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At least 469 records · Page 26Linked to original sources
PubMed1998

Calcium signals monitored from leopard frog optic tectum after the optic nerve has been selectively loaded with calcium sensitive dye.

We loaded adult leopard frog optic nerves with the calcium-sensitive dye Calcium Green-1 3000 mw dextran conjugate. The dye was transported to the optic tectum in approximately 6 days and selectively labeled optic nerve terminals as seen with confocal microscopy. Viewed with an intensified CCD system, electrical stimulation of the optic nerve in vitro increases Calcium Green-1 fluorescence significantly. With increasing number of pulses in pulse trains there was increased presynaptic facilitation as measured by increased fluorescence. Addition of nicotine to the bathing solution increased baseline fluorescence. These results suggest that Calcium Green-1 dextran conjugate can be actively transported in adult nerve fibers over a significant distance and is retained in presynaptic terminals in a form that allows monitoring of presynaptic calcium levels.

Animals↗
PubMed2003

Activation of epidermal growth factor receptor signals induction of nitric oxide synthase-2 in human optic nerve head astrocytes in glaucomatous optic neuropathy.

Glaucoma is an optic neuropathy that is associated with elevated intraocular pressure in most patients. We have previously demonstrated that the mechanism by which pressure damages optic nerve axons involves excessive nitric oxide generated by inducible nitric oxide synthase (NOS-2). We have now found that activation of the epidermal growth factor receptor (EGFR) induces NOS-2 in astrocytes of the human optic nerve head (ONH) in vitro and EGFR is significantly upregulated and tyrosine phosphorylated in reactive astrocytes in human glaucomatous ONHs in vivo. Furthermore, in response to elevated hydrostatic pressure, EGFR rapidly becomes phosphorylated in the nucleus. This pressure-dependent activation of EGFR is necessary for NOS-2 induction. Our results suggest that activation and nuclear localization of EGFR may be needed for induction of NOS-2 in response to elevated intraocular pressure in glaucomatous optic neuropathy. Identification of this key signaling pathway provides new therapeutic approaches to pharmacological neuroprotection for glaucoma.

Adult↗
PubMed1993

The effect of corticosteroids for acute optic neuritis on the subsequent development of multiple sclerosis. The Optic Neuritis Study Group.

BACKGROUND: Optic neuritis is often the first clinical manifestation of multiple sclerosis, but little is known about the effect of corticosteroid treatment for optic neuritis on the subsequent risk of multiple sclerosis. METHODS: We conducted a multicenter study in which 389 patients with acute optic neuritis (and without known multiple sclerosis) were randomly assigned to receive intravenous methylprednisolone (250 mg every six hours) for 3 days followed by oral prednisone (1 mg per kilogram of body weight) for 11 days, oral prednisone (1 mg per kilogram) alone for 14 days, or placebo for 14 days. Neurologic status was assessed over a period of two to four years. The patients in the first group were hospitalized for three days; the others were treated as outpatients. RESULTS: Definite multiple sclerosis developed within the first two years in 7.5 percent of the intravenous-methyl-prednisolone group (134 patients), 14.7 percent of the oral-prednisone group (129 patients), and 16.7 percent of the placebo group (126 patients). The adjusted rate ratio for the development of definite multiple sclerosis within two years in the intravenous-methylprednisolone group was 0.34 (95 percent confidence interval, 0.16 to 0.74) as compared with the placebo group and 0.38 (95 percent confidence interval, 0.17 to 0.83) as compared with the oral-prednisone group. The beneficial effect of the intravenous-steroid regimen appeared to lessen after the first two years of follow-up. Signal abnormalities on magnetic resonance imaging (MRI) of the brain were a strong indication of risk for the development of definite multiple sclerosis (adjusted rate ratio in patients with three or more lesions, 5.53; 95 percent confidence interval, 2.41 to 12.66). The beneficial effect of treatment was most apparent in patients with abnormal MRI scans at entry. CONCLUSIONS: In patients with acute optic neuritis, treatment with a three-day course of high-dose intravenous methylprednisolone (followed by a short course of prednisone) reduces the rate of development of multiple sclerosis over a two-year period.

Acute Disease↗
PubMed2003

Delayed optic nerve decompression for indirect optic nerve injury.

