Effect of Optical Coherence Tomography Scan Decentration on Macular Center Subfield Thickness Measurements
ABSTRACT PURPOSE: To investigate the effect of optical coherence tomography macular grid displacement on retinal thickness measurements. METHODS: SD-OCT macular scans of 66 eyes with various retinal thicknesses were selected. Decentration of the 1,3,6 mm-diameter macular grid was simulated by manually adjusting the distance between center of the fovea (cFovea) and center of the grid (cGrid). Center subfield thickness (CSF) between the internal limiting membrane and the top of the retinal pigment epithelium was measured along the displacement distance where the grid was displaced in 8 cardinal directions from the cFovea in steps of 100 μm within the central 1 mm subfield and then by 200 μm within the inner subfields. One-way/mixed-effects repeated-measures ANOVA models were used to determine changes of CSF (ΔCSF) as a function of displacement distance (for α = 0.05, power = 0.80 and effect size=0.1). The interaction between the displacement distance and direction, center point thickness (CPT), and foveal contour were also analyzed. RESULTS: The overall CSF measurement showed statistically significant error when the displacement distance between cFovea and cGrid exceeded 200 µm. The direction of displacement did not affect the ΔCSF-distance relationship, while the CPT and foveal contour significantly affected the relationship, in that some subgroups showed slightly larger tolerance in the displacement distance up to 300 µm before reaching significant CSF. CONCLUSIONS: Small displacement distances of the macular grid from the cFovea affect CSF measurements throughout a broad range of thicknesses and retinal contour alterations from disease. Accurate registration of OCT scans or post hoc re-positioning of the grid is essential to optimize CSF accuracy.
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ABSTRACT: To evaluate the repeatability and reproducibility of retinal thickness measurements in exudative age-related macular degeneration (AMD) using Stratus optical coherence tomography (OCT) (Carl Zeiss Meditec, Inc., Dublin, CA). Prospective, observational case series. A total of 200 eyes of 200 subjects with exudative AMD. Macular thickness and fast macular thickness programs of Stratus OCT were performed twice by the same examiners or 2 different examiners. The sequence of examiners was randomized 1:1:1:1. The variability of 1-mm subfield central retinal thickness (CRT), center point thickness (CPT), and retinal volume (RV) was calculated. Interobserver and intraobserver variability of retinal thickness measurements. Ninety-nine patients/eyes were enrolled in study arm 1 (repeated by the same examiner), and 101 patients/eyes were enrolled in study arm 2 (repeated by different examiners). Values of CPT, CRT, and RV were well correlated (interclass correlation coefficient, 0.71-0.93) in both study arms, revealing better results for the macular thickness program than for the fast macular thickness program. Threshold algorithm line failures were significantly correlated to the absolute differences of 2 repeated measurements for CPT, CRT, and RV but not with manually corrected maximum retinal thickness (MRT). Maximum retinal thickness was significantly influenced by the examiner performing the measurement. Age, lesion composition, examiner performing OCT examination, and sequence of examination had no significant influence. The repeatability and reproducibility of retinal thickness measurements were high, presenting better results for CRT and RV versus CPT, and for the macular thickness program versus the fast macular thickness program. The reliability of retinal thickness measurement was most frequently affected by algorithm line failures and fixation problems. A possible solution may be manually corrected measurement, such as MRT.Ophthalmology 08/2010; 117(8):1577-84. DOI:10.1016/j.ophtha.2010.04.032 · 6.17 Impact Factor
