Lisandro M. Sakata

Optical coherence tomography of the retina and optic nerve – a review

Optical coherence tomography (OCT) is a rapid non‐contact method that allows in vivo imaging of the retina, optic nerve head and retinal nerve fibre layer (RNFL). Since its introduction in Ophthalmology approximately a decade ago, the use of this technology has disseminated into the clinical practice. OCT has proven to be a useful ancillary tool for assessing retinal diseases because of its capability to provide cross‐sectional images of the retina, and also to perform quantitative analysis of retinal morphology. In glaucoma, the OCT represents one of the methods capable of documenting and analysing optic disc and RNFL morphology in attempt to diagnose and monitor glaucomatous optic neuropathy. Recently, the spectral domain OCT became available, a new technique that allowed major improvements particularly regarding image acquisition speed and image resolution. Future studies will address how these major technological advances will impact the use of the OCT in research and clinical practice.

Assessment of the Scleral Spur in Anterior Segment Optical Coherence Tomography Images

OBJECTIVE To assess visibility of the scleral spur in anterior segment optical coherence tomography (AS-OCT) images. METHODS This cross-sectional observational study included 502 participants aged 50 years or older who had no previous ophthalmic problems and were recruited from a community clinic in Singapore. All participants underwent gonioscopy and AS-OCT (Visante; Carl Zeiss Meditec, Dublin, California). Scleral spur location was assessed in AS-OCT images by 2 examiners with glaucoma subspecialty training and was defined as the point where there was an inward protrusion of the sclera with a change in curvature of its inner surface. RESULTS Scleral spur location could be determined in 72% of the images of the right eye. Its location on AS-OCT images was less detectable in quadrants with a closed angle on gonioscopy and also in images obtained in the superior and inferior compared with the nasal and temporal quadrants (64%, 67%, 75%, and 80%, respectively; P < .001). CONCLUSIONS The inability to detect the scleral spur may hamper quantitative analysis of anterior chamber angle parameters that are dependent on the location of this anatomical structure, particularly in the superior and inferior quadrants. New parameters independent of the scleral spur may be useful for detecting eyes at risk of angle closure.

Quantitative Iris Parameters and Association with Narrow Angles

PURPOSE To investigate the relationship between quantitative iris parameters (iris curvature [I-Curv], iris area [I-Area], and iris thickness) and the presence of narrow angles. DESIGN Cross-sectional, community-based study. PARTICIPANTS We recruited 2047 subjects >50 years old without ophthalmic symptoms from a community clinic in Singapore. METHODS All subjects underwent gonioscopy and anterior segment optical coherence tomography (AS-OCT) under dark conditions. An eye was considered to have narrow angles if the posterior pigmented trabecular meshwork was not visible for >/=180 degrees on nonindentation gonioscopy with the eye in the primary position. Customized software was used on horizontal AS-OCT scans to measure I-Curv, I-Area, and iris thickness 750 mum (IT750) and 2000 mum (IT2000) from the scleral spur. The average of both temporal and nasal measured values of the right eye was used for analysis. MAIN OUTCOME MEASURES The association between iris parameters and narrow angles on gonioscopy. RESULTS Iris parameters from 1465 eyes (71.6%) were available for analysis. Of these, 315 subjects (21.5%) had narrow angles. The mean I-Curv (0.366 vs 0.259 mm; P<0.020), IT750 (0.476 vs 0.453 mm; P<0.001), and IT2000 (0.491 vs 0.482 mm; P = 0.010) were greater in persons with than without narrow angles. After adjusting for age, gender, anterior chamber depth, axial length, and pupil size, the greater I-Curv, I-Area, IT750, and IT2000 were significantly associated with narrow angles (odds ratio [OR] 2.5 and 95% confidence interval [CI], 1.3-5.1; OR, 2.7 and 95% CI, 1.6-4.8; OR, 2.6 and 95% CI, 1.6-4.1; OR, 2.7 and 95% CI, 1.5-4.7, comparing 4th with 1st quartile for each parameter, respectively). In stratified analysis, women and subjects aged >/=60 years had stronger associations for most iris parameters with narrow angles than men and younger subjects. CONCLUSIONS Quantitative iris parameters (I-Curv, I-Area, and iris thickness) are independently associated with narrow angles, particularly in women and older subjects. These data provide further insights into the pathogenesis of angle closure in Singaporeans. FINANCIAL DISCLOSURE(S) Proprietary or commercial disclosure may be found after the references.

