Showing papers on "Optical coherence tomography published in 1995"

Optical Coherence Tomography of the Human Retina

Abstract: Objective: To demonstrate optical coherence tomography for high-resolution, noninvasive imaging of the human retina. Optical coherence tomography is a new imaging technique analogous to ultrasound B scan that can provide cross-sectional images of the retina with micrometer-scale resolution. Design: Survey optical coherence tomographic examination of the retina, including the macula and optic nerve head in normal human subjects. Setting: Research laboratory. Participants: Convenience sample of normal human subjects. Main Outcome Measures: Correlation of optical coherence retinal tomographs with known normal retinal anatomy. Results: Optical coherence tomographs can discriminate the cross-sectional morphologic features of the fovea and optic disc, the layered structure of the retina, and normal anatomic variations in retinal and retinal nerve fiber layer thicknesses with 10-??m depth resolution. Conclusion: Optical coherence tomography is a potentially useful technique for high depth resolution, cross-sectional examination of the fundus.

Optical biopsy and imaging using optical coherence tomography.

Abstract: Optical coherence tomography is a new imaging technique that can perform high-resolution, micrometre-scale, cross-sectional imaging in biological systems. The technology has been developed, and reduced to, preliminary clinical practice in ophthalmology. The challenging problem that OCT may address is the development of 'optical biopsy' techniques. These techniques can provide diagnostic imaging of tissue morphology without the need for excision of specimens. Many investigations remain to identify optimal areas for clinical application, and additional engineering must be done to integrate vertically the technology and to reduce it to clinical practice. Nevertheless, preliminary studies indicate the feasibility of developing this technology for a wide range of clinical and research diagnostic imaging applications. The ability to non-excisionally evaluate tissue morphology using a catheter or an endoscope could have a significant impact on the diagnosis and management of a wide range of diseases.

Quantification of Nerve Fiber Layer Thickness in Normal and Glaucomatous Eyes Using Optical Coherence Tomography: A Pilot Study

Abstract: Purpose: Quantitative assessment of nerve fiber layer (NFL) thickness in normal and glaucomatous eyes, and correlation with conventional measurements of the optic nerve structure and function. Methods: We studied 59 eyes of 33 subjects by conventional ophthalmologic physical examination, Humphrey 24-2 visual fields, stereoscopic optic nerve head photography, and optical coherence tomography. Results: Nerve fiber layer thickness as measured by optical coherence tomography demonstrated a high degree of correlation with functional status of the optic nerve, as measured by visual field examination ( P =.0001). Neither cupping of the optic nerve nor neuroretinal rim area were as strongly associated with visual field loss as was NFL thickness ( P =.17 and P =.21,respectively). Cupping correlated with NFL thickness only when the cup was small (cup-to-diameter ratio, 0.1 to 0.3) or large (cup-to-diameter ratio, 0.8 to 1.0) ( P =.006); there was no correlation between cupping and NFL thickness otherwise. Nerve fiber layer, especially in the inferior quadrant, was significantly thinner in glaucomatous eyes than in normal eyes ( P =.04). Finally, we found a decrease in NFL thickness with aging, even when controlling for factors associated with the diagnosis of glaucoma ( P =.03). Conclusions: Nerve fiber layer thickness can be measured using optical coherence tomography. These measurements provide good structural and functional correlation with known parameters.

Quantitative Assessment of Macular Edema With Optical Coherence Tomography

Abstract: Objective: To evaluate optical coherence tomography, a new technique for high-resolution cross-sectional imaging of the retina, for quantitative assessment of retinal thickness in patients with macular edema. Design: Survey examination with optical coherence tomography of patients with macular edema. Setting: Referral eye center. Patients: Forty-nine patients with the clinical diagnosis of diabetes or diabetic retinopathy and 25 patients with macular edema secondary to retinal vein occlusion, uveitis, epiretinal membrane formation, or cataract extraction. Main Outcome Measures: Correlation of optical coherence tomograms with slit-lamp biomicroscopy, fluorescein angiography, and visual acuity. Results: Optical coherence tomograms of cystoid macular edema closely corresponded to known histopathologic characteristics. Quantitative measurement of retinal thickness is possible because of the well-defined boundaries in optical reflectivity at the inner and outer margins of the neurosensory retina. Serial optical coherence tomographic examinations allowed tracking of both the longitudinal progression of macular thickening and the resolution of macular edema after laser photocoagulation. In patients with diabetic retinopathy, measurements of central macular thickness with optical coherence tomography correlated with visual acuity, and optical coherence tomography was more sensitive than slit-lamp biomicroscopy to small changes in retinal thickness. Conclusions: Optical coherence tomography appears useful for objectively monitoring retinal thickness with high resolution in patients with macular edema. It may eventually prove to be a sensitive diagnostic test for the early detection of macular thickening in patients with diabetic retinopathy.

