive of the RPE complex and should be theoretically greater than that measured by TD-OCT. 
The present study measured retinal thickness with TD-OCT (Stratus) and SD-OCT (Spectralis; Heidelberg Engineering, Heidelberg, Germany) in subjects without any known retinal disease to investigate differences in retinal thickness and to establish comparative normative data for clinical use. 
Materials and Methods
This was a prospective study comparing retinal thicknesses using Stratus and Spectralis OCT in subjects without any known retinal disease. Approval for this study was obtained from the local institutional review board. All experimental procedures adhered to the tenets of the Declaration of Helsinki, and all participants engaged in an informed consent process and signed a written consent document before study procedures were carried out. Study participants underwent complete ophthalmologic examination, including medical and family history, best-corrected visual acuity testing with ETDRS charts, applanation tonometry, slit-lamp biomicroscopy, and fundus examination. Exclusion criteria included any history or evidence of retinal disease, glaucoma, intraocular pressure >21 mm Hg, intraocular surgery or laser treatment, best-corrected visual acuity worse than 20/20, and refractive error greater than ±6.00 D. All OCTs were performed by a single experienced operator using Stratus OCT and Spectralis OCT serially. By default, data from the right eye of each subject were analyzed (except one subject in whom the quality of scan was poor in the right eye; hence, data from the left eye were analyzed). 
Stratus OCT images were generated using the fast map scan protocol consisting of six radial scans spaced 30° apart, with each scan measuring 6 mm in length (Fig. 1). Each image had a resolution of 10 μm axially and 20 μm transversally. All Stratus OCT images had a signal strength of ≥6. Retinal thickness measurements were read from the automated measurements generated by the machine using the retinal map analysis protocol. 
Figure 1.
 
Top: representative cross-sectional line scan by Stratus and Spectralis OCTs from a participant subject. GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; IS-OS, inner segment-outer segment junction; RPE, retinal pigment epithelium. Bottom: mean retinal thickness obtained in the study in the nine ETDRS subfields on Stratus and Spectralis OCTs is shown with the radii of curvature of the circles 1, 2.22, and 3.45 mm. Description of the nine ETDRS subfields, as obtained from the right eye: CSF, central subfield; SIM, superior inner macula; SOM, superior outer macula; NIM, nasal inner macula; NOM, nasal outer macula; IIM, inferior inner macula; IOM, inferior outer macula; TIM, temporal inner macula; TOM, temporal outer macula.
Figure 1.
 