OBJECTIVE: To test the efficacy of delayed optic nerve decompression in traumatic optic nerve injury. STUDY DESIGN: Critical analysis of Proforma-based, prospectively accrued data of all cases with injury to surgery interval of greater than 2 weeks. METHODS: Thirty-five cases with a median injury to surgery interval of 56 days (range, 16-374 d). Surgical decompression was undertaken only in cases that continued to have poor vision after treatment with steroids in conventional doses (1 mg/kg prednisolone). Pre- and postoperative visual acuity measurements were converted to the logMAR scale of visual acuity and the percentage of visual improvement was calculated. RESULTS: Surgery was universally unrewarding in all 9 cases with persistent and complete blindness of greater than 2 weeks and no response to steroid therapy. Of the cases with some residual vision, 20 of 26 cases improved (mean percentage improvement, 41.0 +/- 5.7%). Cases were categorized on the basis of the injury to surgery interval into groups of 2 weeks to 2 months, 2 months to 4 months, and greater than 4 months. No significant difference was demonstrated in the probability or quantum of improvement in these groups (P =.97). CONCLUSIONS: Optic nerve decompression remains useful as a salvage procedure for conventional dose steroid failed cases of traumatic optic neuropathy. In cases that are not completely blind, vision can be improved even when surgery is undertaken a few months after the injury.

Adolescent↗
PubMed2002

Fractionated stereotactic radiotherapy for the treatment of optic nerve sheath meningiomas: preliminary observations of 33 optic nerves in 30 patients with historical comparison to observation with or without prior surgery.

OBJECTIVE: We investigated the safety and efficacy of stereotactic radiotherapy as an alternative therapy to surgical resection for optic nerve sheath meningiomas (ONSMs). METHODS: Thirty patients and 33 optic nerves with ONSMs were treated with conventional fractionated stereotactic radiotherapy treatment (CF-SRT) between July 1996 and May 2001 with the use of a 6-MeV LINAC designed for and dedicated to radiosurgery. The LINAC technique involved daily CF-SRT involving a relocatable frame, an average of three isocenters, and high-radiation dose conformality established by noncoplanar arc beam shaping and differential beam weighting. The patients who were treated with CF-SRT were followed clinically with serial visual fields and radiographically with both magnetic resonance imaging and functional (111)In-octreotide single-photon emission computed tomography. The results of treatment were compared with a historical control group of ONSM patients who were either observed or treated surgically and then observed. RESULTS: Our study population comprised 18 women and 12 men with a median age of 44 years (age range, 20-76 yr). The median isosurface radiation dose was 51 Gy (dose range, 50-54.0 Gy), and the median clinical follow-up time was 89 weeks (range, 9-284 wk). Of 22 optic nerves with vision before CF-SRT, 20 nerves (92%) demonstrated preserved vision, and 42% manifested improvement in visual acuity and/or visual field at follow-up. Comparison of our patients with a historical control group revealed preserved vision in only 16% of patients in a comparable period of observation, along with a 150% greater probability of visual improvement. Four patients (13%) had posttreatment morbidities, including visual loss (two patients), optic neuritis (one patient), and transient orbital pain (one patient). On magnetic resonance imaging studies, there was no evidence of tumor progression or recurrence in all patients, including tumor volume reductions noted in four patients. All six patients monitored with (111)In-octreotide scintigraphy demonstrated significant decreases in tumor activity after CF-SRT. CONCLUSION: To date, this article describes the largest reported series of ONSMs. Although longer follow-up is necessary, we think that CF-SRT represents a safe alternative to surgery and offers a higher likelihood of preserved or improved vision in patients with ONSM. Our analysis suggests that CF-SRT is also preferable to observation. Functional (111)In-octreotide single-photon emission computed tomographic scintigraphy provides a useful technique for the assessment of tumor control that complements serial posttreatment magnetic resonance imaging in patients with ONSMs.

Adult↗
PubMedDate not supplied

Bulk optical properties and tissue components in the female breast from multiwavelength time-resolved optical mammography.

We present the results of a clinical study about optical properties and bulk composition of the female breast. The clinical study involved more than 150 subjects that underwent optical mammography. A multiwavelength time-resolved mammograph designed to collect time-resolved transmittance images of the breast at different wavelengths in the range 637 to 980 nm is used to this purpose. From the absorption spectrum of the breast, the concentrations of the main tissue constituents, i.e., oxygenated and deoxygenated hemoglobin, lipid, and water, are obtained for a subset of 113 breasts. The lipid content of breast is estimated for the first time on such a large number of subjects. The total hemoglobin concentration, blood oxygen saturation, lipid, and water content of breast is correlated to demographic information collected during the trial. As expected, breast optical properties and components undergo huge variations among different subjects. Different constituents, however, show interesting correlation with clinical parameters such as age, breast size, body mass index, and mammographic parenchymal pattern. These results suggest that optical measurements on breasts can be exploited to obtain relevant information on breast tissue composition.

