Humberto Ruiz-Garcia

Spatial distribution of posterior pole choroidal thickness by spectral domain optical coherence tomography.

PURPOSE To study the spatial distribution of posterior pole choroidal thickness (CT) in healthy eyes using spectral domain optical coherence tomography (SD-OCT). METHODS Fifty-nine eyes from 30 subjects with no retinal or choroidal disease were examined with high-definition (HD) OCT using macular volume cube scanning protocols. A randomly chosen subset also had multifield analysis performed (volume scans centered on and surrounding the optic nerve head [ONH]). CT was manually quantified using a validated reading center tool. For macular scans, mean CT was calculated for each Early Treatment Diabetic Retinopathy Study subfield. Compound posterior pole CT maps were also created through the alignment of OCT projection images. Regression analyses were used to evaluate the correlation between CT and axial length (AL), refractive error, age, sex, and ethnicity. RESULTS Subfoveal CT was 297.8 ± 82.2 μm, which did not differ significantly from that of the inner macular subfields. CT was greatest in the superior outer subfield and thinnest in the nasal outer subfield. The most predictive models for macular CT included AL and/or age. Outside the macula, CT was thinnest inferonasal to the ONH. CONCLUSIONS CT demonstrates large variations between individuals, but also at different locations within the posterior pole; substantial choroidal thinning inferonasal to the ONH was demonstrated. CT appears to correlate more with distance from the optic nerve than from the fovea and, thus, in future studies, the ONH may serve as a better reference point than the foveal center for expressing or depicting regional CT variations.

Automated characterization of pigment epithelial detachment by optical coherence tomography.

PURPOSE To assess the accuracy of automated classification of pigment epithelial detachments (PED) by using a software algorithm applied to spectral-domain optical coherence tomography (SD-OCT) scans. METHODS HD-OCT (Cirrus; Carl Zeiss Meditec, Dublin, CA) volume scans (512 × 128) were retrospectively collected from 46 eyes of 33 patients with evidence of PED in the setting of age-related macular degeneration (AMD, n = 28) or central serous chorioretinopathy (CSCR, n = 5). In these eyes, 168 PEDs were automatically detected with a system-associated tool (Cirrus HD-OCT RPE Elevation Analysis; Carl Zeiss Meditec). Two independent, certified Doheny Image Reading Center (DIRC) OCT graders classified these PEDs into three categories--serous, drusenoid, or fibrovascular--via inspection of the B-scans. Manual classification results served as the gold standard for comparisons with automated classification. For automated classification, interindividual variation in intensities was normalized in all images. Individual A-scans within the detected PEDs were then automatically classified into one of three categories based on the mean internal intensity and the standard deviation of the internal intensity: mean intensity <30 (serous type); mean intensity ≥30 but <60 or mean intensity ≥30 and SD ≥30 (fibrovascular type); or mean intensity ≥60 and SD < 30 (drusenoid type). Individual PEDs were then automatically classified into the same three categories based on the predominant type of A-scan within the PED. For mixed PEDs (many A-scans of each type), a risk index for neovascularization was computed based on the percentage of fibrovascular A-scans. In addition, a confidence index was computed for each PED based on its mathematical distance from the PED category boundaries. RESULTS Among the 168 PEDs, the DIRC graders classified 16 as serous, 88 as fibrovascular, and 64 as drusenoid PEDs. The automated algorithm classified 14 as serous, 96 as fibrovascular, and 58 as drusenoid PEDs. The sensitivity and specificity values for automated classification according to type of PED were 88% and 100% for serous, 76% and 64% for fibrovascular, and 58% and 81% for drusenoid, respectively. CONCLUSIONS Automated classification of PEDs using internal reflectivity characteristics appears to be sensitive for detecting serous and fibrovascular PEDs. Automated classification and quantification of PEDs may be a useful tool in future studies for stratifying PEDs according to risk and possibly predicting the risk of advanced AMD.

Comparison of manually corrected retinal thickness measurements from multiple spectral-domain optical coherence tomography instruments

Background/aims To compare retinal thickness measurements from three different spectral domain optical coherence instruments when manual segmentation is employed to standardise retinal boundary locations. Methods 40 eyes of 21 healthy subjects were scanned on the Cirrus HD-OCT, Topcon 3D-OCT-2000 and Heidelberg Spectralis-OCT. Raw data were imported into custom grading software (3D-OCTOR). Manual segmentation was performed on every data set, and retinal thickness values in the foveal central subfield were computed. Results 37 eyes of 20 subjects were gradable on every machine. The average retinal thicknesses for these eyes were 236.7 μm (SD 20.1), 235.7 μm (SD 20.4) and 236.5 μm (SD 18.0) for the Cirrus, 3D-OCT-2000 and Spectralis, respectively. Comparing manual retinal thickness measurements between any two machines, the maximum difference was 18.2 μm. The mean absolute differences per eye between two machines were: 4.9 μm for Cirrus versus 3D-OCT-2000, 3.7 μm for Cirrus versus Spectralis and 4.4 μm for 3D-OCT-2000 versus Spectralis. Conclusions When a uniform position is used to locate the outer retinal boundary, the retinal thickness measurements derived from three different spectral domain optical coherence instruments devices are virtually identical. Manual correction may allow OCT-derived thickness measurements to be compared between devices in clinical trials and clinical research.