Top: representative cross-sectional line scan by Stratus and Spectralis OCTs from a participant subject. GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; IS-OS, inner segment-outer segment junction; RPE, retinal pigment epithelium. Bottom: mean retinal thickness obtained in the study in the nine ETDRS subfields on Stratus and Spectralis OCTs is shown with the radii of curvature of the circles 1, 2.22, and 3.45 mm. Description of the nine ETDRS subfields, as obtained from the right eye: CSF, central subfield; SIM, superior inner macula; SOM, superior outer macula; NIM, nasal inner macula; NOM, nasal outer macula; IIM, inferior inner macula; IOM, inferior outer macula; TIM, temporal inner macula; TOM, temporal outer macula.
SD-OCT images were generated with the Spectralis OCT camera, which uses an internal fixation source and centers on the patient's fovea. The operator independently monitored the stability of fixation with incorporated infrared camera. The axial and transverse resolutions of the images were 7 μm and 10 μm, respectively. (Images were generated using the six macular radial scans, centered at the fovea at equally spaced angular orientations and 20 raster lines spaced 200 μm apart.) The quality of images was assigned a number by the machine, with numbers greater than 25 representing good quality scans. Cross-sectional images were analyzed with incorporated software. The program automatically maps the strongest two edges in each tomogram, one at the vitreoretinal interface and the other at the basement membrane of the retinal pigment epithelial-Bruch's membrane complex. Retinal thickness represents the distance between these two interfaces at each measurement point along the scan's x-axis, and the mathematical value is generated automatically. 
We selected the retinal thickness map analysis protocol on both the Spectralis SD-OCT and the Stratus TD-OCT to display numeric averages of the measurements for each of the nine subfields, as defined by the Early Treatment Diabetic Retinopathy Study. 9 Inner, intermediate, and outer rings with radii of 1.0, 2.22, and 3.45 mm, respectively, were considered for analyses. The average of all points within the inner circle of 1-mm radius was defined as central foveal subfield (CSF) thickness. The central point, which is an average of six radial scans at the foveola, was defined as the central point thickness (CPT) and was recorded for each of the subjects. 
The main parameters used for quantitative estimation of retinal thickness were CPT, CSF, and the eight other ETDRS 9 subfield segments measured at diameters of 1, 2.2, and 3.45 mm from the center of the fovea. Results were analyzed using the Student's t-test/ANOVA test (InStat, version 3.06; GraphPad, San Diego, CA) for the comparison of means and the Pearson coefficient test for the correlation studies. 
Results
Thirty-six eyes from 36 participating subjects were included in the study. Each subject underwent serial OCT scans by both Stratus OCT and Spectralis SD-OCT. Patient ages ranged from 20 to 69 years (median, 37 years). There were 23 men (63.8%) and 13 women (36.2%) in the study. 
Retinal thicknesses, both CPT and CSF as measured by the Stratus OCT and the Spectralis OCT, are shown in Table 1 for each subject. Mean CPT measured 166.9 ± 20.9 μm with Stratus OCT and 225.1 ± 17.1 μm with Spectralis OCT (P < 0.0001). Similarly, mean CSF measured 202.3 ± 19.6 μm with Stratus OCT and 271.4 ± 19.6 μm with Spectralis OCT (P < 0.0001). Mean retinal thickness in the ETDRS subfields, as measured on Stratus and Spectralis, are shown in Table 2. Mean retinal thickness was highest in the nasal outer fields in both Stratus (277.4 ± 17.2 μm) and Spectralis OCT (344.8 ± 16.5 μm). The mean difference between retinal thicknesses was 69.1 μm in the CSF measurement and 69.7 μm (range, 61.9–74.1 μm) in the other eight ETDRS subfields. Pearson correlation coefficient ranged from 0.677 to 0.884. 
Table 1.
 
Age, CPT, and CSF Measurements Obtained by Stratus and Spectralis OCT on Each Subject
Table 1.
 
Age, CPT, and CSF Measurements Obtained by Stratus and Spectralis OCT on Each Subject
Subject Age (y) CPT (μm) CSF (μm)
Stratus Spectralis Stratus Spectralis
1 24 205 229.7 231 296
2 30 150 218 201 273
3 33 155 194.7 200 263
4 26 134 218 189 280
5 23 173 249.3 198 277
6 26 179 248 210 286
7 39 191 270.2 221 298
8 37 182 242.5 241 316
9 20 155 201.2 197 259
10 37 144 212.2 164 234
11 30 190 263.3 227 311
12 28 158 188.7 190 264
13 32 149 217.7 172 245
14 31 161 225.2 187 265
15 29 157 224.8 197 278
16 29 224 223.8 232 278
17 35 176 230.7 215 286
18 29 181 235 225 276
19 27 145 213.7 184 263
20 33 136 199.3 172 243
21 28 196 227.5 229 289
22 27 160 227.5 207 287
23 35 174 237.4 215 279
24 33 171 243.7 214 292
25 42 172 225.2 209 277
26 42 142 215.7 172 247
27 44 165 225.7 209 283
28 50 143 211.2 172 241
29 56 164 220.2 191 261
30 50 167 220.3 213 250
31 48 197 227.5 218 277
32 49 146 235.7 189 266
33 54 160 217.7 197 262
34 63 166 228.5 203 272
35 69 147 213.2 179 241
36 63 193 220.2 212 255
Mean 166.9 225.1 202.3 271.4
Table 2.
 
Mean Retinal Thickness (in μm) in Each ETDRS Subfield by Stratus OCT and Spectralis OCT and the Difference between the Means
Table 2.
 
Mean Retinal Thickness (in μm) in Each ETDRS Subfield by Stratus OCT and Spectralis OCT and the Difference between the Means
CSF SIM NIM IIM TIM SOM NOM IOM TOM
Stratus 202.3 270.8 265.4 264.7 255.7 269.5 277.4 268.9 257.5
Spectralis 271.4 343.3 339.4 338.8 326.8 334.3 344.8 330.8 324.6
Difference 69.1 72.5 74 74.1 71.1 64.8 67.4 61.9 67.1
Pearson correlation coefficient 0.829 0.860 0.884 0.788 0.876 0.677 0.784 0.757 0.693
Correlation curves for the CSF as measured by Stratus OCT and Spectralis SD-OCT are represented in Figure 2; for the rest of the eight ETDRS subfields, they are represented in Figure 3
Figure 2.
 
