Carol Yim Lui Cheung

The Chinese University of Hong Kong, Hong Kong, Hong Kong

Are you Carol Yim Lui Cheung?

Claim your profile

Publications (20)56.33 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we present an unsupervised framework using domain priors extracted from the primary structures of the optic nerve head for automated optic cup localization. Our approach provides 3 major contributions. First, we identify a new domain prior, optic cup origin. This prior is derived from the physiological understanding that the central retinal vessels traces its origin from the optic cup before extending to the rest of the retinal. Second, we propose extracting the features of the optic nerve head from superpixels, which are obtained from low-level grouping and have more natural and descriptive features than pixel based techniques. Third, the domain knowledge comprising of optic cup origin and cup pallor, and the extracted features from superpixels are then used to drive a similarity-based label propagation and refinement scheme for the optic cup localization. Our approach was validated on a clinical online dataset, ORIGA-light, of 650 population-based images. Overall, our approach is able to achieve a 32.2% nonoverlap ratio (m1), a 33.8% relative absolute area difference (m2) and a 10.6% absolute CDR error (δ).
    Biomedical Imaging (ISBI), 2013 IEEE 10th International Symposium on; 01/2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: The vertical Cup-to-Disc Ratio (CDR) is an important indicator in the diagnosis of glaucoma. Automatic segmentation of the optic disc (OD) and optic cup is crucial towards a good computer-aided diagnosis (CAD) system. This paper presents a statistical model-based method for the segmentation of the optic disc and optic cup from digital color fundus images. The method combines knowledge-based Circular Hough Transform and a novel optimal channel selection for segmentation of the OD. Moreover, we extended the method to optic cup segmentation, which is a more challenging task. The system was tested on a dataset of 325 images. The average Dice coefficient for the disc and cup segmentation is 0.92 and 0.81 respectively, which improves significantly over existing methods. The proposed method has a mean absolute CDR error of 0.10, which outperforms existing methods. The results are promising and thus demonstrate a good potential for this method to be used in a mass screening CAD system.
    Computer-Based Medical Systems (CBMS), 2012 25th International Symposium on; 01/2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: Identifying the boundary of the optic cup excavation is of critical importance in the assessment of glaucomatous risk. Currently, most approaches are focused on the use of pallor. We present an automatic method to determine the cup excavation boundary based on vessel kinking in non-stereo retinal fundus images. The method tracks vessels using a self-initialized evolving model which adapts during propagation. A piecewise analysis of the vessel trajectory is conducted to determine vessel kinking locations, from which the optic cup is obtained. Our proposed method is validated on a large database of 618 images. The results suggest that our proposed method is able to obtain a more accurate cup excavation detection than other tested methods.
    Pattern Recognition (ICPR), 2012 21st International Conference on; 01/2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: To compare the performance of standard automated perimetry (SAP), frequency-doubling technology (FDT) perimetry, and short-wavelength automated perimetry (SWAP) in detecting glaucoma. One hundred thirty-two eyes of 95 glaucoma patients and 37 normal subjects had retinal nerve fiber layer (RNFL) imaging and visual field testing by SAP, Matrix FDT perimetry, and Swedish interactive thresholding algorithm (SITA) SWAP at the same visit (all perimeters by Carl Zeiss Meditec, Inc., Dublin, CA). Visual field defects were confirmed with two or more consecutive examinations by the same types of perimetry. Glaucoma was defined with the reference to the RNFL thickness deviation map score (≥ 4, glaucomatous; ≤ 2, normal). The sensitivity, specificity, and area under the receiver operating characteristic curve (AUC) of MD (mean deviation) and PSD (pattern standard deviation) of the perimetries were compared. Taking all glaucoma patients into consideration, the sensitivity was highest for Matrix FDT perimetry (69%), followed by SAP (68%), and then SITA SWAP (59%). When the analysis included only patients with early glaucoma, the sensitivity decreased to 52%, 46%, and 34%, respectively, with a significant difference detected between Matrix FDT perimetry and SITA SWAP (P = 0.034). The specificity was ≥ 97% for all perimetries. The AUCs of MD and PSD followed a similar order, with Matrix FDT perimetry having the greatest AUC (0.89-0.94), followed by SAP (0.87-0.94), and then SITA SWAP (0.69-0.90). There were significant differences in sensitivities at 90% specificity between Matrix FDT perimetry and SITA SWAP (P ≤ 0.005 for MD; P ≤ 0.039 for PSD). The performance for glaucoma detection was comparable between FDT perimetry and SAP. FDT perimetry had a higher sensitivity for detecting glaucoma than did SWAP at a comparable level of specificity.