Determination of the refractive index of highly scattering human tissue by optical coherence tomography.

Abstract: We describe two new techniques, based on optical coherence tomography (OCT), for determining the refractive index of highly scattering human tissue. We obtained refractive indices of in vitro human tissue, using OCT to measure the physical and optical path lengths of the sample. We obtained measurements of the refractive index of in vitro and in vivo human tissue, using OCT to track the focal length shift that results from translating the focus along the optic axis within the tissue. The refractive indices of human skin, adipose, and muscle were measured and compared with previously published estimates.

Optical coherence tomography: a new tool for glaucoma diagnosis.

Abstract: Optical coherence tomography (OCT) is a novel technique that allows cross-sectional imaging of the anterior and posterior eye. OCT has a resolution of approximately 10 microns, with extremely high sensitivity (approximately 10(-10) of incident light). OCT is analogous to computed tomography, which uses x-rays, magnetic resonance imaging, which uses spin resonance, or B-scan ultrasound, which uses sound waves, but OCT uses only light to derive its image. OCT is a noncontact, noninvasive system by which retinal substructure may be analyzed in vivo. OCT is useful in the evaluation of retinal pathologies and glaucoma. In retinal disease, entities such as macular holes, macular edema, central serous chorioretinopathy, retinal vascular occlusion and other factors have been examined. Separation between the posterior vitreous and retina, or lack thereof, are seen and quantitated. In glaucoma, retinal nerve fiber layer (NFL) thickness is measured at standardized locations around the optic nerve head. A circular scan produces a cylindrical cross-section of the retina, from which the NFL can be analyzed. In addition, radial scans through the optic nerve head are used to evaluate cupping and juxtapapillary NFL thickness. OCT, a new imaging technology by which the anterior and posterior segment are seen in cross-section, may permit the early diagnosis of glaucoma, and the early detection of glaucomatous progression.

Optical coherence tomography corneal mapping apparatus

Abstract: Optical coherence tomography ("OCT") corneal mapping apparatus includes an OCT apparatus having a rotating helical mirror for altering a reference beam path in the OCT apparatus; a raster scanner for raster scanning sampling optical output from the OCT apparatus; a curved mirror for transferring the sampling optical output from the raster scanner to an eye and for transferring sampling optical output reflected from the eye back to the OCT apparatus through the raster scanner; and an analyzer, coupled to the raster scanner, the rotating helical mirror, and reference and sampling interaction output from the OCT apparatus. The analyzer causes the raster scanner to scan the sampling optical output to points in a raster; causes the rotating mirror to alter the length of the reference beam path over a predetermined amount at each of the points in the raster; and provides the corneal mapping from the reference and sampling interaction output at the points in the raster.

Optical coherence tomography assisted surgical apparatus

Abstract: Ophthalmologic surgical microscope which is combined internally with an optical coherence tomography ("OCT") apparatus wherein auto-focusing is provided by driving a motorized internal focusing lens of the ophthalmologic surgical microscope with a signal output from the OCT apparatus. An embodiment of the inventive ophthalmologic surgical microscope includes: (a) an optical coherence tomography ("OCT") apparatus; (b) a beamcombiner for internally coupling output from the OCT apparatus into the ophthalmologic surgical microscope; and (c) a motor for moving an internal focusing lens of the ophthalmologic surgical microscope in response to a signal from the OCT apparatus, whereby the ophthalmologic surgical microscope is auto-focused.