Breast↗
PubMedDate not supplied

Intraoperatively assessed optical properties of malignant and healthy breast tissue used to determine the optimum wavelength of contrast for optical mammography.

We use spatially resolved diffuse remittance spectroscopy (DRS) for the measurement of absorption (mu(a)) and reduced scattering (mu(s)') coefficients of normal and malignant breast tissue in vivo during surgery. Prior to these measurements, the linearity of the measurement technique was evaluated on liquid optical phantoms. In addition, the reproducibility of in-vivo tissue measurements was determined on a healthy volunteer. We present results of the in-vivo measurement of optical properties in the wavelength range from 600 to 1100 nm performed during radical mastectomy. A total of 24 patients were included in the study. Both the absorption and reduced scattering properties show large variations. Significant differences in optical properties between normal (glandular plus lipid rich tissue) and tumor tissues are present in 74% of all patients. However, in some cases the tumor showed lower values than normal tissue, and in other cases this was the other way around. Thus, a general trend in optical properties is not observed. However, the average absorption contrast of all patients as a function of wavelength reveals an optimal contrast peak at 650 nm. We believe that this relates to a difference in vascular saturation between tumor and adjacent normal tissue.

Breast↗
PubMedDate not supplied

Measurement of optical path length change following pulsed laser irradiation using differential phase optical coherence tomography.

Differential phase optical coherence tomography (DPOCT) is introduced to measure optical path length changes in response to pulsed laser irradiation (585 nm). An analytical equation that includes thermoelastic surface displacement and thermorefractive index change is derived to predict optical path length change in response to pulsed laser irradiation for both "confined surface" and "free surface" model systems. The derived equation is tested by comparing predicted values with data recorded from experiments using two model systems. Thermorefractive index change and the thermal expansion coefficient are deduced from differential phase change (dDeltaphi) and temperature increase (DeltaT0) measurements. The measured n(T0)beta(T0)+dndT[=1.7410(-4)+/-1.710(-6) (1K)] in the free surface experiment matches with the National Institute of Standards and Technology (NIST) data value [=1.7710(-4) (1K)]. Exclusion of lateral thermal expansion in the analytical model for the confined surface experiment causes difference between the measured dndT[=-2.310(-4)+/-7.310(-6)(1K)] and the NIST value [=-9.4510(-5) (1K)]. In spite of the difference in the confined surface experiment, results of our studies indicate DPOCT can detect dynamic optical path length change in response to pulsed laser irradiation with high sensitivity, and applications to tissue diagnostics may be possible.

Body Temperature↗
PubMedDate not supplied

Temperature-dependent optical properties of individual vascular wall components measured by optical coherence tomography.

Optical properties of tissues and tissue components are important parameters in biomedical optics. We report measurements of tissue refractive index n and the attenuation coefficient mu(t) using optical coherence tomography (OCT) of individual vascular wall layers and plaque components. Moreover, since the temperature dependence of optical properties is widely known, we compare measurements at room and body temperatures. A decrease of n and mu(t) is observed in all samples, with the most profound effect on samples with high lipid content. The sample temperature is of influence on the quantitative measurements within OCT images. For extrapolation of ex-vivo experimental results, especially for structures with high lipid content, this effect should be taken into account.

Body Temperature↗
PubMed2001

A comparison of stereoscopic and monoscopic evaluation of optic disc topography using a digital optic disc stereo camera.