    Investigative ophthalmology & visual science 08/2011; 52(10):7325-31. · 3.43 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate the performance of progression detection and the rate of change of retinal nerve fiber layer (RNFL), neuroretinal rim, and visual field measurements in glaucoma. Prospective study. One hundred eight eyes of 70 glaucoma patients. Patients were followed up every 4 months for at least 2.9 years (median, 3.2 years) for measurement of RNFL thickness with the Stratus optical coherence tomograph (OCT) (Carl Zeiss Meditec, Dublin, CA), neuroretinal rim area with the Heidelberg Retinal Tomograph (HRT 3; Heidelberg Engineering, GmbH, Dossenheim, Germany), and visual field with the Humphrey Field Analyzer II (Carl Zeiss Meditec). Linear regression analyses were performed between visual field index (VFI), RNFL, and neuroretinal rim measurements and age, with progression defined when a significant negative trend was detected. The agreement among structural and functional measurements was evaluated with κ statistics. The mean rate of change was estimated with linear mixed modeling. The agreement on progression detection and the rate of change of RNFL, neuroretinal rim, and VFI measurements. A total of 1105 OCT, 1062 HRT, and 1099 visual field measurements were analyzed. The agreement of progression detection among the 3 investigations was poor (κ≤0.09). Ten eyes (9.3%; 9 patients) showed progression by average RNFL thickness, 16 (14.8%; 14 patients) by global neuroretinal rim area, and 35 (32.4%; 31 patients) by VFI. Only 1 eye (0.9%) had progression detected by all 3 methods. There were large variations in the rate of change of VFI, average RNFL thickness, and global neuroretinal rim area, with a range between -0.63% and -4.97% per year, -2.32% and -10.12% per year, and -0.61% and -8.48% per year, respectively. The respective mean rate estimates were -1.15% per year (95% confidence interval [CI], -1.56% to -0.73%), -0.70% per year (95% CI, -1.19% to -0.21%), and -1.06% per year (95% CI, -1.56% to -0.55%). The agreement of progression detection among RNFL, neuroretinal rim, and visual field measurements was poor, and the rate of RNFL, neuroretinal rim, and visual field progression varied considerably within and between subjects. Given this variability, interpretation of RNFL, neuroretinal rim, and VFI progression always should be evaluated on an individual basis. Proprietary or commercial disclosure may be found after the references.
    Ophthalmology 04/2011; 118(8):1551-7. · 5.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Under the framework of computer-aided diagnosis, optical coherence tomography (OCT) has become an established ocular imaging technique that can be used in glaucoma diagnosis by measuring the retinal nerve fiber layer thickness. This letter presents an automated retinal layer segmentation technique for OCT images. In the proposed technique, an OCT image is first cut into multiple vessel and nonvessel sections by the retinal blood vessels that are detected through an iterative polynomial smoothing procedure. The nonvessel sections are then filtered by a bilateral filter and a median filter that suppress the local image noise but keep the global image variation across the retinal layer boundary. Finally, the layer boundaries of the filtered nonvessel sections are detected, which are further classified to different retinal layers to determine the complete retinal layer boundaries. Experiments over OCT for four subjects show that the proposed technique segments an OCT image into five layers accurately.
