April 2012
Volume 53, Issue 4
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Glaucoma  |   April 2012
Imaging of the Iridocorneal Angle with the RTVue Spectral Domain Optical Coherence Tomography
Author Affiliations & Notes
  • Shamira A. Perera
    From the Singapore National Eye Centre, Singapore and Singapore Eye Research Institute, Singapore;
  • Ching Lin Ho
    From the Singapore National Eye Centre, Singapore and Singapore Eye Research Institute, Singapore;
  • Tin Aung
    From the Singapore National Eye Centre, Singapore and Singapore Eye Research Institute, Singapore;
    the Yong Loo Lin School of Medicine, National University of Singapore, Singapore;
  • Mani Baskaran
    From the Singapore National Eye Centre, Singapore and Singapore Eye Research Institute, Singapore;
  • Henrietta Ho
    From the Singapore National Eye Centre, Singapore and Singapore Eye Research Institute, Singapore;
  • Tin A. Tun
    From the Singapore National Eye Centre, Singapore and Singapore Eye Research Institute, Singapore;
  • Tian Loon Lee
    From the Singapore National Eye Centre, Singapore and Singapore Eye Research Institute, Singapore;
  • Rajesh S. Kumar
    From the Singapore National Eye Centre, Singapore and Singapore Eye Research Institute, Singapore;
    and Narayana Nethralaya, Bangalore, India.
  • Corresponding author: Shamira Perera, Glaucoma Service, Singapore National Eye Centre, 11 Third Hospital Avenue, Singapore 168751; shamiraperera@hotmail.com
Investigative Ophthalmology & Visual Science April 2012, Vol.53, 1710-1713. doi:10.1167/iovs.11-8159
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      Shamira A. Perera, Ching Lin Ho, Tin Aung, Mani Baskaran, Henrietta Ho, Tin A. Tun, Tian Loon Lee, Rajesh S. Kumar; Imaging of the Iridocorneal Angle with the RTVue Spectral Domain Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2012;53(4):1710-1713. doi: 10.1167/iovs.11-8159.

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

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Abstract

Purpose.: To determine the ability of the RTVue spectral domain optical coherence tomography (SDOCT) to image the anterior chamber angle (ACA).

Methods.: Consecutive subjects, recruited from glaucoma clinics, prospectively underwent ophthalmic evaluation including gonioscopy by an ophthalmologist and anterior chamber imaging with SDOCT, adapted with a corneal lens adapter (cornea anterior module–low magnification [CAM-L]) and anterior segment OCT (ASOCT), both performed by a technician. Two different ophthalmologists, masked to gonioscopy findings, assessed visualization of the scleral spur (SS), Schwalbe's line (SL), and trabecular meshwork (TM) by the two modalities. The ability to detect a closed angle was compared with gonioscopy.

Results.: The average age (SD) of the 81 subjects enrolled was 64.1 (11.4) years; the majority were Chinese (91.4%) and female (61.7%). SDOCT images revealed the SS in 26.9% (56/324) of quadrants and the SL in 44.1% (143/324) of quadrants; in ASOCT images, the SS could be visualized in 69.1% (224/324) of quadrants (P < 0.0001), but the SL was undetectable. The TM was detected equally well (17.3%, P < 0.92) using either device. The angle status was gradable in only 41.7% images with SDOCT, compared with 71.3% of ASOCT images (P < 0.0001). ACA was classified as closed in 19.3% of quadrants (26/135) with SDOCT images and in 44.2% (102/231) with ASOCT images compared with 37.7% (122/324) on gonioscopy. When analyzing the horizontal quadrants only, both modalities agreed well with gonioscopy, 0.75 and 0.74, respectively (AC1 statistics).

Conclusions.: The RTVue SDOCT allowed visualization of SL, TM, and SS. However, these landmarks were not detected in a large percentage of images.

