Biomedical subjects

Jarbas C Castro

Publications and source records attributed to Jarbas C Castro.

4 recordsLinked to original sources

PubMed2006

Retinal assessment using optical coherence tomography.

Over the 15 years since the original description, optical coherence tomography (OCT) has become one of the key diagnostic technologies in the ophthalmic subspecialty areas of retinal diseases and glaucoma. The reason for the widespread adoption of this technology originates from at least two properties of the OCT results: on the one hand, the results are accessible to the non-specialist where microscopic retinal abnormalities are grossly and easily noticeable; on the other hand, results are reproducible and exceedingly quantitative in the hands of the specialist. However, as in any other imaging technique in ophthalmology, some artifacts are expected to occur. Understanding of the basic principles of image acquisition and data processing as well as recognition of OCT limitations are crucial issues to using this equipment with cleverness. Herein, we took a brief look in the past of OCT and have explained the key basic physical principles of this imaging technology. In addition, each of the several steps encompassing a third generation OCT evaluation of retinal tissues has been addressed in details. A comprehensive explanation about next generation OCT systems has also been provided and, to conclude, we have commented on the future directions of this exceptional technique.

Anatomy, Cross-Sectional↗

PubMed2006

The placido wavefront sensor and preliminary measurement on a mechanical eye.

PURPOSE: The hardware and software of a novel wavefront sensor was developed (The sensor presented here is patent pending.). It has the same principal of the Hartmann-Shack (HS) and other sensors that are based on slope information for recovery of wavefront surface, but a different symmetry, and does not use individual microlenses. This polar symmetry might offer differences during practical measurements that may add value to current and well-established "gold standard" techniques. METHODS: The sensor consists of a set of concentric "half-donut" surfaces (longitudinally sectioned toroids) molded on an acrylic surface with a CCD located at the focal plane. When illuminated with a plane wavefront, it focuses a symmetric pattern of concentric discs on the CCD plane; for a distorted wavefront, a nonsymmetric disc pattern is formed (similar to images of a placido-based videokeratographer). From detection of shift in the radial direction, radial slopes are computed for a maximum of 2880 points, and the traditional least-squares procedure is used to fit these partial derivatives to a set of 15 conventional OSA-VSIA Zernike polynomials. Theoretical computations for several synthetic surfaces containing low-order aberration (LOA) and high-order aberration (HOA) were implemented for both the HS and the new sensor. RESULTS: Root mean square error (RMSE) in microns when theoretical data was taken as control, for HS sensor and new sensor, was 0.02 and 0.00003 for LOA (defocus, astigmatism) and 0.07 and 0.06 for HOA (coma, spherical, and higher terms), respectively. After this, practical preliminary measurements on a mechanical eye with a 5-mm pupil and 10 different defocus aberrations ranging from -5 D to 5 D, in steps of 1 D, were compared between sensors. RMSE for difference in measurements for HS and new sensor for sphere, cylinder, and axis, was 0.13 D, 0.07 D, and 11. Measurements were taken only on defocus aberrations. Qualitative images for astigmatism are shown. DISCUSSION: Although practical in vivo tests were not conducted in this first study, we also discuss certain possible alignment differences that may arise as a result of the different symmetry of the new sensor. To take any conclusive assumption regarding the accuracy and/or precision of this new sensor, when compared with other well-established sensors, statistically significant in vivo measurements will need to be conducted.

Cornea↗

PubMed2005

Occult chorioretinal anastomosis in age-related macular degeneration: a prospective study by optical coherence tomography.

PURPOSE: To investigate macular optical coherence tomography (OCT) features in patients with chorioretinal anastomosis (CRA) and drusen, as well as their correlation with the Gass occult-CRA hypothesis. DESIGN: Prospective observational case series. METHODS: setting: Tertiary ophthalmic referral center. study population: All patients with biomicroscopic evidence of CRA and drusen consecutively evaluated between February 2003 and March 2004. observation procedures: Third-generation OCT evaluation and stereoscopic angiographic studies. main outcome measures: Macular morphologic features at baseline and at 12 weeks. RESULTS: Twenty eyes with CRA and drusen were identified in 11 patients, seven women (63.6%) and four men (36.4%) ranging in age from 69 to 82 years (median, 79 years). Focal elevation of the retinal pigment epithelium was seen in eyes with stage 1 (pre-clinical) CRA. Small hyperreflective signals at the level of the elevated retinal pigment epithelium were seen in stage 2 CRA. In stage 3 CRA, a hyperreflective "mound" at the level of the elevated retinal pigment epithelium was seen in association with a thickened retina. In stage 4 CRA sub-retinal pigment epithelium fluid accumulation was present, and complete disorganization of the macular region was observed in stage 5 CRA. Macular changes were observed in eight eyes (40%) at follow-up, with all but one CRA lesion progressing one stage. CONCLUSION: Morphologic features and changes demonstrated by OCT suggest that fibrovascular detachment of the retinal pigment epithelium followed by development of occult CRA are the initial events occurring in eyes with CRA in age-related macular degeneration. Our findings may support the evolutionary CRA staging system proposed by Gass.

Aged↗

PubMed2004

Optical coherence tomography 3: Automatic delineation of the outer neural retinal boundary and its influence on retinal thickness measurements.

PURPOSE: To investigate the automatic delineation of the outer limits of the macular neural retina, by using the optical coherence tomography (OCT)-3 built-in software, and to determine its influence in assessing retinal thickness in the normal macula. METHODS: Retrospective analysis of the OCT3 data at a tertiary-care referral center was performed to study the automatic delineation of the outer neural retina boundary generated by the OCT built-in software. In parallel, a cross-sectional study was designed to compare retinal thickness measurements obtained at specific macular regions of nine normal eyes by the automatic measurement tool with those obtained using a manual-caliper-assisted technique. RESULTS: OCT data from 121 eyes were evaluated. Two parallel, linear highly reflective layers (HRL) were visible at the level of the outer retinal boundary in normal macular regions. Disappearance of the inner and maintenance of the outer HRL was noted in the presence of eye conditions affecting the external retinal layers. The automated software delineation for the outer retinal border was primarily guided by the presence of the inner HRL, whereas the correlation of the OCT findings with the expected clinical and angiographic features on eyes presenting specific macular conditions pointed toward a deeper retinal pigment epithelium-retina interface occurring at the level of the outer HRL. There was a statistically significant difference between the retinal thickness in specific normal macular regions obtained by the automatic measurement tool and the caliper-assisted technique in which the outer retinal border delineation was based on the outer HRL (P = 0.008, Wilcoxon signed rank test). CONCLUSIONS: Incorrect delineation of the outer neural retina boundary is occurring with the automated retinal thickness measurement tool of the OCT3 software. At specific regions of the normal macula, retinal thicknesses were significantly underestimated due to such misalignment.

Adolescent↗