    IEEE Transactions on Biomedical Engineering 11/2010; · 2.35 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate and compare the diagnostic agreement and performance for glaucoma detection between a confocal scanning laser ophthalmoscope and a spectral-domain optical coherence tomograph (OCT). Prospective, cross-sectional study. One hundred fifty-five subjects (79 glaucoma and 76 normal subjects). One eye from each individual was selected randomly for optic disc and retinal nerve fiber layer (RNFL) imaging by the Heidelberg Retinal Tomograph (HRT; Heidelberg Engineering, GmbH, Dossenheim, Germany) and the Spectralis OCT (Heidelberg Engineering), respectively. Glaucoma was defined based on the presence of visual field defects with the Humphrey visual field analyzer (Carl Zeiss Meditec, Dublin, CA). The agreement of the categorical classification ("within normal limits," "borderline," and "outside normal limits") at the temporal, superotemporal, superonasal, nasal, inferonasal and inferotemporal sectors of the optic disc were evaluated (kappa statistics). The diagnostic sensitivity and specificity between optic disc and RNFL assessment were compared (McNemar's statistics). Area under the receiver operating characteristic curve (AUC) of OCT RNFL and HRT optic disc parameters were computed after adjustment of age, axial length, and optic disc area. Agreement of categorical classification, AUC of optic disc, and RNFL parameters. The agreement of categorical classification between HRT and Spectralis OCT were fair to moderate (kappa ranged between 0.30 and 0.53) except for global (kappa = 0.63) and inferotemporal (kappa = 0.68) measurements. Defining glaucoma as having "outside normal limits" in the global and/or in >or=1 of the sectoral measurements, the respective sensitivities of Spectralis OCT and HRT were 91.1% and 79.8% (P = 0.012) at a similar level of specificity (97.4% and 94.7%). The AUC of OCT global RNFL thickness (0.978) was greater than those of HRT global rim area (0.905), vertical cup-disc ratio (0.857), rim-disc area ratio (0.897), and multivariate discriminant analysis (0.880-0.925; all with P<or=0.028) after covariates adjustment. The diagnostic classification provided in the HRT and Spectralis OCT analysis report may not agree. At a comparable level of specificity, Spectralis OCT RNFL measurement attained a higher sensitivity than HRT optic disc measurement.
    Ophthalmology 12/2009; 117(2):267-74. · 5.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To develop a grading system to evaluate the scleral spur visibility and to investigate the association between this and the angle width. Sixty healthy normal subjects (33 with open angles and 27 with narrow angles on dark room gonioscopy) underwent anterior segment imaging with the Visante OCT (Carl Zeiss Meditec, Dublin, CA). The anterior chamber angles at 12-o' clock hour positions were imaged and analyzed. The scleral spur at each clock hour position was independently graded by 2 observers. A scleral spur visibility score (SSVS) of 2 denotes clear visibility of the scleral spur. SSVS of 0 and 1 represent undetectable and moderately by visibile scleral spur, respectively. The interobserver agreement of the SSVS was evaluated with kappa statistics. The associations between age, sex, axial length, refraction, angle width [mean anterior chamber angle detection with edge measurement and identification algorithm (ACADEMIA) angle], and the mean SSVS were examined with univariate and multivariate analyses. The mean gonioscopy grades were 3.6 and 0.8 for the open and narrow angle groups, respectively. The interobserver agreement in grading the scleral spur visibility was 0.71. The inferior angle (6:00) had the worst visibility of the scleral spur (SSVS=1.05+/-0.49) whereas the scleral spur of the nasal angle (3:00) showed the best visibility (SSVS=1.66+/-0.46). There were significant differences between SSVS at 6:00 and the other clock hours except for 5:00 and 7:00. The mean SSVS correlated positively with gonioscopy grade, anterior chamber depth, and ACADEMIA angle, and negatively with age. The only significant factor associated with scleral spur visibility was the ACADEMIA angle (P=0.013) after adjustment for other covariates. The visibility of the scleral spur is an important determinant of the dimension of anterior chamber angle.