Correlation graph showing central subfield thickness (CSF) measurements by Stratus and Spectralis OCT.
Figure 2.
 
Correlation graph showing central subfield thickness (CSF) measurements by Stratus and Spectralis OCT.
Figure 3.
 
Correlation graph showing subfield thicknesses (other than CSF) measurements by Stratus and Spectralis OCT.
Figure 3.
 
Correlation graph showing subfield thicknesses (other than CSF) measurements by Stratus and Spectralis OCT.
Discussion
Macular thickness, as measured by OCT, is one of the key outcome measures used in most clinical trials, especially those on diabetic macular edema and AMD. 10,11 Because Stratus TD-OCT was the most common commercially available OCT instrument in the past decade, most trials are designed based on Stratus OCT. Trials for diabetic retinopathy have defined CSF values >250 μm as significant for macular edema to qualify for various trials. The parameters frequently used to quantify thickness include CPT and CSF. CPT measurement on Stratus OCT is an average of six values and shows great variability because it is difficult to image the same point on the macula repeatedly. To overcome this problem, studies have defined CSF, which averages 512 values and distributes any change in location over a broader area. 12  
The introduction of commercially available Spectralis SD-OCT in the past year has revolutionized the diagnostic and prognostic significance of OCT in a number of vitreoretinal conditions such as macular edema associated with vascular occlusion, diabetic retinopathy, and AMD. 4,7,8 Quantitative and qualitative assessment using SD-OCT is particularly important in patients with AMD because it provides high-resolution images of the outer segment of the photoreceptors and the retinal pigment epithelium, a zone that is not clearly demarcated on Stratus OCT. 5 Moreover, Spectralis OCT has built-in software (Trutrack) to track eye movements; it scans the same area on the retina and increases the repeatability of measurements, thereby decreasing variability. 
One of the major differences between the TD-OCT and the SD-OCT is the axial extent of measurement in the two instruments. The Stratus TD-OCT measures retinal thickness from the internal limiting membrane to the junction of the inner and outer segments of the photoreceptors, thereby excluding some part of the outer segments and the complete RPE–Bruch's membrane–choriocapillaris complex in the measurement. The Spectralis SD-OCT, on the other hand, does include the rest of the outer segment and the RPE–Bruch's membrane–choriocapillaris complex as part of the measurement of retinal thickness. Hence, it is important to establish the correlation of retinal thickness between the two instruments. 
In the present study, with the use of Spectralis SD-OCT, the mean CSF measured 271.4 ± 19.6 μm, which was approximately 70 μm thicker than the CSF of the Stratus OCT (202.3 ± 19.6 μm). There was a high degree of correlation between the retinal thicknesses measured in the different subfields. Similarly, strong correlation has been demonstrated in studies comparing mean macular thickness on the Stratus and the Cirrus SD-OCT. In addition, the mean macular thickness on Cirrus OCT is reported to differ by 50 to 60 μm. 13,14 Although the Cirrus and the Spectralis are both SD-OCT, the Cirrus OCT measures retinal thickness up to the outer band of the RPE, whereas the Spectralis OCT includes the Bruch's membrane complex. This probably accounts for the additional 10 μm increase in the measured thickness by Spectralis OCT compared with the Cirrus OCT. 
The difference across subfield thickness was higher in the inner subfields than in the outer ones. This is consistent with the difference in the measured length of the outer segments between the foveal and extrafoveal photoreceptors in primate retina. 15 A similar difference in the macular thickness of other high-definition OCTs in healthy subjects has been reported by Legarreta et al. 13  
