Christopher Kai-Shun Leung

Comparison of macular thickness measurements between time domain and spectral domain optical coherence tomography.

PURPOSE To compare macular thickness measurements obtained from time domain optical coherence tomography (OCT) and spectral domain OCT and to evaluate their repeatability and agreement. METHODS Thirty-five healthy normal subjects were included. In one randomly selected eye in each subject, three serial macular measurements were obtained from a time domain OCT (Stratus OCT, Carl Zeiss Meditec, Dublin, CA) and a spectral domain OCT (3D OCT; Topcon, Tokyo, Japan) by an experienced technician in random order. Total and regional macular thicknesses obtained by the two OCTs were compared. Their agreement was examined with Bland-Altman plots. Repeatability (2.77 x within subject SD [Sw]), coefficient of variation (CVw; Sw/overall mean), and intraclass correlation coefficient (ICC) were calculated to evaluate repeatability. RESULTS Low variability for macular thickness measurements was found in both time domain and spectral domain OCTs. The range of the respective CVw and ICC values were 1.6% to 3.2% and 0.85 to 0.91 for Stratus OCT and 0.6% to 2.4% and 0.92 to 0.99 for 3D OCT. 3D OCT demonstrated better repeatability for total and regional macular thicknesses (all with P <or= 0.014). The foveal and total macular thicknesses measured by 3D OCT were significantly greater than those measured by Stratus OCT (both with P < 0.001). The spans of 95% limits of agreement for foveal and total macular thicknesses were 33.9 and 21.3 mum, respectively. CONCLUSIONS Although both time domain and spectral domain OCTs are reliable for macular thickness measurements, spectral domain OCT has better measurement repeatability compared with time domain OCT. Macular measurements obtained from the two OCT systems may not be used interchangeably.

Relationship between Retinal Nerve Fiber Layer Measurement and Signal Strength in Optical Coherence Tomography

PURPOSE To examine the relationship between signal strength and retinal nerve fiber layer (RNFL) thickness measured by optical coherence tomography (OCT). DESIGN Observational cross-sectional study. PARTICIPANTS Forty normal subjects were recruited. METHODS 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. MAIN OUTCOME MEASURES Retinal nerve fiber layer thicknesses measured at different signal strengths. RESULTS 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. CONCLUSIONS Optical coherence tomography RNFL measurements vary significantly with signal strength. Obtaining the maximal possible signal strength is recommended for RNFL thickness measurement.

Retinal Nerve Fiber Layer Imaging with Spectral-Domain Optical Coherence Tomography Analysis of the Retinal Nerve Fiber Layer Map for Glaucoma Detection

OBJECTIVE To evaluate the diagnostic performance of the retinal nerve fiber layer (RNFL) thickness deviation map imaged by a spectral-domain optical coherence tomography (OCT; Cirrus HD-OCT, Carl Zeiss Meditec Inc, Dublin, CA) and compare its sensitivity and specificity for glaucoma detection with circumpapillary RNFL measurement derived from the standard 3.46 mm diameter circle scan. DESIGN Prospective, cross-sectional study. PARTICIPANTS We included 102 normal subjects and 121 glaucoma patients. METHODS One eye from each individual was imaged with Cirrus HD-OCT and Stratus OCT (Carl Zeiss Meditec Inc.). Glaucoma was defined based on the presence of visual field defects with the Humphrey visual field analyzer (Carl Zeiss Meditec Inc.). A scoring system (0-5) was developed to analyze the RNFL thickness deviation map taking the defect size, shape, depth, location, and distance from the disc margin into consideration. Each of these features was scored independently by a masked observer with a highest total score of 5 (glaucomatous RNFL defect) and a lowest score of 0 (no RNFL defect). Sensitivity and specificity were computed with a score of > or =3, > or =4, or =5. The diagnostic performance of circumpapillary RNFL measurement was analyzed with clock-hour and average RNFL thickness categorical classification. MAIN OUTCOME MEASURES Diagnostic sensitivity and specificity. RESULTS The sensitivities of the RNFL thickness deviation map ranged between 95.0% and 97.5%. There were significant differences in specificity between a map score of 5, a map score of > or =4 (87.3%), and a map score > or =3 (72.5%; P< or =0.014). A map score of 5 attained a significantly higher sensitivity (95.0%) compared with clock-hour or average RNFL thickness categorical classification by Stratus OCT or Cirrus HD-OCT (46.3%-88.4%; P< or =0.033) at a comparable level of specificity (95.1%), except when glaucoma was detected as having > or =1 clock-hour at the < or =5% level by Cirrus HD-OCT in which an equally high sensitivity (93.4%) was found but at the expense of a significantly lower specificity (83.3%; P<0.001). CONCLUSIONS Analysis of the RNFL thickness deviation map provides additional spatial and morphologic information of RNFL damage and significantly improves the diagnostic sensitivity for glaucoma detection compared with conventional circumpapillary RNFL measurement.