    Journal of glaucoma 07/2009; 19(2):132-5. · 1.74 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate and compare the longitudinal variability of optical coherence tomography (OCT) and confocal scanning laser ophthalmoscopy (CSLO) optic disc measurements. A total of 25 normal and 50 glaucomatous eyes from 75 subjects were included in the analysis. The optic disc was measured by OCT and CSLO. Three separate measurements collected over an average period of 8.5+/-0.9 months were used to evaluate reproducibility. Univariate and multivariate regression analyses were performed to evaluate the associations between age, refraction, diagnosis (glaucoma or normal), visual field mean deviation, optic disc area, signal strength variance (OCT), optic disc area variance (OCT), image quality SD (CSLO), reference height variance (CSLO), and rim area variability. The intraclass correlation coefficient of optic disc measurements (except for optic disc area) ranged between 0.86 and 0.95 for OCT and between 0.89 and 0.96 for CSLO. The intraclass correlation coefficient for rim area measurement was significantly higher in CSLO (0.95) than that of OCT (0.86, P<0.001). After adjustment for other predictors, optic disc area variance and reference height variance were the most important factors responsible for rim area variability in OCT and CSLO, respectively. Although both OCT and CSLO have relatively low variability for optic disc measurements, CSLO demonstrates higher measurement reproducibility for rim area compared with OCT. Variations of disc area in OCT and reference height in CSLO constituted a significant proportion of the rim area variability during longitudinal assessment.
    Journal of glaucoma 02/2009; 18(2):101-6. · 1.74 Impact Factor
  • Carol Yim Lui Cheung, Christopher Kai-shun Leung
    Journal of Current Glaucoma Practice With Dvd. 01/2009;
  • [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate the reliability of lens density measurement with anterior segment optical coherence tomography (OCT) and its association with the Lens Opacity Classification System Version III (LOCS III) grading. Fifty-five eyes from 55 age-related cataract patients were included. One eye from each subject was selected at random for lens evaluation. After dilation, lens photographs were taken with a slit lamp and graded against the LOCS III standardised condition. Anterior segment OCT imaging was performed on the same eyes with a high-resolution scan. The association between the anterior segment OCT nucleus density measurement and LOCS III nuclear opalescence (NO) and nuclear colour (NC) scores was evaluated with the Spearman correlation coefficient. Anterior segment OCT measurement precision, coefficient of variation (CVw), and intraclass correlation coefficient (ICC) were calculated. The mean NO and NC scores were 3.39 (SD 1.10) and 3.37 (SD 1.27), respectively. Significant correlations were found between anterior segment OCT nuclear density measurements and the LOCS III NO and NC scores (r = 0.77 and 0.60, respectively, both with p<0.001). The precision, CVw and ICC of anterior segment OCT measurement were 2.05 units, 4.55% and 0.98, respectively. Anterior segment OCT nucleus density measurement is reliable and correlates with the LOCS III NO and NC scores.
    The British journal of ophthalmology 10/2008; 93(1):61-5. · 2.92 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To study the effect of optical coherence tomography (OCT) scan circle displacement on retinal nerve fibre layer (RNFL) measurement errors using cubic spline models. Forty-nine normal subjects were included in the analysis. In one randomly selected eye in each subject, RNFL thickness around the optic disc was measured by taking 16 circular scans of different sizes (scan radius ranged from 1 to 2.5 mm). The RNFL profile in each eye was constructed with a mathematical model using a smoothing spline approximation. Scan circle (diameter 3.4 mm) RNFL measurements (total average, superior, nasal, inferior, and temporal RNFL thicknesses) obtained from eight directions (superior, superonasal, nasal, inferonasal, inferior, inferotemporal, temporal, and superotemporal) displaced at different distances (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, and 0.7 mm) from the disc centre were then computed by a computer program and compared to the 'reference standard' where the scan circle is centred at the optic disc. RNFL measurement error was calculated as the absolute of (RNFL thickness(displaced) - RNFL thickness(reference standard)). The respective mean average, superior, nasal, inferior, and temporal RNFL measurement errors were 2.3+/-2.0, 4.9+/-4.5, 4.1+/-3.8, 6.2+/-7.6, and 3.8+/-3.5 microm upon 0.1 mm scan circle displacement, and 12.1+/-11.4, 27.8+/-18.4, 21.7+/-18.6, 34.8+/-22.9, and 15.2+/-10.7 microm upon 0.7 mm scan circle displacement. Significant differences of average and quadrant RNFL thicknesses were evident between centred and displaced scan circle measurements (all with P<0.001). RNFL measurement error increased in a monotonic fashion with increasing distance away from the disc and the change was direction-dependent. RNFL measurement error varies with the direction and distance of scan displacement. The superior and the inferior RNFL measurements are most vulnerable to scan displacement errors, whereas the average RNFL thickness is the least susceptible. Obtaining a well-centred scan is essential for reliable RNFL measurement in OCT.