In the present study, within the nine ETDRS subfields, retinal thickness was thinnest within the 1-mm circle, increased in thickness at the perifoveal area (1–2.22 mm), and subsequently showed a slight decrease in the outer macular area. This was consistent with similar quantitative measurements performed on Stratus OCT. 16 In addition, retinal thickness was maximal in the nasal outer quadrant. In our study, the outer subfield thickness on Stratus OCT was higher than in previous studies on normative macular thickness. 16 This is explained by the fact that we used data from smaller radii of curvature (1, 2.22, and 3.45 mm). 
Normative data for Spectralis OCT 17 showed an average CSF thickness of 270.2 ± 22.5 μm in 50 healthy subjects. They further proposed using 320 μm as the cutoff macular thickness for any future trials using Spectralis OCT based on the mean CSF plus 2 SD. The proposed figure of 320 μm for cutoff limit is 70 μm more than the present cutoff using Stratus OCT. 
In conclusion, retinal thickness measured with the Spectralis OCT was approximately 70 μm (range, 61.9–74.1 μm) greater than the thickness of the Stratus OCT, which corresponds to the inclusion of the outer segment–RPE–Bruch's membrane–choriocapillaris complex in the measurements. This is particularly relevant and important for planning future studies using the newer high-definition OCT for assessment of macular thickness. 
Footnotes
 Supported by Foundation Fighting Blindness, Inc., Owings Mills, Maryland.
Footnotes
 Disclosure: S. Grover, None; R.K. Murthy, None; V.S. Brar, None; K.V. Chalam, None
References
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Alam S Zawadzki RJ Choi S . Clinical application of rapid serial Fourier-domain optical coherence tomography for macular imaging. Ophthalmology. 2006;113:1425–1431. [CrossRef] [PubMed]
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Sanchez-Tocino H Alvarez-Vidal A Maldonado MJ Moreno-Montanes J Garcia-Layana A . Retinal thickness study with optical coherence tomography in patients with diabetes. Invest Ophthalmol Vis Sci. 2002;43:1588–1594. [PubMed]
Wojtkowski M Srinivasan V Fujimoto JG . Three-dimensional retinal imaging with high-speed ultrahigh-resolution optical coherence tomography. Ophthalmology. 2005;112:1734–1746. [CrossRef] [PubMed]
Srinivasan VJ Wojtkowski M Witkin AJ . High-definition and 3-dimensional imaging of macular pathologies with high-speed ultrahigh-resolution optical coherence tomography. Ophthalmology. 2006;113:2054–2065. [CrossRef] [PubMed]
Early Treatment Diabetic Retinopathy Study Research Group. ETDRS report number 7: Early Treatment Diabetic Retinopathy Study design and baseline patient characteristics. Ophthalmology. 1991;98:741–756. [CrossRef] [PubMed]
Lam DS Chan CK Mohamed S . Intravitreal triamcinolone plus sequential grid laser versus triamcinolone or laser alone for treating diabetic macular edema: six-month outcomes. Ophthalmology. 2007;114:2162–2167. [CrossRef] [PubMed]
Diabetic Retinopathy Clinical Research Network Chew E Strauber S . Randomized trial of peribulbar triamcinolone acetonide with and without focal photocoagulation for mild diabetic macular edema: a pilot study. Ophthalmology. 2007;114:1190–1196. [CrossRef] [PubMed]
Diabetic Retinopathy Clinical Research Network Krzystolik MG Strauber SF . Reproducibility of macular thickness and volume using Zeiss optical coherence tomography in patients with diabetic macular edema. Ophthalmology. 2007;114:1520–1525. [CrossRef] [PubMed]
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Kakinoki M Sawada O Sawada T Kawamura H Ohji M . Comparison of macular thickness between Cirrus HD-OCT and Stratus OCT. Ophthalmic Surg Lasers Imaging. 2009;40:135–140. [CrossRef] [PubMed]
Anger EM Unterhuber A Hermann B . Ultrahigh resolution optical coherence tomography of the monkey fovea: identification of retinal sublayers by correlation with semithin histology sections. Exp Eye Res. 2004;78:1117–1125. [CrossRef] [PubMed]
Chan A Duker JS Ko TH Fujimoto JG Schuman JS . Normal macular thickness measurements in healthy eyes using Stratus optical coherence tomography. Arch Ophthalmol. 2006;124:193–198. [CrossRef] [PubMed]
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Figure 1.
 