AIMS: To compare stereophotographic and monophotographic optic disc assessments made using a digital optic disc stereo camera. METHODS: Stereo digital optic disc photographs of 150 selected patients who had presented to a glaucoma clinic were assessed by two masked observers on separate occasions using (1) the stereophotographs and a stereoviewer, (2) a single image from the same stereopair. Results were analysed for both right and left eyes separately. 95% tolerance limits for change (TC) and intraclass correlation coefficients (ICC) were calculated and a multivariate analysis using a general linear model for repeated measures was performed. RESULTS: A total of 201 optic disc images of 150 patients (84 females, 108 left eyes) were analysed. Mean age of patients was 64 years. The results for right eyes are as follows (similar results were obtained for left eyes). Intraobserver (stereoscopic compared to monoscopic) measurements of: horizontal cup:disc ratios (CDR), ICC = 0.5995 and 0.7269, TC = 34% and 27%; vertical CDR, ICC = 0.8298 and 0.817, TC = 25% and 27%; area CDR, ICC = 0.7757 and 0.8259, TC = 28% and 25%; circumference CDR, ICC = 0.7618 and 0.8103, TC = 28% and 25%. Interobserver measurements of: horizontal CDR, ICC stereoscopic (SS) = 0.7287; monoscopic (MS) = 0.5030; TC SS = 30%; MS = 32%; vertical CDR, ICC SS = 0.8439; MS = 0.7106; TC SS = 25%; MS = 31%; area CDR, ICC SS = 0.8392; MS = 0.6276; TC SS = 26%; MS = 32%; circumference CDR, ICC SS = 0.8433; MS = 0.6438, TC SS = 26%; MS = 31%. Systematic bias between observers and between methods was within acceptable limits. CONCLUSIONS: This study using a digital stereo camera indicates that there may be little benefit of stereoscopic imaging over monoscopic imaging despite demonstrating small but inconsistent differences between both observers and methods.

Adult↗
PubMed2003

Optical biopsy using tissue spectroscopy and optical coherence tomography.

'Optical biopsy' or 'optical diagnostics' is a technique whereby light energy is used to obtain information about the structure and function of tissues without disrupting them. In fluorescence spectroscopy, light energy (usually provided by a laser) is used to excite tissues and the resulting fluorescence provides information about the target tissue. Its major gastrointestinal application has been in the evaluation of colonic polyps, in which it can reliably distinguish malignant from benign lesions. Optical coherence tomography (OCT) has been used in the investigation of Barrett's epithelium (and dysplasia), although a variety of other applications are feasible. For example, OCT could assist in the identification and staging of mucosal and submucosal neoplasms, the grading of inflammation in the stomach and intestine, the diagnosis of biliary tumours and the assessment of villous architecture. OCT differs from endoscopic ultrasound, a complementary modality, in that it has a much higher resolution but lesser depth of penetration. The images correlate with the histopathological appearance of tissues, and the addition of Doppler methods may enable it to evaluate the vascularity of tumours and the amount of blood flow in varices. Refinements in these new optical techniques will likely make them valuable in clinical practice, although their specific roles have yet to be determined.

Animals↗
PubMed1998

The predictive value of CSF oligoclonal banding for MS 5 years after optic neuritis. Optic Neuritis Study Group.

The predictive value of CSF oligoclonal banding for the development of clinically definite MS (CDMS) within 5 years after optic neuritis was assessed in 76 patients enrolled in the Optic Neuritis Treatment Trial. The presence of oligoclonal bands was associated with the development of CDMS (p = 0.02). However, the results suggest that CSF analysis is only useful in the risk assessment of optic neuritis patients when brain MRI is normal and is not of predictive value when brain MRI lesions are present at the time of optic neuritis.

Adolescent↗
PubMed1977

Electrical potentials from the eye and optic nerve of Strombus: effects of electrical stimulation of the optic nerve.

1. Photic stimulation of the mature eye of Strombus can evoke in the optic nerve 'on' activity in numerous small afferent fibres and repetitive 'off' bursts of afferent impulses in a smaller number of larger fibres. 2. Synchronous invasion of the eye by electrically evoked impulses in small optic nerve fibres (apparently the 'on' afferents, antidromically activated) can evoke a burst of impulses in the larger 'off' fibres which propagate away from the eye. Invasion of the eye via one branch of optic nerve can evoke an answering burst in another branch. 3. Such electrically evoked bursts are similar to light-evoked 'off' bursts with respect to their impulse composition, their ability to be inhibited by illumination of the eye, and their susceptibility to MgCl2 anaesthesia. 4. Invasion of the eye by a train of repetitive electrically evoked impulses in the absence of photic stimulation can give rise to repetitive 'off' bursts as well as concomitant oscillatory potentials in the eye which are similar to those normally evoked by cessation of a photic stimulus. 5. The electrically evoked 'off' bursts appear to be caused by an excitatory rebound following the cessation of inhibitory synaptic input from photoreceptors which can be antidromically activated by electrical stimulation of the optic nerve. 6. The experimental results suggest that the rhythmic discharge of the 'off' fibres evoked by the cessation of a photic stimulus is mediated by the abrupt decrease of inhibitory synaptic input from the receptors.