Quantitative analysis of anterior segment optical coherence tomography images : the Zhongshan Angle Assessment Program

Aim: To describe a new image analysis method and software for anterior chamber images obtained by the anterior-segment optical coherence tomography (AS-OCT) and to assess its intraobserver and interobserver measurement reproducibility. Methods: Twenty 8-bit greyscale 600×300 AS-OCT images with apparent wide angles and 20 images with apparent narrow angles were consecutively selected from a database. Two glaucoma fellowship-trained ophthalmologists used proprietary image analysis software to analyse the images twice. Algorithms defined the borders and curvatures of anterior chamber (AC) structures and measured AC parameters using scleral spur location as the only observer input. The intraobserver and interobserver reproducibility of scleral spur location and angle parameters was calculated in terms of limits of agreement (LOA; mean of differences±1.96SD of differences) and coefficient of variation (CV; SD of differences/overall mean). Results: The analysis software successfully measured all parameters in all images. When the same image was assessed twice by the same grader, the mean differences ranged from 0 to 0.010 mm in linear measurements and 0.001 to 0.006 mm2 in angle area measurements. LOA tended to be greater in the wider angles. The upper and lower limit values of LOAs were approximately 1/5 to 1/4 of the overall mean. Measurements between two graders had a higher variance. Reproducibility in terms of CV was better in wide angles when compared with narrow angles. The reproducibility of scleral spur placement between observers was poorer in narrow angles (p = 0.001). About 50% of the interobserver variance in angle-area measurements was attributable to the variance of scleral spur placement, while this proportion was only 10–20% in linear measurements. Conclusions: Determination of angle parameters using semiautomated software leads to variability in measurement. Variability increases when more than one observer identifies the scleral spur. Variability differs in narrow and open angles, and so including both types is essential when evaluating angle-assessment software. A fully automated analysis and higher image resolution would likely improve quantification of Visante AS-OCT images.

Novel Association of Smaller Anterior Chamber Width with Angle Closure in Singaporeans

PURPOSE To describe variations in anterior chamber width (ACW) and investigate its association with the presence of narrow angles. DESIGN Cross-sectional study. PARTICIPANTS We recruited 2047 subjects aged 50 years or more from a community polyclinic and 111 subjects with primary angle closure (PAC) or primary angle closure glaucoma (PACG) from an eye hospital in Singapore. METHODS All participants underwent gonioscopy, anterior chamber depth (ACD) and axial length (AL) measurement (IOLMaster; Carl Zeiss, Jena, Germany), and anterior-segment optical coherence tomography (AS-OCT, Visante, Carl Zeiss Meditec, Dublin, CA). Customized software was used to measure the ACW, defined as the distance between the scleral spurs in the horizontal (nasal-temporal) axis of AS-OCT scans. An eye was deemed to have narrow angles if the posterior trabecular meshwork was not visible for at least 180 degrees on non-indentation gonioscopy with the eye in the primary position. MAIN OUTCOME MEASURES Anterior chamber width and narrow angles. RESULTS Data on 1465 community-based subjects were available for analysis. Anterior chamber width was significantly smaller in women compared with men (11.70 mm vs. 11.81 mm, respectively, P<0.001) and decreased significantly with age (P for trend <0.001). Significant predictors of smaller ACW were lower educational level, lower body mass index, shorter AL, shallower ACD, and Chinese race. Of the 1465 subjects, 315 (21.5%) had narrow angles on gonioscopy. Mean ACW was smaller in eyes with narrow angles compared with those without narrow angles (11.60 mm vs. 11.80 mm, P<0.001). The age- and gender-adjusted odds ratio for the highest quartile compared with the lower 3 quartiles of ACW with the presence of narrow angles was 3.4 (95% confidence interval, 2.3-5.0; P for trend <0.001). Hospital-based subjects with PAC/PACG had even smaller ACW than community subjects with narrow angles (11.33 mm vs. 11.60 mm, P<0.001). CONCLUSIONS In this cross-sectional study, ACW was smaller in women, Chinese persons, and older persons, and was associated with narrow angles in 2 different study populations. These data suggest that a smaller ACW may represent a novel risk indicator for angle closure.