Introduction
Primary angle closure glaucoma (PACG) is a major form of glaucoma in Asia. 13 The anterior segment optical coherence tomography (ASOCT), a time domain OCT device, was introduced to image the anterior segment. Using a wavelength of 1310 nm, ASOCT allows good visualization of the anterior chamber angle (ACA). 4 However, a potential limitation of the ASOCT for detecting iridocorneal contact/closed angles is that detailed and consistent imaging of the trabecular meshwork (TM) is poor. The diagnosis of a closed angle is thus based on identifying contact between the iris and the angle wall anterior to the scleral spur (SS), which is a more posteriorly placed structure than the TM. The SS is used as a surrogate landmark instead of the TM as it is more easily visible on ASOCT imaging. However, a recent study reported that even the SS can only be detected in 70% to 80% of angle images, thus limiting the practicality of the device. 5 Comparative studies between gonioscopy and ASOCT have shown higher rates of detection of closed angles with ASOCT. This finding may be due to ASOCT imaging being under completely dark conditions, artifactual opening of the angle by gonioscopy, or a discrepancy in the definitions of closed angles between the two examination methods. 6,7  
The use of Fourier domain or spectral domain OCT (SDOCT) for retinal and corneal imaging has been gaining interest recently. 810 SDOCT provides real-time imaging with a higher axial resolution and a scan rate that is 50 to 60 times faster than time-domain OCT devices, thereby limiting movement artifact.10 With gonioscopy as the reference standard, a recent study reported on the diagnostic capability of one SDOCT device (Cirrus, Carl Zeiss Meditec, Dublin, CA) versus a time-domain ASOCT device at detecting closed angles. The sensitivity and specificity for the Cirrus were 64.7% and 96.4%, respectively, while the ASOCT demonstrated a sensitivity of 88.9% and specificity of 71.4%. 11 Another study has shown that a different SDOCT, RTVue (Optovue, Fremont, CA), has good reproducibility and good agreement with gonioscopy, indicating potential for future clinical use. 12  
The aim of this study was to assess the ability of the RTVue SDOCT device for imaging ACA structures, and for diagnosing closed angles in a clinical setting, using gonioscopy as the reference standard. We also compared the performance of this device with ASOCT. 
Methods
Consecutive subjects were recruited from the glaucoma clinics of Singapore National Eye Centre in Singapore. Written informed consent was obtained from all subjects and the study was approved by the institutional research review board and was conducted in accordance with the tenets of the Declaration of Helsinki. All subjects underwent detailed ophthalmic examination, including slit lamp biomicroscopy, gonioscopy, and anterior segment imaging, on the same day. Exclusion criteria included eyes with a history of intraocular surgery, penetrating trauma, or any corneal or media abnormalities that impeded angle imaging. Subjects who had had laser iridotomy were not excluded. 
Gonioscopy
A single glaucoma specialty-trained ophthalmologist (CLH) performed gonioscopy in all participants; gonioscopy was performed with a Sussman 4 mirror lens (Ocular Instruments, Bellevue, WA). This examination was performed in the dark using a 1-mm light beam which was reduced to a narrow slit, offset horizontally and vertically for nasal and temporal angle viewing. All four quadrants were viewed with the eye in the primary gaze position. The examiner ensured that light did not fall on the pupil during the test and avoided any inadvertent pressure on the globe that would artificially open the angle. The angle was graded using the modified Shaffer's grading system. 13 An angle was defined as closed in a quadrant if the posterior TM was not visible on nonindentation gonioscopy. 
Anterior Segment Imaging
Both the ASOCT (Visante, Carl Zeiss Meditec) and SDOCT (RTVue, Optovue) imaging studies were performed by a single trained technician (TAT) masked to clinical and gonioscopy findings. All four quadrants (superior, inferior, nasal, and temporal) were imaged separately in the dark. The upper and lower lids were manipulated away to visualize the superior and inferior angles, respectively, whilst avoiding pressure on the globe. Both devices utilized an external fixation target to direct the subject's gaze. 