Retinal Nerve Fiber Layer Imaging with Spectral-domain Optical Coherence Tomography: Patterns of Retinal Nerve Fiber Layer Progression

OBJECTIVE To examine the use of the retinal nerve fiber layer (RNFL) thickness map generated by a spectral-domain optical coherence tomography (OCT) to detect RNFL progression and identify the pattern of progressive changes of RNFL defects in glaucoma. DESIGN Prospective, longitudinal study. PARTICIPANTS One hundred eighty-six eyes of 103 glaucoma patients. METHODS Patients were followed at 4-month intervals for ≥ 36 months for RNFL imaging and visual field examination. Both eyes were imaged by the Cirrus HD-OCT (Carl Zeiss Meditec Inc., Dublin, CA) and had visual field testing at the same visits. We defined RNFL progression by Guided Progression Analysis (Carl Zeiss Meditec) of serial RNFL thickness maps. The pattern of RNFL progression was evaluated by comparing the baseline RNFL thickness deviation map and the RNFL thickness change map. Visual field progression was defined by trend analysis of visual field index and event analysis based on the Early Manifest Glaucoma Trial criteria. MAIN OUTCOME MEASURES The presence and the pattern of RNFL progression. RESULTS A total of 2135 OCT images were reviewed. Twenty-eight eyes (15.1%) from 24 patients (23.3%) had RNFL progression detected by RNFL thickness map analysis. Three RNFL progression patterns were observed: (1) widening of RNFL defects (24 eyes, 85.7%), (2) deepening of RNFL defects (2 eyes, 7.1%, both had concomitant widening of RNFL defects), and (3) development of new RNFL defects (5 eyes, 17.9%). The inferotemporal meridian (324°-336°) 2.0 mm away from the optic disc center was the most frequent location where RNFL progression was detected. Thirteen eyes (46.4%) had concomitant visual field progression; 61.5% (n = 8) of these had RNFL progression that preceded or occurred concurrently with visual field progression. Forty-two eyes from 37 patients (22.6%) had visual field progression by trend and/or event analyses without progression in the RNFL thickness map. CONCLUSIONS Analysis of serial RNFL thickness maps generated by the spectral-domain OCT facilitates the detection of RNFL progression in glaucoma.

Central corneal thickness measurements using Orbscan II, Visante, ultrasound, and Pentacam pachymetry after laser in situ keratomileusis for myopia

PURPOSE: To compare corneal pachymetry assessment using 4 measurement methods in eyes after laser in situ keratomileusis (LASIK) for myopia. SETTING: Department of Ophthalmology & Visual Sciences, The Chinese University of Hong Kong, Hong Kong Eye Hospital, Hong Kong SAR. METHODS: Fifty‐two consecutive patients (103 eyes) who had LASIK for the correction of myopia had Orbscan II (Bausch & Lomb), Visante (Carl Zeiss Meditec), Pentacam (Oculus, Inc.), and ultrasound (US) pachymetry (Sonomed, 200P) 6 months after surgery. Data were analyzed using the paired sample t test, Bland‐Altman plots, and linear regression. RESULTS: The mean postoperative pachymetry measured by US, Orbscan (0.89 acoustic factor), Pentacam, and Visante pachymetry were 438.2 μm ± 41.18 (SD), 435.17 ± 49.63 μm, 430.66 ± 40.23 μm, and 426.56 ± 41.6 μm, respectively. Compared with the US measurement, Pentacam and Visante measurements significantly underestimated corneal thickness by a mean of 7.54 ± 15.06 μm (P<.01) and 11.64 ± 12.87 μm (P<.01), respectively. There was no statistically significant difference between US and Orbscan measurements. CONCLUSION: Pentacam and Visante measurements of corneal thickness 6 months after LASIK were significantly less than those obtained using Orbscan and US pachymetry, although all 4 measurement methods showed a high correlation with each other.

Repeatability and Reproducibility of Anterior Chamber Angle Measurement with Anterior Segment Optical Coherence Tomography

Aim: To evaluate the repeatability and reproducibility of anterior chamber angle measurement obtained by anterior segment optical coherence tomography. Methods: 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 (1.96×Sw), coefficient of variation (CVw) (100×Sw/overall mean), and intraclass correlation coefficient (ICC) were calculated to evaluate repeatability and reproducibility. Results: For intrasession repeatability, the Sw, precision, CVw and ICC of AOD/TIA were 45 &mgr;m/2.4°, 88 &mgr;m/4.7°, 5.8%/4.8% and 0.97/0.95 in the light; and 45 &mgr;m/2.1°, 88 &mgr;m/4.2°, 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 &mgr;m/3.5°, 155 &mgr;m/6.8°, 10.0%/7.0%, 0.91/0.89 in the light; and 64 &mgr;m/3.4°, 124 &mgr;m/6.6°, 9.9%/7.8% and 0.95/0.92 in the dark. Conclusions: The anterior segment OCT demonstrated reliable anterior chamber angle measurement in different lighting conditions with good repeatability and reproducibility.