    Eye (London, England) 09/2008; 23(6):1436-41. · 1.97 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate the repeatability and reproducibility of central corneal thickness (CCT) measurements obtained by 2 anterior segment optical coherence tomography (OCT) imaging systems and to examine their agreements with ultrasound pachymetry. Observational cross-sectional study. Fifty eyes from 50 healthy normal subjects were recruited. In one randomly selected eye in each subject, CCT was measured by slit-lamp OCT (SLOCT), Visante OCT, and ultrasound pachymetry. For anterior segment OCT measurements, both automatic and manual CCTs were obtained. Twenty-five of the 50 subjects were invited for 2 more visits within a week to evaluate repeatability and reproducibility of CCT measurement. Central corneal thickness measurement obtained by the 3 methods and their agreements. Intrasession and intersession within-subject standard deviation (S(w)), precision (1.96xS(w)), coefficient of variation (CV(w)) (100xS(w)/overall mean), and intraclass correlation coefficient (ICC) were calculated to evaluate repeatability and reproducibility. Good repeatability and reproducibility were found for both automatic and manual CCT measurements obtained by SLOCT and Visante OCT. For intrasession repeatability, CV(w) and ICC values ranged between 0.9% and 1.2% and 0.96 and 0.98, respectively. For intersession reproducibility, the respective CV(w) and ICC values ranged between 1.2% and 1.4% and 0.94 and 0.96. Although no significant difference was found between automatic/manual SLOCT measurements and ultrasound pachymetry, automatic Visante OCT CCT (535.7+/-30.2 microm) was significantly less than CCT with ultrasound pachymetry (550.3+/-31.14 microm) (P<0.001). In contrast, manual Visante OCT measurement (558.8+/-32.8 microm) was slightly higher than ultrasound pachymetry (P<0.001). Nevertheless, SLOCT and Visante OCT measurement of CCT had 95% limits of agreement comparable to that of ultrasound pachymetry. The best agreement was observed in the manual SLOCT measurement (95% limits of agreement between -15.5 and 11.7 microm). Both SLOCT and Visante OCT automatic and manual CCT measurements were reliable and showed comparable agreement with ultrasound pachymetry. Although the 2 anterior segment OCT imaging systems have similar design and working principles, clinicians should be aware of the differences in CCT measurement between the 2 anterior segment OCTs.