The ASOCT device allows rapid image acquisition of 2000 A scans per second, transverse resolution of 60 μm, and axial resolution of 10 to 20 μm. 14 Images of the ACA were acquired using the high-resolution corneal scan mode; this mode has a scan length of 10 mm and depth of 3 mm. 
The SDOCT allows 26,000 A scans per second, a transverse resolution of 15 μm, and axial resolution of 5 μm. 14 The RTVue used in this study had a corneal lens adapter (cornea anterior module–low magnification [CAM-L]), fixed in front of the ocular lens, that helps to image the cornea and anterior chamber of the eye. The CAM-L provides a scan length of 2 to 6 mm and an image size of 12 × 8 mm. The working distance between the lens adapter and cornea was 13 mm on the CAM-L model. The angle scan mode was used for imaging that provides a 3-mm scan length and a scan depth of 2.3 mm. 
Image Analysis
Two trained glaucoma specialists (RSK and MB) masked to other test results sat together and examined all SDOCT and ASOCT images; images from each of these modalities were randomly assorted and graded at two separate sessions. Attempts were made to identify the following structures in angle images from both devices: SS, Schwalbe's line (SL), and TM. SL was defined as the point of termination of Descemet's membrane, while the TM was identified as a triangular low signal area between SL and the SS. The SS was defined as a point where a change in the curvature of the inner surface of the angle wall was noted, usually appearing as an inward protrusion of the sclera. 5 A closed angle in a quadrant was diagnosed by the presence of contact between the iris and angle wall anterior to the SS. Where the SS was not visible, the TM, if visible, was used as a surrogate landmark; a closed angle in a quadrant was then diagnosed by any contact between the iris and the TM in that quadrant. 
Statistical Analysis
The sample size calculation was based on comparison of sensitivities for matched groups in a diagnostic study. With an estimated sensitivity of 89% for angle closure detection using ASOCT in comparison to gonioscopy, the number of subjects required was 69 in this study with 80% power and an α of 0.05. If both eyes fulfilled the inclusion criteria, the right eye was chosen for analysis. Continuous variables were compared with either parametric or nonparametric tests according to data distribution. Categorical data were analyzed using the χ 2 test. Statistical analysis was performed using MedCalc software (Version 9.4.2.0, MedCalc, Mariakerke, Belgium). Agreement between the two devices and gonioscopy was assessed using AC1 statistics. 15 The AC1 statistic is similar to the κ statistic as a measure of agreement. The formula is essentially identical, but the probability of agreement by chance is calculated by a different method. The κ statistic is used in situations where one of the “agreed-category” has a small percentage, while the other “agreed-category” is much larger. In all cases a P value of <0.05 was considered statistically significant. 
Results
Eighty-one subjects (81 eyes) were enrolled. The mean (SD) age of the participants was 61.4 (11.4) years, and the majority of subjects were female (61.7%) and Chinese (91.4%). 
The SS was identifiable in 97 of 324 quadrants of SDOCT images (29.9%), but much more often in the ASOCT images: 224/324 quadrants (69.1%; P < 0.0001) (Table 1). This difference in SS visualization was statistically significant for each quadrant (Table 2). Furthermore, detection of the SS was better for the horizontal meridians compared with the vertical meridians (P < 0.0001). SL was identified in 143/324 quadrants (44.1%) with SDOCT yet could not be seen in any of the ASOCT images (P < 0.0001) (Table 1). Similarly, a quadrant-wise analysis of SDOCT images showed that SL was detected in the horizontal meridians more often than the vertical meridians (P < 0.0001) (Table 3). It was possible to image the TM in 56 of 324 (17.3%) quadrants using both devices (P = 0.95). Again, images from both devices demonstrated greater visibility of TM in the horizontal quadrants (P < 0.0001) (Table 1). 
Table 1.
 