Accuracy and reproducibility of automated drusen segmentation in eyes with non-neovascular age-related macular degeneration.

PURPOSE To evaluate the accuracy and reproducibility of drusen quantification by an automated drusen segmentation algorithm in spectral domain optical coherence tomography (SD-OCT) images of eyes with non-neovascular age-related macular degeneration (AMD). METHODS Drusen segmentation was performed using both a commercial automated algorithm (Cirrus OCT RPE analysis tool) and manual segmentation in 44 eyes of 30 subjects with dry AMD who underwent volume OCT scanning. The drusen (space between outer RPE layer and Bruchs membrane) was segmented automatically using an automated RPE tool and manually by 3D-OCTOR software. Drusen area and volume were calculated in all eyes. Age and visual acuity data were also collected. Reproducibility of manual and automated measurements was assessed by intraclass correlation (ICC). RESULTS The mean age of subjects was 78.24 (± 9.4; range, 56-97 years). The mean logMAR (logarithm of the minimum angle of resolution) visual acuity was 0.4 (Snellen equivalent, ~20/50) (standard deviation, 0.40; range, 0-1.3). The mean (standard deviation) drusen area was 5.05 (3.67) mm(2) with manual segmentation and 4.66 (3.51) mm(2) with the automated RPE tool; the absolute difference was 2.63 (2.5) mm(2). The mean drusen volume was 1.49 (0.42) mm(3) with manual segmentation and 1.42 (0.43) mm(3) with the automated RPE tool; the absolute difference was 1.42 (0.43) mm(3). The agreement between manual and automated measurements of drusen volume (highest ICC = 0.95) was better than the agreement for drusen area (ICC = 0.65). CONCLUSIONS The quantification of drusen area and volume using an automated RPE yielded better agreement for volume than for area when compared with human expert manual segmentation. Using this software, drusen volume measurements may be a useful tool for quantifying drusen burden in clinical trials and clinical practice.

Clinical Applications of Long-Wavelength (1,000-nm) Optical Coherence Tomography

Commercial optical coherence tomography (OCT) instruments generally use light sources in the range of 800 to 860 nm. Although imaging with these light sources provides excellent visualization of the retinal architecture, details of structures and abnormalities below the retinal pigment epithelium are often limited. At the same time, the optimal light source wavelength for clinical OCT imaging is unknown. OCT imaging using longer wavelength light (1,050 nm) has several potential advantages, including less scattering with media opacity and deeper penetration. This article reviews the current state-of-the-art of long wavelength OCT imaging and explores potential clinical applications.

Impact of scanning density on spectral domain optical coherence tomography assessments in neovascular age-related macular degeneration

Purpose:  To determine the effect of optical coherence tomography (OCT) B‐scan density on the qualitative assessment of neovascular age‐related macular degeneration (AMD).

Effect of angle of incidence on macular thickness and volume measurements obtained by spectral-domain optical coherence tomography.

PURPOSE Evaluation of the effect of angle of incidence on macular thickness and volume measurements obtained by spectral-domain optical coherence tomography (OCT). METHODS A total of 30 eyes from 15 healthy young subjects underwent macular cube volume scans (512 × 128 protocol) following dilation using the Cirrus spectral domain OCT. For each eye, scans were obtained by positioning the scanning beam in the center of the dilated pupil, as well as in four eccentric positions (approximately 3 mm from the center), superior, inferior, nasal, and temporal to the pupillary center, to create oblique angles of incidence between the light beam and retina. In all cases, the region scanned by the volume cube was centered on the fovea. Macular thickness and volume measurements were computed for volume scan acquisitions, and differences in values between eccentric scans and the central scan were analyzed. RESULTS Retinal thickness and volume values were observed to increase significantly in all subfields for all eccentrically-obtained scans compared to scans obtained through the center of the pupil. The mean increase in thickness for the various scan positions and subfields ranged from 3.76 to 11.38. Scans that were displaced temporally consistently showed the greatest increase in thickness and volume, whereas nasally positioned scans showed the least increase. The increase in retinal thickness for all subfields correlated significantly with angle of inclination or tilting of the retina. CONCLUSIONS Macular thickness and volume measurement results may be affected significantly by positioning of the scanning beam in the pupil and resultant angle of incidence on the retina. These findings suggest that care should be taken to position the scanning beam consistently in the center of the pupil to achieve reliable measurements.