The relation between intraocular pressure peak in the water drinking test and visual field progression in glaucoma

Aim: To compare the results of the water drinking test between glaucomatous eyes with and without visual field progression. Methods: Retrospective analysis of 76 eyes of 76 open angle glaucoma patients followed for a mean period of 26.0 (SD 13.8) months. Patients were submitted to the water drinking test at the beginning of the follow up period. Reliable achromatic automated perimetry tests performed during the studied period were used to characterise visual field progression. All subjects were under clinical therapy and had an intraocular pressure (IOP) lower than 17 mm Hg monitored by isolated measurements during the follow up period. The results of the water drinking test were compared between glaucomatous eyes with and without visual field progression. Results: Twenty eight eyes reached definite visual field progression. There were no significant differences in the mean age, sex, race, basal IOP, number of antiglaucomatous drugs, initial mean deviation (MD), and corrected pattern standard deviation (CPSD) between eyes that showed visual field progression and the ones who did not progress. A significant difference of 1.9 (SD 0.6) mm Hg (p = 0.001, analysis of covariance; 95% CI 0.8 to 3.0) was observed between glaucomatous eyes that showed visual field deterioration and glaucomatous eyes that did not progress. A significant difference of 16.8% (SD 4.6%) in the mean percentage of IOP variation was also observed between the two groups (p<0.001, analysis of covariance; 95% CI 7.7 to 26.0). Conclusions: Mean IOP peak and percentage of IOP variation during water drinking test were significantly higher in patients with visual field progression compared with patients who did not progress.

Diagnostic Performance of Anterior Chamber Angle Measurements for Detecting Eyes With Narrow Angles: An Anterior Segment OCT Study

OBJECTIVE To assess the diagnostic performance of angle measurements from anterior segment optical coherence tomography (AS-OCT) images for identifying eyes with narrow angles. METHODS We conducted a community-based cross-sectional study of individuals 50 years or older who had phakic eyes and who underwent AS-OCT imaging in the dark by a single operator and gonioscopy by an ophthalmologist masked to AS-OCT findings. An eye was considered to have narrow angles if the posterior pigmented trabecular meshwork was not visible for at least 180° on gonioscopy. Horizontal AS-OCT images were analyzed for the following measurements using customized software: angle opening distance (AOD) at 250, 500, and 750 μm from the scleral spur; trabecular-iris space area (TISA) at 500 and 750 μm; and angle recess area (ARA) at 750 μm. Areas under the receiver operating characteristic curves (AUCs) were generated for AOD, TISA, and ARA to assess the performance of these measurements in detecting eyes with narrow angles. RESULTS Of 2047 individuals examined, 582 were excluded mostly because of poor image quality or inability to locate the scleral spur. Of the remaining 1465 participants, 315 (21.5%) had narrow angles on gonioscopy. Mean (SD) age was 62.7 (7.7) years, 54.1% were women, and 90.0% were Chinese. The AUCs were highest for AOD750 in the nasal (0.90 [95% confidence interval, 0.89-0.92]) and temporal (0.91 [0.90-0.93]) quadrants. CONCLUSIONS The AOD750 is the most useful angle measurement for identifying individuals with gonioscopic narrow angles in gradable AS-OCT images. Poor definition of the scleral spur precludes quantitative analysis in approximately 25% of AS-OCT images.

Determinants of lens vault and association with narrow angles in patients from Singapore.

PURPOSE To describe the distribution and determinants of lens vault and to investigate the association of lens vault with narrow angles. DESIGN Prospective cross-sectional study. METHODS Phakic subjects 50 years and older were evaluated at a primary healthcare clinic with gonioscopy, partial laser interferometry, and anterior segment optical coherence tomography (AS-OCT). Narrow angles were defined as posterior trabecular meshwork not visible for ≥2 quadrants on non-indentation gonioscopy. Lens vault was defined as the perpendicular distance between the anterior pole of the crystalline lens and the horizontal line joining the 2 scleral spurs on horizontal AS-OCT scans. Analysis of covariance, multivariate logistic regression, and area under the receiver operating characteristic curves (AUC) were performed. RESULTS Of the 2047 subjects recruited, 582 were excluded because of poor image quality or inability to locate scleral spurs, leaving 1465 subjects for analysis. Eyes with narrow angles had greater lens vault compared to eyes with open angles (775.6 µm vs 386.5 µm, P < .0001). Women had significantly greater lens vault than men (497.28 µm vs 438.56 µm, P < .001), and lens vault increased significantly with age (P for trend <.001). Adjusted for age and sex, significant associations with greater lens vault were shorter axial length, shallower anterior chamber depth(ACD), higher intraocular pressure, and more hyperopic spherical equivalent (all P < .001). On multivariate analysis, subjects with lens vault >667.6 µm were more likely to have narrow angles (OR 2.201, 95% CI: 1.070-4.526) compared to those with lens vault ≤462.7 µm. The AUC for lens vault (0.816) and ACD (0.822) for detecting narrow angles were similar (P = .582). CONCLUSIONS Lens vault was independently associated with narrow angles and may be useful in screening to detect eyes with narrow angles.