Comparison of ACA Landmark Visibility in SDOCT and ASOCT Images
Table 1.
 
Comparison of ACA Landmark Visibility in SDOCT and ASOCT Images
Landmark SDOCT n (%) ASOCT n (%) P Value
Schwalbe's line 143 (44.1) 0 <0.00001
Scleral spur 87 (26.9) 224 (69.1) <0.0001
Trabecular meshwork 56 (17.3) 56 (17.3) 0.95
Table 2.
 
Number of Quadrants with Detectable Scleral Spur in SDOCT and ASOCT Images (324 Quadrants)
Table 2.
 
Number of Quadrants with Detectable Scleral Spur in SDOCT and ASOCT Images (324 Quadrants)
Quadrant SDOCT n (%) ASOCT n (%) P Value
Inferior 17 (20.9) 32 (39.6) 0.02
Superior 8 (9.9) 57 (70.3) <0.0001
Nasal 36 (44.4) 67 (82.7) <0.0001
Temporal 36 (44.4) 68 (83.9) <0.0001
Total 97 (29.9) 224 (69.1) <0.0001
Table 3.
 
Quadrant-Wise Visibility of ACA Structures Visibility in SDOCT Images (n = 324 Quadrants)
Table 3.
 
Quadrant-Wise Visibility of ACA Structures Visibility in SDOCT Images (n = 324 Quadrants)
Quadrant Schwalbe's Line Visible n (%) Scleral Spur Visible n (%) Trabecular Meshwork n (%)
Inferior 21 (25.9) 17 (20.9) 5 (6.2)
Superior 18 (22.2) 8 (9.9) 2 (2.5)
Nasal 59 (72.8) 36 (44.4) 24 (29.6)
Temporal 45 (55.6) 36 (44.4) 25 (30.9)
Total 143 (44.1) 87 (26.9) 56 (17.3)
Comparing the percentage of images from each device where a decision could be made on the angle status, only 143 of 324 (44.1%) images from SDOCT were gradable for assessment of closed angle status in a particular quadrant, compared with 224/324 (69.1%) images from ASOCT (P < 0.0001). Imaging of the vertical meridians fared worse than the horizontal meridians. Far fewer of the SDOCT images taken along the vertical meridians were gradable compared with ASOCT; 22.1% vs. 69.8%, respectively (P < 0.0001). This difference was not significant for images from the horizontal meridians for each device (61.1% for SDOCT and 72.8% for ASOCT; P = 0.58). 
A closed angle was noted in 122 of 324 quadrants (37.7%) on gonioscopy. None of the eyes had peripheral anterior synechiae. In comparison, only 19.3% of quadrants were graded as having closed angles on SDOCT images compared with 44.2% on ASOCT images. Table 4 shows quadrant-wise comparison of angle status determined by the two devices and gonioscopy. There was a statistically significant difference in detection of closed angles in the horizontal meridians between SDOCT and gonioscopy, but not in the vertical meridians. Only when the superior quadrant was analyzed alone, was the detection of closed angles similar between all three modalities. 
Table 4.
 
Number of ACA Quadrants That Appeared Closed on Gradable Images Using SDOCT and ASOCT Compared with Gonioscopy (81 Eyes)
Table 4.
 