Quantitative Assessment of Macular Edema with Optical Coherence Tomography

Abstract: Objective: To evaluate optical coherence tomography, a new technique for high-resolution cross-sectional imaging of the retina, for quantitative assessment of retinal thickness in patients with macular edema. Design: Survey examination with optical coherence tomography of patients with macular edema. Setting: Referral eye center. Patients: Forty-nine patients with the clinical diagnosis of diabetes or diabetic retinopathy and 25 patients with macular edema secondary to retinal vein occlusion, uveitis, epiretinal membrane formation, or cataract extraction. Main Outcome Measures: Correlation of optical coherence tomograms with slit-lamp biomicroscopy, fluorescein angiography, and visual acuity. Results: Optical coherence tomograms of cystoid macular edema closely corresponded to known histopathologic characteristics. Quantitative measurement of retinal thickness is possible because of the well-defined boundaries in optical reflectivity at the inner and outer margins of the neurosensory retina. Serial optical coherence tomographic examinations allowed tracking of both the longitudinal progression of macular thickening and the resolution of macular edema after laser photocoagulation. In patients with diabetic retinopathy, measurements of central macular thickness with optical coherence tomography correlated with visual acuity, and optical coherence tomography was more sensitive than slit-lamp biomicroscopy to small changes in retinal thickness. Conclusions: Optical coherence tomography appears useful for objectively monitoring retinal thickness with high resolution in patients with macular edema. It may eventually prove to be a sensitive diagnostic test for the early detection of macular thickening in patients with diabetic retinopathy.

Gaze tracking using optical coherence tomography

Abstract: Apparatus for gaze tracking an eye utilizing short coherence length interferometry, also known as optical coherence tomography ("OCT"). An embodiment of the present invention is an apparatus for gaze tracking an eye which includes: (a) an optical coherence tomography (OCT) apparatus; (b) a scanning apparatus for scanning across a predetermined portion of the eye with optical output from the OCT apparatus; (c) an analysis apparatus for analyzing detection signals output from the OCT apparatus to determine a location of a feature of the eye; (d) an illumination apparatus for producing a reflection of radiation from a cornea of the eye (corneal reflex); (e) a detection apparatus for determining a location of the corneal reflex; and (f) the analysis apparatus further includes an apparatus which is responsive to the location of the feature and to the location of the corneal reflex for gaze tracking.

Optical coherence tomography for ophthalmic imaging: new technique delivers micron-scale resolution

Abstract: The authors have developed a new technique for micron scale resolution cross-sectional imaging of ocular and other biological tissue, called optical coherence tomography (OCT). OCT is similar to B-scan ultrasonic imaging, except that image contrast relies on differences in optical rather than acoustic backscattering characteristics of tissue. In contrast to ultrasound and nonlinear optical gating techniques, low-coherence interferometry is used to resolve the position of reflective or optical backscattering sites within a sample. Two-dimensional tomographic images of a thin, optical slice of tissue may be obtained with 10 /spl mu/m longitudinal and lateral resolution. Optical heterodyne detection and the application of noise-reduction techniques originally developed for optical communication achieve sensitivity to reflected light as small as 10/sup -10/ of the incident optical power. OCT is non-contact, non-invasive, and has superior resolution to conventional clinical ultrasound. Unlike scanning laser ophthalmoscopy and scanning laser tomography, the optical sectioning capability of OCT is not limited by the pupil aperture and ocular aberrations. OCT may be implemented in a compact, low-cost, fiber-optic based interferometer that is easily coupled to existing ophthalmic instrumentation. Here, the authors demonstrate high-speed in vivo OCT imaging in both the anterior and posterior eye, and highlight the system's potential usefulness for the early diagnosis and quantitative monitoring of a variety of ocular diseases and treatments. >

In vivo imaging of the development of linear and nonlinear retinal laser effects using optical coherence tomography in correlation with histopathological findings

Abstract: Optical Coherence Tomography (OCT) is a new, non-invasive diagnostic technique for high resolution optical 3D imaging, which was developed and applied to several different biological materials during the lasi; five years [1, 2, 3]. A unique application ofthis technique is the microscopical cross-sectional imaging ofpostenor structures ofthe eye which are not accessable with other high resolution techniques in-vivo neither with x-ray-imaging nor with high frequency ultrasound scanning. The superior spatial resolution on the order ofabout lOtm laterally and axially, the high signal-to-noise ratio ofmore than 100 db and the fast acquisition-time of one second for a two dimensional scan provides a technique for cross-sectional in-vivo-momtoring ofintraocular structures and therefore the possibility to study the time course of anatomical and pathological developments in the eye. The acute morphological changes of ocular structures and their biological healing response after shortterm impacts such as high-intensity laser exposures are ofparticular interest for the understanding of the mechanisms responsible for therapeutic laser-application in ophthal-mology as well as for laser injury to the eye. A correlation between cross-sectional OCT-images and structural findings using classical histopathological techniques facilitates a better interpretation ofthe characteristic patterns seen in OCTimages and defines the sensitivity ofthe OCT-technique to image morphological details. On the other hand preparational artefacts not avoidable in all histological procedures can be identified and analyzed by comparing histological micrographs with OCT-images of exactly the same structure. First results of an experimental study where retinal effects were produced in monkey eyes using laser pulses from 200 ms to 130 fs in duration are presented in this article. The applied energies from 5tJ to 50 mJ were able to induce the whole spectrum of biological effects possible in the eye, ranging from intraretinal microruptures to extensive thermal denaturation and massive preretinal hemorrhages [4, 5, 6].