Action Potentials↗
PubMed2003

Precision of measurement of tissue optical properties with optical coherence tomography.

Accurate and noninvasive measurement of tissue optical properties can be used for biomedical diagnostics and monitoring of tissue analytes. Noninvasive measurement of tissue optical properties (total attenuation and scattering coefficients, optical thickness, etc.) can be performed with the optical coherence tomography (OCT) technique. However, speckle noise substantially deteriorates the accuracy of the measurements with this technique. We studied suppression of speckle noise for accurate measurement of backscattering signal and scattering coefficient with the OCT technique. Our results demonstrate that the precision of measurement of backscattering signals with the OCT technique can be 0.2% for homogeneously scattering media and 0.7% for skin, if spatial averaging of speckle noise is applied. This averaging allows us to achieve the precision of tissue scattering coefficient measurements of approximately +/-0.8%. This precision can be further improved by a factor of 2-3, upon optimization of OCT operating parameters.

Animals↗
PubMed2005

Optical slicing of human retinal tissue in vivo with the adaptive optics scanning laser ophthalmoscope.

We present imaging results in human retinal tissue in vivo that allowed us to determine the axial resolution of the adaptive optics scanning laser ophthalmoscope (AOSLO). The instrument is briefly described, and the imaging results from human subjects are compared with (a) the estimated axial resolution values for a diffraction-limited, double-pass instrument and (b) the measured one for a calibrated diffuse retinal model. The comparison showed that the measured axial resolution, as obtained from optical sectioning of human retinas in vivo, can be as low as 71 microm for a 50 microm confocal pinhole after focusing a 3.5 mm beam with a 100 mm focal-length lens. The axial resolution values typically fall between the predictions from numerical models for diffuse and specular reflectors. This suggests that the reflection from the retinal blood vessel combines diffuse and specular components. This conclusion is supported by the almost universal interpretation that the image of a cylindrical blood vessel exhibits a bright reflection along its apex that is considered specular. The enhanced axial resolution achieved through use of adaptive optics leads to an improvement in the volume resolution of almost 2 orders of magnitude when compared with a conventional scanning laser ophthalmoscope and almost a factor of 3 better than commercially available optical coherence tomographic instruments.

Adult↗
PubMed2004

Rapid scanning all-reflective optical delay line for real-time optical coherence tomography.

We describe a dispersion-free high-speed scanning optical delay line that is suitable for real-time optical coherence tomography, in particular, when an ultrabroadband light source is used. The delay line is based on all-reflective optics consisting of two flat and one curved mirrors. We achieve optical path-length scanning by oscillating one of the two flat mirrors with a resonant galvanometer. The delay line is compact and easy to implement. A total scanning depth of 1.50 mm with an 89% duty ratio, a maximal scanning speed of approximately 9.1 m/s, and a 4.1-kHz repetition rate has been demonstrated.

Animals↗
PubMed2004

Extraction of optical scattering parameters and attenuation compensation in optical coherence tomography images of multilayered tissue structures.

A recently developed analytical optical coherence tomography (OCT) model [Thrane et al., J. Opt. Soc. Am. A 17, 484 (2000)] allows the extraction of optical scattering parameters from OCT images, thereby permitting attenuation compensation in those images. By expanding this theoretical model, we have developed a new method for extracting optical scattering parameters from multilayered tissue structures in vivo. To verify this, we used a Monte Carlo (MC) OCT model as a numerical phantom to simulate the OCT signal for heterogeneous multilayered tissue. Excellent agreement between the extracted values of the optical scattering properties of the different layers and the corresponding input reference values of the MC simulation was obtained, which demonstrates the feasibility of the method for in vivo applications. This is to our knowledge the first time such verification has been obtained, and the results hold promise for expanding the functional imaging capabilities of OCT.

Algorithms↗
PubMed1989

[An empirical correlation between optical rotation and absolute configuration of optically active alpha-methylbutyrylphloroglucinols and its synthesis].

Fourteen new compounds were synthesized of which twelve are (S)-(+)-alpha-methylbutyrylphloroglucinols. On the basis of optical rotation data and theoretical analysis, an empirical correlation between optical rotation and absolute configuration of optically active alpha-methylbutyrylphloroglucinols has been established by means of Brewster's rule of atomic asymmetry. It can be served as a means of absolute configuration assignment of optically active alpha-methylbutyrylphloroglucinols.

Molecular Conformation↗