Number of ACA Quadrants That Appeared Closed on Gradable Images Using SDOCT and ASOCT Compared with Gonioscopy (81 Eyes)
Quadrant No. Closed on SDOCT (A) n (%) No. Closed on ASOCT (B) n (%) No. Closed on Gonioscopy (C) n (%) P Value
Inferior 7 (35.0) 40 (75.5) 18 (22.2) 0.003 (A and B)
0.36 (A and C)
<0.0001 (B and C)
Superior 6 (37.5) 34 (56.7) 49 (60.5) 0.28 (A and B)
0.16 (A and C)
0.78 (B and C)
Nasal 8 (14.8) 19 (31.7) 29 (35.8) 0.06 (A and B)
0.0005 (A and C)
0.74 (B and C)
Temporal 5 (11.1) 9 (15.5) 26 (32.1) 0.72 (A and B)
0.02 (A and C)
0.04 (B and C)
Total 26 (19.3) 102 (44.2) 122 (37.7) <0.0001 (A and B)
0.0002 (A and C)
0.14 (B and C)
We used only the horizontal meridians from both devices to determine agreement with gonioscopy, since there were only 12 vertical quadrants that were gradable from the SDOCT images. The agreement between the two devices and gonioscopy for two quadrants of closed angles was good; 0.75 for SDOCT and 0.74 for ASOCT (AC1 statistics). To keep in line with the previously used and well-accepted definitions of an eye displaying angle closure (i.e., having at least 180° out of 360° of closed angle), we used a similar endpoint of having one out of two quadrants closed as we only examined the horizontal two quadrants. If having one quadrant out of two was used to define an eye as angle closure, the agreement was poorer with AC1 statistics of 0.60 (SDOCT) and 0.57 (ASOCT). Five eyes that were determined to have two quadrants closed on gonioscopy were found to have two open angles on SDOCT (P = 0.87); similarly, ASOCT incorrectly classified eight eyes that were closed on gonioscopy as open (P = 0.77). 
Discussion
The RTVue SDOCT with the corneal lens module attachment demonstrated poor to average detection of the SS, as judged against the ASOCT (26.9% vs. 69.1%, respectively). The SS is the key landmark for quantitative and qualitative angle assessment. Its major advantage in this study over the ASOCT was in its unique ability to detect the SL in 44.1% of subjects. In contrast, Wong et al. report in vivo visualization of the SS in almost 80% and of the SL in approximately 90% of quadrants with the use of another SDOCT device, the Cirrus. 11 The difference between the Cirrus and the RTVue in the ability to detect ACA landmarks in the two studies could be due to a number of factors. 11 First, an RTVue image is the product of 16 processed and averaged images, while the Cirrus (and the ASOCT for that matter) is a single-frame image. Alternatively, differing proprietary methods of reducing signal-to-noise ratios could be to blame. It could be technician related; however, the single technician who performed the imaging in this study has extensive experience with all manner of anterior segment imaging devices. The most important factor to consider is the motion artifact caused by ocular movements that may lead to an indistinct image depending on the scan time. The use of an external fixation target for directing the subject's gaze cannot be standardized, and the images acquired might not have been centered similarly in all instances, leading to edge artifact and unclear images. There are also two good methodological reasons why the two SDOCT studies have different detection rates for the angle structures. Wong et al. have smaller numbers and only look at the more easily visible horizontal meridians. In that study, 17/90 (18.8%) have one angle closed. In our study, 122/324 (37.7%) had one angle closed. It is therefore unsurprising that the detection of SL and the TM may have been more difficult when more subjects with closed angles were included in the case mix. 
Wylegala et al. image 54 eyes using the RTVue and the Visante ASOCT and analyze them both qualitatively and quantitatively. 12 They report good correlation between anterior segment parameters, including central corneal thickness, trabecular iris angle, and angle opening distance. They also report that all anterior chamber angle structures (SS, TM, and Schlemm's canal) are visible with the RTVue; however, they do not state if they achieve this in all images or how many images have poor visibility of the ACA structures. 
The depth and width of view provided by SDOCT does not allow imaging of the entire angle up to the iris root; hence the entire angle cannot be viewed in a single image as in the ASOCT. Gonioscopy can be used to assess the entire circumference of the angle, whereas these imaging devices only deliver a cross-sectional view of the angle. A subject with a gonioscopically predominantly closed angle in a quadrant with a small open segment would have been erroneously classified as open if that meridian were chosen for imaging. In addition, angle features such as peripheral anterior synechiae, iris strands, and pigment cannot be determined. There is also an inherent limitation in currently available ASOCT devices for imaging vertical quadrants. This is due to poorer rates of detection of the SS in images obtained in the superior and inferior quadrants compared with images of the horizontal quadrants. 5  
