Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “OPTICS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16Linked to original sources
PubMed1977

Review of diseases of the optic nerve, optic tract, and visual cortex: 1975-76.

The ophthalmic literature dealing with diseases of the optic nerve, the optic tracts, and the visual cortex was reviewed for the period November 1975 through November 1976. Twenty-nine papers on topics of interest to optometrists were abstracted. The main areas of interest include: papilledema and optic atrophy (with ophthalmoscopic signs of both optic atrophy and papilledema); giant-cell arteritis; papillitis; interesting malformations of the face, palate, and orbital position that occur in conjunction with microphthalmus, situs inversus, and hypoplasia and aplasia of the optic nerve; the proposed association of myopia with unusual eyebrows; myelinated nerve fibers at the nerve head; pigment anomalies; the continuing discussion of nerve-head blood supply; an unexpected cause for nerve-head neovascularization; the importance of the swinging-flashlight test in the diagnosis of glaucoma; an unusual type of glaucomatous cupping; doubts about the peripapillary "halo" as a sign of glaucoma; new uses for old field tests; and new methods of ocular photography.

Abnormalities, Multiple↗
PubMed1994

Optic disc cupping in arteritic anterior ischemic optic neuropathy.

Patients with anterior ischemic optic neuropathy due to giant cell arteritis are thought to develop optic disc cupping, resembling that seen in glaucomatous eyes, while such cupping does not seem to occur in nonarteritic anterior ischemic optic neuropathy. However, this remains controversial. We describe a patient with arteritic anterior ischemic optic neuropathy (the clinical diagnosis was confirmed with a biopsy from the temporal artery) who developed disc cupping within 4 months after acute episode. This patient never had elevated intraocular pressure, and prior to the acute event the optic nerve heads had had a normal appearance with a physiologic cup.

Aged↗
PubMed2006

[Reproducibility of optic nerve head and retinal nerve fiber layer thickness measurements using optical coherence tomography].

PURPOSE: To evaluate the reproducibility of repeated quantitative measurements of optic nerve head topography and retinal nerve fiber layer thickness. METHODS: This study included 32 normal subjects, 41 patients with ocular hypertension and 33 patients with glaucoma. The study groups were defined by the intraocular pressure levels, optic disc stereo-photographs and perimetric performance. Optic disc and retinal nerve fiber layer assessments were performed by ocular coherence tomography (OCT III, Zeiss Instruments). OCT examination was repeated three times in each subject and the coefficient of variability was elaborated for each parameter and group of the study, and compared among them. RESULTS: The average retinal nerve fiber layer thickness measurement showed the best reproducibility figures with a coefficient of variability of 5.9%. The inferior quadrant and the 10, 6 and 7 clock-hours (coefficients of variability 6.3%, 7.4%, 7.5% and 8.6% respectively) showed higher reproducibility. The optic nerve head assessment showed the best reproducibility for the cup-to-disc ratios (vertical, horizontal and area ratios), with a coefficient of variability of 5.0%, 4.2% and 6.6% respectively. Although differences among groups were barely statistically significant, the glaucoma group showed coefficients of variability higher than the other two groups. CONCLUSIONS: Optic nerve head analysis and retinal nerve fiber layer thickness can be reproducibly assessed by OCT. The reproducibility of the device supports its potential use for ocular hypertension follow-up, although its use in glaucoma patients may present difficulties in some parameters.

Female↗
PubMed1994

Directed movement of chromosome arms and fragments in mitotic newt lung cells using optical scissors and optical tweezers.

A pulsed-laser microbeam at 532 nm wavelength (optical scissors) and a laser-induced optical trap at 1064 nm wavelength (optical tweezers) have been successively combined to dissect and manipulate chromosomes in live newt lung epithelial cells. These preliminary experimental results demonstrated that chromosome fragments dissected by laser microbeam surgery, regardless of their size, could be easily pulled or rotated by optical forces when positioned at the periphery of the mitotic spindle. In addition, chromosome arms which were not subjected to laser microsurgery also could be moved with the optical tweezers at the spindle periphery. In our previous study on rat kangaroo kidney cells (PTK2), this degree of facilty in manipulating chromosome movement was not possible, most likely due to the close proximity of the intermediate filament "cage" to the spindle. It is concluded herein that optical scissors and tweezers can be used in combination to study the interaction of chromosomes with the mitotic spindle in cells where the peripheral regions of the spindle are unobstructed by intermediate filaments. This can be performed on newt cells, where the diameter of the cage can be substantially larger than the diameter of the spindle.

Animals↗
PubMed2002

Hydrophobic optical elements for near-field optical analysis (NOA) in liquid environment--a preliminary study.

