![]() ![]() To be included in this study, images had to be at least 6 out of 10 in intensity and taken as close to the fovea as possible, by choosing to image the thinnest point of the macula, with the understanding that slight differences in positioning could affect the measured thicknesses. The images were taken in the usual manner and were not inverted to bring the choroid in closer proximity to the zero delay line, as image inversion using the Cirrus software results in a low resolution, pixilated image. The 1 line raster is a 6 mm line consisting of 4096 A-scans. Cirrus HD-OCT scans were obtained from patients as part of a comprehensive dilated ophthalmological exam, as well as from undilated healthy volunteers with no visual complaints or history of ocular pathology. ![]() Patients with a myopic refractive error of greater than minus 6.0 diopters were excluded from this study. Medical chart review was done to identify patients with no retinal or choroidal pathology. Decreased signal strength posterior to the RPE is compensated by this image enhancement software which enables visualization of the border where choroidal tissue meets sclera and allows choroidal thickness measurements to be performed.Ī retrospective analysis was performed on 34 eyes of 34 normal patients, who underwent high definition 1 line raster scanning at the New England Eye Center, Tufts Medical Center, Boston, MA between November and December 2009. This processing software is comparable to frame averaging, but unique in that images are generated by evaluating all of the pixel data to reduce noise and construct the best possible image. Selective pixel profiling™ available in the newest version 4.5 software generates high definition 1 line raster image from 20 B-scans taken at a single location. Previously, the full thickness of the choroid could not be seen in most eyes due to scattering and insufficient light penetration beyond the retinal pigment epithelium (RPE), as well as, signal strength roll-off distal to the zero-delay line. The SD Cirrus HD-OCT light source is centered on 800 nm wavelength, achieving 5 μm axial resolution in tissue. 16 The aim of this study was to evaluate another commercially available spectral domain device, Cirrus-HD OCT (Carl Zeiss Meditec, Inc., Dublin, CA) to see if its new software, which permits acquisition of 20 B-scans simultaneously in a single raster line scan, would allow accurate measurement of choroidal thickness and area in normal eyes using previously proposed measurement techniques. 10 - 15 Ikuno et al have recently characterized normal choroidal thickness in Japanese subjects using a 1060 nm based light source. ![]() OCT imaging with longer wavelengths at 1060 nm (compared to 800 nm used in commercial OCT systems) has also been shown to increase signal penetration into the choroid and optic nerve head. Since spectral domain detection has highest sensitivity near zero-delay and sensitivity decreases for larger delays, by doing this, the choroid is closer to the zero-delay line, providing enhanced sensitivity and increased imaging depth. Furthermore, Spaide demonstrated the ability of the spectral domain (SD) OCT systems to show an inverted OCT image by moving the device close to the patients’ eye. 2 - 7 The Spectralis offers eye tracking technology and the capability to capture up to 100 B-scans in the same position for OCT signal averaging 8, 9 and enhancement. Spaide et al recently reported the successful examination and measurement of choroidal thickness in normal and pathological states using the Heidelberg Spectralis (Heidelberg Engineering, Heidelberg, Germany) OCT instrument. The choroid plays a vital role in the pathophysiology of many diseases affecting the retina but adequate visualization of the choroid using OCT has not been possible until recently. With advancements in OCT image processing software, more refined details of the posterior segment can be appreciated and characterized in vivo. The introduction of optical coherence tomography 1 (OCT) into clinical practice has changed ophthalmology, and with progression of new technology, the ability to obtain a true, non-invasive “optical biopsy” of the posterior segment is almost achievable. ![]()
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