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ABSTRACT: Assess the 12-month efficacy and safety of intraocular injections of 0.3 mg or 0.5 mg ranibizumab in patients with macular edema after central retinal vein occlusion (CRVO). Prospective, randomized, sham injection-controlled, double-masked, multicenter clinical trial. We included 392 patients with macular edema after CRVO. Eligible patients were randomized 1:1:1 to receive 6 monthly intraocular injections of 0.3 mg or 0.5 mg of ranibizumab or sham injections. After 6 months, all patients with BCVA ≤20/40 or central subfield thickness ≥250 μm could receive ranibizumab. Mean change from baseline best-corrected visual acuity (BCVA) letter score at month 12, additional parameters of visual function, central foveal thickness (CFT), and other anatomic changes were assessed. Mean (95% confidence interval) change from baseline BCVA letter score at month 12 was 13.9 (11.2-16.5) and 13.9 (11.5-16.4) in the 0.3 mg and 0.5 mg groups, respectively, and 7.3 (4.5-10.0) in the sham/0.5 mg group (P<0.001 for each ranibizumab group vs. sham/0.5 mg). The percentage of patients who gained ≥15 letters from baseline BCVA at month 12 was 47.0% and 50.8% in the 0.3 mg and 0.5 mg groups, respectively, and 33.1% in the sham/0.5 mg group. On average, there was a marked reduction in CFT after the first as-needed injection of 0.5 mg ranibizumab in the sham/0.5 mg group to the level of the ranibizumab groups, which was sustained through month 12. No new ocular or nonocular safety events were identified. On average, treatment with ranibizumab as needed during months 6 through 11 maintained the visual and anatomic benefits achieved by 6 monthly ranibizumab injections in patients with macular edema after CRVO, with low rates of ocular and nonocular safety events. After sham injections for 6 months, treatment with ranibizumab as needed for 6 months resulted in rapid reduction in CFT in the sham/0.5 mg group to a level similar to that in the 2 ranibizumab treatment groups and an improvement in BCVA, but not to the same level as that in the 2 ranibizumab groups. Intraocular injections of ranibizumab provide an effective treatment for macular edema after CRVO. Proprietary or commercial disclosure may be found after the references.Ophthalmology 06/2011; 118(10):2041-9. DOI:10.1016/j.ophtha.2011.02.038 · 6.17 Impact Factor
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ABSTRACT: To characterize the types and frequencies of image artifacts associated with macular scanning using 2 common spectral-domain optical coherence tomography (SD OCT) instruments and to evaluate the impact of artifacts on foveal thickness measurements. Retrospective, observational chart review. For the Cirrus HD-OCT (Carl Zeiss Meditec, Dublin, CA), scans of 98 eyes from 58 patients were included in the study. For the Spectralis HRA+OCT (Heidelberg Engineering, Heidelberg, Germany), scans of 88 eyes from 54 patients were included. Macular volume scans of healthy and diseased eyes were evaluated systematically for image artifacts within each scan overall and within the center 1-mm area. The frequency of each artifact type was compared for scans stratified by diagnosis category. Artifacts in the center 1-mm area were graded for severity and were corrected manually using each instrument's software. Artifacts that resulted in errors of more than 50 microm or more than 10% of retinal thickness or that caused a misdiagnosis of macular edema or retinal thinning were defined as clinically significant and were analyzed further. Overall frequency of image artifacts by artifact type, relative frequency of artifacts in scans stratified by posterior segment disease diagnosis, and retinal thickness measurements of the center 1-mm subfield before and after artifact corrections. For Cirrus, 84.7% of scans had artifacts and 32.7% had at least 1 artifact in the center 1-mm area of the scan. For Spectralis, 90.9% of scans had at least 1 artifact, and 37.5% had at least 1 artifact in the center 1-mm area. Certain artifact types were observed more frequently with specific disease states. Clinically significant artifacts involving the center 1-mm area were seen in 5.1% of Cirrus and 8.0% of Spectralis scans. Image artifacts in SD OCT volume scanning are common and frequently involve segmentation errors. Artifacts are relatively less common in the center 1-mm area of scans, but may affect retinal thickness measurements in a clinically significant manner. Careful review of scans for artifacts is important when using SD OCT images and retinal thickness measurements in patient care or clinical trials.Ophthalmology 02/2010; 117(6):1177-1189.e4. DOI:10.1016/j.ophtha.2009.10.029 · 6.17 Impact Factor