Comparison of Visante and slit-lamp anterior segment optical coherence tomography in imaging the anterior chamber angle

AimsTo compare the diagnostic performance of two anterior segment optical coherence tomography (AS-OCT) devices in assessing the anterior chamber angle (ACA).MethodsVisante-OCT and slit-lamp-OCT (SL-OCT) were performed on 101 patients by a single operator. The AS-OCT images were processed by customised ‘dewarping’ software and assessed by two glaucoma specialists masked to clinical findings. A closed ACA was defined by the presence of contact between the iris and angle anterior to the scleral spur. Measurements of the ACA, anterior chamber depth (ACD), and pupil diameter were analysed. Gonioscopy was performed by another examiner masked to AS-OCT findings.ResultsQualitative analysis could be carried out in 83 (83%) eyes and quantitative analysis in 61 (60%) eyes. A closed angle in at least one quadrant of the eye was observed in 30 eyes with gonioscopy; Visante-OCT imaging identified 29 of 30 (97%) and SL-OCT imaging identified 27 of 30 (90%) of these eyes (P=0.50, McNemar test). Visante-OCT detected more eyes with at least one closed quadrant than SL-OCT (55 vs46 eyes, respectively, P=0.01). Overall, SL-OCT had better agreement with gonioscopy than with Visante-OCT. Both AS-OCTs showed good agreement for ACD measurements; however, SL-OCT tended to provide consistently higher ACA measurements and smaller pupil diameters than did Visante-OCT.ConclusionsBoth AS-OCT devices detected most of the eyes with closed ACA on gonioscopy. However, Visante-OCT detected more closed ACAs than did SL-OCT. The better agreement between SL-OCT and gonioscopy is likely because of the use of visible light during both examinations. The ACA measurements obtained with each device are not interchangeable.

Evaluation of scanning protocols for imaging the anterior chamber angle with anterior segment-optical coherence tomography.

PurposeTo evaluate different anterior segment-optical coherence tomography (AS-OCT) scanning protocols for detecting eyes with angle closure. MethodsThis cross-sectional study enrolled 2104 subjects from a community clinic in Singapore. All participants underwent AS-OCT imaging in the dark (Visante, Carl-Zeiss, Meditec, Dublin, CA), and gonioscopy with a Goldmann 2-mirror and a Sussman lens by an experienced examiner. The anterior chamber angle in a particular quadrant was considered closed on gonioscopy if the posterior trabecular meshwork could not be seen; and on AS-OCT by the presence of contact between the iris and angle wall anterior to the scleral spur. Protocols using combinations of AS-OCT scans of different quadrants of the eye were compared. ResultsA total of 1853/2104 right eyes could be graded in all 4 quadrants. In all, 380 (20.5%) eyes had closed angles in at least 2 quadrants on gonioscopy. The AS-OCT scanning protocol that only imaged the inferior quadrant showed the best area under the receiving operating characteristic curve (AUC 0.76, sensitivity 84%, specificity 69%) for detecting angle closure. Although technically easier to obtain, the protocol that only included the nasal-temporal quadrants had the lowest AUC (AUC 0.67, sensitivity 47%, specificity 88%), whereas scanning the superior-inferior quadrants showed high sensitivity for detecting angle closure (92%), but low specificity (54%). ConclusionsUsing the results obtained in a research setting, the diagnostic performance of AS-OCT varied according to the adopted scanning protocol. The inferior quadrant-only protocol showed the best diagnostic performance but the low specificity would limit its use for population screening.