Top: representative cross-sectional line scan by Stratus and Spectralis OCTs from a participant subject. GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; IS-OS, inner segment-outer segment junction; RPE, retinal pigment epithelium. Bottom: mean retinal thickness obtained in the study in the nine ETDRS subfields on Stratus and Spectralis OCTs is shown with the radii of curvature of the circles 1, 2.22, and 3.45 mm. Description of the nine ETDRS subfields, as obtained from the right eye: CSF, central subfield; SIM, superior inner macula; SOM, superior outer macula; NIM, nasal inner macula; NOM, nasal outer macula; IIM, inferior inner macula; IOM, inferior outer macula; TIM, temporal inner macula; TOM, temporal outer macula.
Figure 1.
 
Top: representative cross-sectional line scan by Stratus and Spectralis OCTs from a participant subject. GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; IS-OS, inner segment-outer segment junction; RPE, retinal pigment epithelium. Bottom: mean retinal thickness obtained in the study in the nine ETDRS subfields on Stratus and Spectralis OCTs is shown with the radii of curvature of the circles 1, 2.22, and 3.45 mm. Description of the nine ETDRS subfields, as obtained from the right eye: CSF, central subfield; SIM, superior inner macula; SOM, superior outer macula; NIM, nasal inner macula; NOM, nasal outer macula; IIM, inferior inner macula; IOM, inferior outer macula; TIM, temporal inner macula; TOM, temporal outer macula.
Figure 2.
 
Correlation graph showing central subfield thickness (CSF) measurements by Stratus and Spectralis OCT.
Figure 2.
 
Correlation graph showing central subfield thickness (CSF) measurements by Stratus and Spectralis OCT.
Figure 3.
 
Correlation graph showing subfield thicknesses (other than CSF) measurements by Stratus and Spectralis OCT.
Figure 3.
 
Correlation graph showing subfield thicknesses (other than CSF) measurements by Stratus and Spectralis OCT.
Table 1.
 
Age, CPT, and CSF Measurements Obtained by Stratus and Spectralis OCT on Each Subject
Table 1.
 
Age, CPT, and CSF Measurements Obtained by Stratus and Spectralis OCT on Each Subject
Subject Age (y) CPT (μm) CSF (μm)
Stratus Spectralis Stratus Spectralis
1 24 205 229.7 231 296
2 30 150 218 201 273
3 33 155 194.7 200 263
4 26 134 218 189 280
5 23 173 249.3 198 277
6 26 179 248 210 286
7 39 191 270.2 221 298
8 37 182 242.5 241 316
9 20 155 201.2 197 259
10 37 144 212.2 164 234
11 30 190 263.3 227 311
12 28 158 188.7 190 264
13 32 149 217.7 172 245
14 31 161 225.2 187 265
15 29 157 224.8 197 278
16 29 224 223.8 232 278
17 35 176 230.7 215 286
18 29 181 235 225 276
19 27 145 213.7 184 263
20 33 136 199.3 172 243
21 28 196 227.5 229 289
22 27 160 227.5 207 287
23 35 174 237.4 215 279
24 33 171 243.7 214 292
25 42 172 225.2 209 277
26 42 142 215.7 172 247
27 44 165 225.7 209 283
28 50 143 211.2 172 241
29 56 164 220.2 191 261
30 50 167 220.3 213 250
31 48 197 227.5 218 277
32 49 146 235.7 189 266
33 54 160 217.7 197 262
34 63 166 228.5 203 272
35 69 147 213.2 179 241
36 63 193 220.2 212 255
Mean 166.9 225.1 202.3 271.4
Table 2.
 
Mean Retinal Thickness (in μm) in Each ETDRS Subfield by Stratus OCT and Spectralis OCT and the Difference between the Means
Table 2.
 
Mean Retinal Thickness (in μm) in Each ETDRS Subfield by Stratus OCT and Spectralis OCT and the Difference between the Means
CSF SIM NIM IIM TIM SOM NOM IOM TOM
Stratus 202.3 270.8 265.4 264.7 255.7 269.5 277.4 268.9 257.5
Spectralis 271.4 343.3 339.4 338.8 326.8 334.3 344.8 330.8 324.6
Difference 69.1 72.5 74 74.1 71.1 64.8 67.4 61.9 67.1
Pearson correlation coefficient 0.829 0.860 0.884 0.788 0.876 0.677 0.784 0.757 0.693
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