    Ophthalmology 06/2008; 115(5):796-801.e2. · 5.56 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To compare anterior chamber angle measurements obtained from two anterior segment optical coherence tomography (OCT) instruments and to evaluate their agreements and interobserver reproducibility. Forty-nine eyes from 49 healthy normal subjects were studied. The anterior chamber angle was imaged with the Visante anterior segment OCT (Carl Zeiss Meditec, Dublin, CA) and the slit lamp OCT (SLOCT, Heidelberg Engineering, GmbH, Dossenheim, Germany) on one randomly selected eye in each subject and measured by two independent observers. The angle-opening distance (AOD 500), the trabecular-iris angle (TIA 500), and the trabecular-iris space area (TISA 500) at the nasal and temporal angles were measured. The agreements between SLOCT and Visante OCT measurements and the interobserver reproducibility were evaluated. The mean nasal/temporal anterior chamber angles measured by Visante OCT and SLOCT were 527 +/- 249/572 +/- 275 microm (AOD), 0.180 +/- 0.091/0.193 +/- 0.102 mm(2) (TISA), and 38.1 +/- 12.3/39.6 +/- 13.2 degrees (TIA); and 534 +/- 234/628 +/- 254 microm (AOD), 0.191 +/- 0.089/0.217 +/- 0.093 mm(2)(TISA), and 37.8 +/- 10.1/40.6 +/- 10.7 degrees (TIA), respectively. No significant difference was found between Visante OCT and SLOCT measurements except the temporal TISA (P = 0.034). The interobserver coefficient of variation ranged between 4.4% and 7.8% for Visante OCT and 4.9% and 7.0% for SLOCT. The spans of 95% limits of agreement of the nasal/temporal angle measurements between Visante OCT and SLOCT were 437/531 mm(2), 0.174/0.186 mm(2), and 25.3/28.0 degrees for AOD, TISA, and TIA, respectively. Although Visante OCT and SLOCT demonstrate high interobserver reproducibility for anterior chamber angle measurements, their agreement was poor.
    Investigative ophthalmology & visual science 05/2008; 49(8):3469-74. · 3.43 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To examine the relationship between signal strength and retinal nerve fiber layer (RNFL) thickness measured by optical coherence tomography (OCT). Observational cross-sectional study. Forty normal subjects were recruited. Retinal nerve fiber layer (RNFL) thickness was measured by Stratus OCT (Carl Zeiss Meditec, Dublin, CA). In each eye, the focusing knob was adjusted to obtain 6 images with different signal strengths ranging from 5 to 10. The relationships between signal strength and RNFL thickness were examined using the Spearman correlation coefficient. The differences of RNFL thicknesses were compared with repeated-measures analysis of variance. Retinal nerve fiber layer thicknesses measured at different signal strengths. Significant differences were observed between measurements obtained at signal strength of 10 and those obtained with signal strength of less than 10 at the superior, nasal, and temporal clock hours. RNFL thickness generally increased with the signal strength, with significant correlations found with the total average, superior, and nasal clock hours RNFL thicknesses. Optical coherence tomography RNFL measurements vary significantly with signal strength. Obtaining the maximal possible signal strength is recommended for RNFL thickness measurement.
    Ophthalmology 03/2008; 115(8):1347-51, 1351.e1-2. · 5.56 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate the repeatability and reproducibility of anterior chamber angle measurement obtained by anterior segment optical coherence tomography. Twenty-five normal subjects were invited for anterior chamber angle imaging with an anterior segment optical coherence tomography (OCT) on one randomly selected eye in three separate visits within a week. Each eye was imaged three times under room light (light intensity = 368 lux) and three times in the dark during the first visit. In the subsequent visits, each eye was imaged once in the light and once in the dark. The angle opening distance (AOD 500) and the trabecular-iris angle (TIA 500) were measured by a single observer. Only the nasal angle was analysed. Intrasession and intersession within-subject standard deviation (Sw), precision (1.96xSw), coefficient of variation (CVw) (100xSw/overall mean), and intraclass correlation coefficient (ICC) were calculated to evaluate repeatability and reproducibility. For intrasession repeatability, the Sw, precision, CVw and ICC of AOD/TIA were 45 microm/2.4 degrees , 88 microm/4.7 degrees , 5.8%/4.8% and 0.97/0.95 in the light; and 45 microm/2.1 degrees , 88 microm/4.2 degrees , 7.0%/5.0% and 0.98/0.97 in the dark. For intersession reproducibility, the Sw, precision, CVw and ICC of AOD/TIA were 79 microm/3.5 degrees , 155 microm/6.8 degrees , 10.0%/7.0%, 0.91/0.89 in the light; and 64 microm/3.4 degrees , 124 microm/6.6 degrees , 9.9%/7.8% and 0.95/0.92 in the dark. The anterior segment OCT demonstrated reliable anterior chamber angle measurement in different lighting conditions with good repeatability and reproducibility.