We found that the agreement between the two devices and gonioscopy was moderate when only one quadrant out of two was used to define closed angles; however, this result should be interpreted with caution since only 35 eyes imaged by the SDOCT and 56 imaged by the ASOCT were analyzed. This was because only the horizontal meridians were used for determining agreement. Although this is a commonly used and time-saving protocol for anterior segment imaging, it must be remembered that this is not a complete four-quadrant scan, which would be the ideal approach to decide the status of the angle in an eye. Furthermore, the CAM-L module is an optional attachment for the RTVue, produced by the same manufacturer. It is possible that a fully integrated device may work better in practice. Our cited value of 0.60 using AC1 statistics for agreement between RTVue and gonioscopy compares favorably with the κ = 0.63 between Cirrus and gonioscopy calculated by Wong et al.11  
This study has a few limitations. As stated earlier, the angle imaging was performed by directing the subject's gaze using an external fixation light to center the iridocorneal angle in the instrument's field of view. This might have led to inadequate image centration in the SDOCT in contrast to the ASOCT, which has an external fixation device incorporated. We used a 3-mm scan length as recommended by the manufacturer while imaging the angle with the SDOCT; however, we do not know if the 6-mm scan would provide more useful information about the same area. Since a single observer performed the gonioscopy, there could have been a systematic bias in the angle grading. In addition, differences in testing conditions exist for gonioscopy and for the imaging devices. 
The imaging devices use infrared light and do not require contact with the eye. Inadvertent indentation might have occurred during gonioscopy despite efforts to avoid this. Similarly, even though ambient light is kept to a minimum during gonioscopy, the light may have led to a marginal degree of pupil constriction and angle opening. Hence, gonioscopy may have missed eyes with irido-angle contact. The height of irido-angle contact used to define a closed angle is also different with each technique. With imaging devices like the SDOCT and ASOCT, a closed angle is defined as any contact between the iris and angle wall anterior to the SS, but if this contact did not occur up to the level of the TM, the angle would have been graded as open on gonioscopy. Thus, it is also possible that imaging may have overdetected eyes with closed angles leading to more false positives. In images where the SS was not detected, an angle with any contact between the TM (when identified) and the iris was considered closed. This inconsistency of definitions used for closed angles would not only impact the incomparability of alternative SDOCT devices at detecting angle closure compared with the RTVue but also would mean a more lenient definition of closed angles had been used for the SDOCT device. Regarding the SDOCT images, excluding the large number of poor quality scans would have made it more difficult for the device to detect the true closed quadrants from an already low potential of 122/324 quadrants available on gonioscopy. Reproducibility of detection is important, especially for difficult-to-detect structures. However, the reproducibility of the RTVue at detecting structures such as Schlemm's canal was not measured in this study. In a separate study using AC1 statistics, we found the inter-observer agreement for identification of the Schlemm's canal using the iVue (Optovue) varied from 0.522 to 0.970 depending on the quadrant investigated, indicating significant variability (Quek, Tun, Narayanaswamy, et al. unpublished data, 2011). The iVue is an equivalent, more compact version of the RTVue device, from the same manufacturer, which has integrated anterior and posterior segment scanning capabilities. 
In summary, the RTVue SDOCT device was found to have limited ability to image angle structures such as the TM, SS, and SL. This made assessment of angle closure status impossible in about 60% of angle quadrants. For quadrants in which closed angles could be assessed, there was moderate agreement with gonioscopy. 
References
Foster PJ Oen FT Machin D . The prevalence of glaucoma in Chinese residents of Singapore: a cross-sectional population survey of the Tanjong Pagar district. Arch Ophthalmol . 2000;118:1105–1111. [CrossRef] [PubMed]
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Mumcuoglu T Wollstein G Wojtkowski M . Improved visualization of glaucomatous retinal damage using high-speed ultrahigh-resolution optical coherence tomography. Ophthalmology . 2008;115:784–791. [CrossRef]
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Wylegala E Teper S Nowinska AK . Anterior segment imaging: Fourier-domain optical coherence tomography versus time-domain optical coherence tomography. J Cataract Refract Surg . 2009;35:1410–1414. [CrossRef] [PubMed]
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Footnotes
 Supported by grants from the National Research Foundation and the National Medical Research Council, Singapore.
Footnotes
 Disclosure: S.A. Perera, Carl Zeiss Meditec (R); C. Lin, None; T. Aung, Carl Zeiss Meditec (F, R); M. Baskaran, None; H. Ho, None; T.A. Tun, None; T.L. Lee, None; R.S. Kumar, None
Table 1.
 