Optical coherence tomography (OCT) of human skin with a slow-scan CCD camera

Abstract: The purpose of this research is to investigate and improve the possibilities of optical coherence tomography for evaluation and imaging of the skin structure and dermatological diseases as melanoma. Single point detection, as done with a photodiode on the human eye was not successful in reaching high resolutions in strong scattering media as the skin. Therefore, an experimental setup with a very sensitive slow-scan CCD-camera and a suitably adapted interferometric arrangement was built. Measurements were performed on models and ex vivo biological material up to a depth of 2 mm. Developments concerning a specially shaped fast detector head with on-line analogue data processing are presented.

In vivo optical coherence tomography and topography of the fundus of the human eye

Abstract: The dual beam scanning partial coherence interferometry technique, which was recently developed to measure the fundus profile of the human eye in vivo, is used for tomographic and topographic imaging and for the measurement of different retinal structures, e.g., the contour of the papilla and thickness profiles of retina and retinal nerve fiber layer. In case of well defined, sharp boundaries between two layers of different refractive indices, the absolute position of these retinal structures can be determined with a precision (standard deviation) of 5 micrometers . Compared to first results with this instrument, the measurement time for horizontal and vertical scans was reduced by a factor of 10. At present, the measuring time of a vertical scan over 10 degree(s) in steps of 0.5 degree(s) takes at least 20 seconds without and 80 seconds with signal averaging of 4 longitudinal scans over 1.5 mm distance. Further improvements to 5 - 20 seconds are discussed. The longitudinal resolution of this instrument is approximately 15 micrometers (full-width-half-maximum), depending on the coherence length of the light source; this is about 5 times better than previous measurements. Topographic and tomographic scans across the optic disk reveal an increase of thickness of the retinal nerve fiber layer at the inferior and superior rim of the disk, which are in good agreement with results published in the literature.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical coherence tomography in multiply scattering tissue

Abstract: Optical Coherence Tomography (OCT) is a new technique that is used to obtain cross- sectional images of highly scattering tissue. OCT has been applied to image both architectural and cellular morphologic structures in clinically relevant in vitro human tissues, including the human epiglottis and full-thickness skin. The performance of OCT at 850 nm and 1300 nm is compared. In addition, high numerical aperture OCT enhanced confocal microscopy have potential for non-invasive in vivo diagnosis.

New noninvasive imaging technique for cataract evaluation in the rhesus monkey

Abstract: We present the first in vivo study using Optical Coherence Tomography (OCT) as the imaging device for lenticular cataracts in the geriatric rhesus monkey. OCT is a non-invasive imaging technique that produces a 2D cross sectional image of intraocular tissue similar to ultrasound B scan. In OCT the images are formed by measuring optical reflections from the tissue. Eighteen geriatric subjects with documented lenticular opacities and one control subject were imaged. The OCT images produced are compared to current and previous clinical cataract grading exams and slit-lamp photography. Histopathology was collected on one subject and is compared to the OCT image. OCT provides information on nuclear, cortical and subcapsular opacities. The image formation is presented based on a color coded computer generated log reflective scale. The log reflective scale is converted to a qualitative grading system. Although movement and shadow artifact can occur, these are readily identifiable and can be differentiated from underlying lenticular abnormalities. OCT has great potential to assist in further characterization of cataracts.

Time-gated holographic imaging using photorefractive media

Abstract: A depth-resolved imaging system is described for recording three dimensional images of objects embedded in diffuse media. Time-gated holographic imaging, employing rhodium- doped barium titanate as the recording medium, is used to obtain whole-field depth-resolved two dimensional images. Infra-red radiation has been used which corresponds to the medical imaging window, as well as blue radiation which may be suitable for undersea imaging.