    British Journal of Ophthalmology 12/2007; 91(11):1490-2. · 2.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To describe the use of anterior segment optical coherence tomography (OCT) in studying the dynamic dark-light changes of the anterior chamber angle. Thirty-seven normal subjects with open angles on dark-room gonioscopy and 18 subjects with narrow angles were analyzed. The dynamic dark-light changes of the anterior-chamber angle were captured with real-time video recording. The angle opening distance (AOD500) and trabecular iris space area (TISA500) of the nasal angle and the pupil diameter in each of the representative serial images were measured. Linear regression analysis was performed to investigate the association between AOD500/TISA500 and pupil diameter. Demographic and biometry measurements associated with the AOD difference (AOD500((light)) - AOD500((dark))) and TISA difference (TISA500((light)) - TISA500((dark))) were analyzed with univariate and multivariate regression models. The AOD500/TISA500 measured in the light in the open-angle and the narrow-angle groups were 694 +/- 330 microm/0.24 +/- 0.10 mm(2) and 265 +/- 78 microm/0.10 +/- 0.03 mm(2), respectively. These values were significantly greater than the AOD500/TISA500 measured in the dark (492 +/- 265 microm/0.16 +/- 0.08 mm(2) and 119 +/- 82 microm/0.05 +/- 0.04 mm(2), respectively, all with P < 0.001). The ranges of the AOD/TISA difference were 13 to 817 microm/0.011 to 0.154 mm(2), with an average of 180 microm/0.073 mm(2). Multivariate regression analysis identified a positive correlation between anterior chamber depth and the AOD/TISA difference. Fifty eyes showed significant correlations between AOD/TISA and pupil diameter, whereas one eye showed no association. Four eyes in the narrow angle group developed appositional angle closure in the dark. The dynamic dark-light changes of the anterior chamber angle can be imaged and analyzed with anterior segment OCT. Although the angle width generally decreased linearly with increasing pupil diameter, the differences of the angle width measured in the dark and in the light varied substantially among individuals.
    Investigative Ophthalmology &amp Visual Science 09/2007; 48(9):4116-22. · 3.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate the relationships between optic disc measurements, obtained by an optical coherence tomograph and a confocal scanning laser ophthalmoscope, and myopia. One hundred thirty-three eyes from 133 healthy subjects with mean spherical equivalent -6.0 +/- 4.2 D (range, -13.13 to +3.25 D) were analyzed. Optic disc measurements including disc area, rim area, cup area, cup-to-disc area, and vertical and horizontal ratios were obtained with an optical coherence tomograph (StratusOCT; Carl Zeiss Meditec Inc., Dublin, CA) and a confocal scanning laser ophthalmoscope (Heidelberg Retina Tomograph, HRT 3; Heidelberg Engineering, GmbH, Dossenheim, Germany). The modified axial length method derived from prior published work was used to correct the OCT measurements for ocular magnification. Bland-Altman plots were used to evaluate the agreement for each optic disc parameter. Associations between optic disc area and axial length/spherical equivalent were evaluated by linear regression analysis. Disc area increased with the axial length/negative spherical equivalent in the HRT and the corrected OCT measurements although opposite directions of associations were found when the OCT measurements were not corrected for magnification. The difference of the corrected OCT and HRT disc area (corrected OCT disc area minus HRT disc area) was correlated with the axial length (r = 0.195, P = 0.025). When the ametropia was limited to -8.0 to +4.0 D, the correlations became insignificant in the HRT. Using the corrected OCT measurements, disc area, rim area, and cup area, cup-to-disc area, and cup-to-disc horizontal and vertical ratios were significantly larger than those measured by the HRT, with a span of 95% limits of agreement at 1.99, 1.33, and 1.86 mm(2) for the areas, 0.34, 0.53, and 0.58 for the ratios, respectively. While optic disc area generally increased with the axial length and myopic refraction, the HRT measurements demonstrated that optic disc size was largely independent of axial length and refractive error between -8 and +4 D. OCT may overestimate optic disc size in myopic eyes and results in poor agreement between the two instruments.