Comparison of ACA Landmark Visibility in SDOCT and ASOCT Images
Table 1.
 
Comparison of ACA Landmark Visibility in SDOCT and ASOCT Images
Landmark SDOCT n (%) ASOCT n (%) P Value
Schwalbe's line 143 (44.1) 0 <0.00001
Scleral spur 87 (26.9) 224 (69.1) <0.0001
Trabecular meshwork 56 (17.3) 56 (17.3) 0.95
Table 2.
 
Number of Quadrants with Detectable Scleral Spur in SDOCT and ASOCT Images (324 Quadrants)
Table 2.
 
Number of Quadrants with Detectable Scleral Spur in SDOCT and ASOCT Images (324 Quadrants)
Quadrant SDOCT n (%) ASOCT n (%) P Value
Inferior 17 (20.9) 32 (39.6) 0.02
Superior 8 (9.9) 57 (70.3) <0.0001
Nasal 36 (44.4) 67 (82.7) <0.0001
Temporal 36 (44.4) 68 (83.9) <0.0001
Total 97 (29.9) 224 (69.1) <0.0001
Table 3.
 
Quadrant-Wise Visibility of ACA Structures Visibility in SDOCT Images (n = 324 Quadrants)
Table 3.
 
Quadrant-Wise Visibility of ACA Structures Visibility in SDOCT Images (n = 324 Quadrants)
Quadrant Schwalbe's Line Visible n (%) Scleral Spur Visible n (%) Trabecular Meshwork n (%)
Inferior 21 (25.9) 17 (20.9) 5 (6.2)
Superior 18 (22.2) 8 (9.9) 2 (2.5)
Nasal 59 (72.8) 36 (44.4) 24 (29.6)
Temporal 45 (55.6) 36 (44.4) 25 (30.9)
Total 143 (44.1) 87 (26.9) 56 (17.3)
Table 4.
 
Number of ACA Quadrants That Appeared Closed on Gradable Images Using SDOCT and ASOCT Compared with Gonioscopy (81 Eyes)
Table 4.
 
Number of ACA Quadrants That Appeared Closed on Gradable Images Using SDOCT and ASOCT Compared with Gonioscopy (81 Eyes)
Quadrant No. Closed on SDOCT (A) n (%) No. Closed on ASOCT (B) n (%) No. Closed on Gonioscopy (C) n (%) P Value
Inferior 7 (35.0) 40 (75.5) 18 (22.2) 0.003 (A and B)
0.36 (A and C)
<0.0001 (B and C)
Superior 6 (37.5) 34 (56.7) 49 (60.5) 0.28 (A and B)
0.16 (A and C)
0.78 (B and C)
Nasal 8 (14.8) 19 (31.7) 29 (35.8) 0.06 (A and B)
0.0005 (A and C)
0.74 (B and C)
Temporal 5 (11.1) 9 (15.5) 26 (32.1) 0.72 (A and B)
0.02 (A and C)
0.04 (B and C)
Total 26 (19.3) 102 (44.2) 122 (37.7) <0.0001 (A and B)
0.0002 (A and C)
0.14 (B and C)
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