Retinal Nerve Fiber Layer Imaging with Spectral-Domain Optical Coherence Tomography: Pattern of RNFL Defects in Glaucoma

OBJECTIVE To characterize the distribution pattern, angular width, and area of retinal nerve fiber layer (RNFL) defects in glaucoma using spectral-domain optical coherence tomography (OCT). DESIGN Prospective, cross-sectional study. PARTICIPANTS We included 113 normal subjects and 116 glaucoma patients. METHODS One eye from each individual was randomly selected for Cirrus HD-OCT (Carl Zeiss Meditec Inc., Dublin, CA) RNFL imaging of the 6 × 6-mm² parapapillary region. The RNFL defects were identified in the RNFL thickness deviation map as superpixels coded in red. The angular location and the angular width of RNFL defects were measured. The proportion of area with RNFL measurements within the normal ranges in the RNFL thickness deviation map was expressed as the RNFL area index (RAI): 1 - [area of superpixels coded in red/(6 × 6 - optic disc and parapapillary atrophic area)]. The diagnostic performance between RAI and average RNFL thickness was compared with the area under the receiver operating characteristic curve after adjusting refraction, signal strength, optic disc, and parapapillary atrophic areas. MAIN OUTCOME MEASURES Frequency distribution profiles and distribution patterns of RNFL defects, diagnostic sensitivity and specificity of RAI, and average RNFL thickness. RESULTS The RNFL defects in glaucoma were most frequently found at the inferotemporal meridian at 284° (80.4%), followed by the superotemporal meridians at 73° (54.2%). The respective proportions of localized (angular width ≤ 30°) and diffuse (angular width > 30°) RNFL defects were 11.4% and 70.5% in mild glaucoma (MD ≥ 6 dB), and 4.2% and 94.5% in moderate to advanced glaucoma (MD < -6 dB). The RAI was 90.2 ± 6.4% and 83.6 ± 7.4% in the mild and moderate to advanced glaucoma groups, respectively. At a specificity of 90.0%, the respective diagnostic sensitivity of RAI and average RNFL thickness was 95.7% (95% confidence interval, 92.2-99.1%) and 94.0% (90.1-99.1%). CONCLUSIONS Analysis of the pattern of RNFL defects with spectral domain OCT imaging offers important insights in understanding the characteristics of RNFL damage. As RNFL defects expand in size as the disease progresses, measurement of the angular width and area of RNFL defects can provide an additional dimension for evaluation of glaucoma.

Anterior chamber angle measurement with anterior segment optical coherence tomography: a comparison between slit lamp OCT and Visante OCT.

PURPOSE To compare anterior chamber angle measurements obtained from two anterior segment optical coherence tomography (OCT) instruments and to evaluate their agreements and interobserver reproducibility. METHODS 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. RESULTS 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. CONCLUSIONS Although Visante OCT and SLOCT demonstrate high interobserver reproducibility for anterior chamber angle measurements, their agreement was poor.

Analysis of bleb morphology after trabeculectomy with Visante anterior segment optical coherence tomography

Background: To describe the use of anterior segment optical coherence tomography (OCT) in imaging intrableb morphology after trabeculectomy. Methods: 14 post-trabeculectomy eyes from 11 primary open angle glaucoma and 3 primary angle closure glaucoma subjects were studied. The blebs were classified with reference to slit lamp morphology and bleb function. They included diffuse filtering (n = 7), cystic (n = 2), encapsulated (n = 2) and flattened (n = 3) bleb types. One eye in each patient was imaged with the Visante anterior segment OCT. A vertical scan line of 10 mm consisting of 512 A-scans was positioned at the centre of the bleb. The images were then analysed by built-in software. Intrableb morphologies and structures, including bleb wall thickness, subconjunctival fluid collections, suprascleral fluid space, scleral flap thickness, intrableb intensity (low, medium or high) and the route under the scleral flap were characterised and measured. Results: Diffuse filtering blebs were found by subconjunctival fluid collections. Suprascleral fluid space and the route under the scleral flap were identified in four of the seven cases. Cystic blebs were composed of a large hyporeflective space with multiloculated fluid collections covered by a thin layer of conjunctiva. Encapsulated blebs had a thick bleb wall with high reflectivity and an enclosed fluid filled space. Flattened blebs demonstrated high scleral reflectivity and no bleb elevation. Conclusions: Visante anterior segment OCT can be used for bleb imaging. The different patterns of intrableb morphology identified by OCT were related to slit lamp appearance and bleb function. This information may be useful to study the different surgical outcomes and the process of wound healing in trabeculectomised eyes.

Evaluation of Retinal Nerve Fiber Layer Progression in Glaucoma: A Prospective Analysis with Neuroretinal Rim and Visual Field Progression

OBJECTIVE 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. DESIGN Prospective study. PARTICIPANTS One hundred eight eyes of 70 glaucoma patients. METHODS 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. MAIN OUTCOME MEASURES The agreement on progression detection and the rate of change of RNFL, neuroretinal rim, and VFI measurements. RESULTS 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%). CONCLUSIONS 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. FINANCIAL DISCLOSURE(S) Proprietary or commercial disclosure may be found after the references.