    Investigative Ophthalmology &amp Visual Science 08/2007; 48(7):3178-83. · 3.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To compare the relationships between optic nerve structural measures and visual function, as well as the diagnostic sensitivity for glaucoma detection between the retinal nerve fiber layer (RNFL) and neuroretinal rim measurements. A total of 101 normal and 156 glaucomatous eyes of 257 enrolled subjects were examined. RNFL thickness was measured by optical coherence tomography, and the neuroretinal rim (rim area, rim/disc area, and rim volume) was measured with a confocal scanning laser ophthalmoscope. The relationship between the structural measures and visual field sensitivity was evaluated with linear and non-linear-regression (quadratic and logarithmic) models. The coefficient of determination (R2) was calculated, and the regression models were compared with Alkaike's information criteria and the F test. The diagnostic sensitivity for glaucoma detection in each structural measure was determined by the area under the receiver operating characteristic curve (AUC). The relationship of the RNFL, rim area, rim/disc area, and rim volume with visual function was best described with nonlinear regression models (quadratic regression for the RNFL [R2 = 0.383]), rim area [R2 = 0.303]), and rim/disc area [R2 = 0.265]; and logarithmic regression for rim volume [R2 = 0.175]). The change of visual sensitivity at each level of structural damage was highest for the RNFL. The AUC for the RNFL also was higher than the neuroretinal rim measures. In this study population, at 90% specificity, the diagnostic sensitivities for detecting glaucomatous damage was 82.7%, 67.3%, 67.3%, and 52.6% for the RNFL, rim area, rim/disc area, and rim volume, respectively. (These values would apply only to a group with inclusion criteria and disease severity similar to those of the present cohort.) The RNFL showed a stronger structure-function association and a higher diagnostic sensitivity for glaucoma detection than did the neuroretinal rim.
    Investigative Ophthalmology &amp Visual Science 07/2007; 48(6):2644-52. · 3.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To investigate the relationship between myopia and macular thickness, as measured by optical coherence tomography. A total of 143 normal subjects comprising 80 eyes with high myopia (spherical equivalent [SE] < -6.0 D), 37 eyes with low to moderate myopia (SE between -6.0 and -0.5 D), and 26 nonmyopic eyes (SE > -0.5 D) were analyzed in this cross-sectional study. Total average, foveal, and inner and outer average macular thicknesses measured by the StratusOCT (Carl Zeiss Meditec Inc., Dublin, CA) were compared among the three diagnostic groups. Associations between macular thickness and refractive error/axial length were evaluated by linear regression analysis. The minimum foveal and average foveal (1-mm ring on the OCT retinal thickness map) thicknesses were significantly greater, and the outer ring macular (3-6-mm) thicknesses significantly lower in the high myopic eyes than in the low to moderate myopic and nonmyopic eyes. No significant difference was found in the inner ring (1-3-mm) macular thickness measurements among the groups. There was a positive correlation between the axial length and the average foveal thickness (r = 0.374, P < 0.001). Negative correlations were found between axial length and the average outer ring macular thickness (r= -0.471, P < 0.001) and total average macular thickness (r= -0.311, P < 0.001). Retinal thickness is related to refractive error/axial length in normal subjects with regional variations in correlation within the 6-mm macular region. Analysis of macular thickness in the evaluation of macular diseases and glaucoma should be interpreted only in the context of refractive errors and the location of measurement.
    Investigative Ophthalmology &amp Visual Science 02/2007; 48(1):376-82. · 3.44 Impact Factor