Near-field Scanning Optical Microscopy (NSOM) in liquid environment is expected to allow time resolved morphological mappings on cellular surfaces on the nanoscale level. Near-field Optical Analysis (NOA) via NSOM exploits the energy transfer from the tip of an optical element (tip diameter > or = 20nm), oscillating within the range of the characteristic length of the energy transfer ( approximately 10nm) in the near-field of the surface to be analysed. In NOA, a molecular assembly is monitored by visible light with a resolution far below the wavelength of visible light. Actually, NOA is successfully applied in mapping local optical contrasts, for instance in photonic crystals with dielectric periodicities on the nanoscale. NSOM could in principle be performed in two different modes: tapping mode, with tip-oscillations perpendicular, or shear force mode, with tip-oscillations parallel to the substrate. Both basic modes have specific advantages and disadvantages. In biological systems (e.g. in cell cultures), where scanning in liquids is prevalent, elongated optical elements non-invasively operated in the shear force modus could have some specific advantages when compared to contact modus systems. While tapping mode NSOM provides satisfactory nanoscale images even on solid surfaces covered with millimetres of liquids, the performance of shear force mode NSOM is presently largely confined to operations on dry samples. This is due to the inability of conventional shear force mode NSOM systems to provide sharp topographic images of sample surfaces substantially covered with liquids. By equipping a conventional NSOM system with hydrophobic optical elements, shear force mode based topographic images could be obtained on biological samples in dry as well as in aqueous environment, and with resolutions on the nanoscale level.

Journal Article↗
PubMedDate not supplied

Brighter near-field optical probes by means of improving the optical destruction threshold.

The optical destruction thresholds of conventionally etched and tube-etched near-field optical probes were measured. One of the main advantages of tube-etched tips is their smooth glass surface after taper formation. Presumably for this reason, a destruction limit of over 120 microJ was obtained, almost twice as large as that of the rougher, conventionally etched fibre probes. The use of additional adhesion layers (Ti. Cr, Co and Ni) between the glass surface and the aluminium coating produced, especially for tube-etched tips, a significant increase in the optical destruction threshold. With increasingly thin metal coatings, the use of a protection coating that prevents corrosion during aging is recommended. An additional increase in optical stability was achieved by applying mixed-metal coatings: alternating thin titanium and thick aluminium layers yielded fibre probes with superior properties that achieved average optical destruction thresholds of > 270 microJ. This is an increase in stability of > 400% compared with conventionally fabricated near-field optical tips.

Journal Article↗
PubMed2001

Photothermal determination of optical coefficients of tissue phantoms using an optical fibre probe.

The absorption and reduced scattering coefficients of turbid tissue phantoms have been determined from photothermal measurements made using an optical fibre probe. The thermal sensor was a thin polymer film positioned at the end of a multimode optical fibre. The film was illuminated by the output of a continuous-wave diode laser and formed the cavity of a low-finesse Fabry-Perot interferometer. Low energy laser pulses, launched into the fibre and passed through the film, produced an abrupt temperature rise in the target tissue, which was placed in contact with the film. The subsequent conduction of heat into the film caused a change in its optical thickness and hence the reflected intensity. The absorption and reduced scattering coefficients of gelatine tissue phantoms of known optical properties were determined from the measurements using a numerical model of photothermal signal generation and maximum a posteriori estimation. The determined optical coefficients were in good agreement with the known values. The results showed that the probe can be used for the determination of optical coefficients provided the thermal coefficients of the target tissue are known with low uncertainty.

Gelatin↗
PubMed2006

Effect of optical property estimation accuracy on tomographic bioluminescence imaging: simulation of a combined optical-PET (OPET) system.

Inevitable discrepancies between the mouse tissue optical properties assumed by an experimenter and the actual physiological values may affect the tomographic localization of bioluminescent sources. In a previous work, the simplifying assumption of optically homogeneous tissues led to inaccurate localization of deep sources. Improved results may be obtained if a mouse anatomical map is provided by a high-resolution imaging modality and optical properties are assigned to segmented tissues. In this work, the feasibility of this approach was explored by simulating the effect of different magnitude optical property errors on the image formation process of a combined optical-PET system. Some comparisons were made with corresponding simulations using higher spatial resolution data that are typically attainable by CCD cameras. In addition, simulation results provided insights on some of the experimental conditions that could lead to poor localization of bioluminescent sources. They also provided a rough guide on how accurately tissue optical properties need to be known in order to achieve correct localization of point sources with increasing tissue depth under low background noise conditions.

Animals↗
PubMed2003

Circularly polarized optical heterodyne interferometer for optical activity measurement of a quartz crystal.

Phase retardation between two orthogonal circularly polarized light waves that propagate in an optical active medium is proportional to its optical activity. The measurement of optical activity of a quartz depolarizer in terms of the phase difference of two orthogonal circularly polarized waves is proposed. A circularly polarized optical heterodyne interferometer with a Zeeman laser to measure the optical activity of a quartz crystal is demonstrated experimentally. The accuracy of the measurement is discussed. In addition, the effect of elliptical polarization and nonorthogonality of linearly polarized light waves of a Zeeman laser on the optical activity measurement is analyzed.

Journal Article↗
PubMed2004

Telecentric confocal optics for aberration correction of acousto-optic tunable filters.

A telecentric confocal optical arrangement is presented that greatly reduces the diffraction aberrations of the acousto-optic tunable filter (AOTF). Analytical expressions for the aberrations were identified based on the fundamental properties of Bragg diffraction, and additional aberrations due to focusing through the AOTF were also included. The analysis was verified by use of a geometrical ray trace optical code, and an experimental AOTF system was analyzed. Considerable improvement in the potential spatial resolution is predicted with confocal optics, which could accommodate large pixel-limited image fields of greater than 10(6) pixels. When the image quality of the experimental system was assessed, the resolution was found to be improved by the confocal optics and was diffraction limited. Higher resolution could have been obtained with the use of larger optics to increase the throughput before being limited by the aberrations.

Journal Article↗
PubMed2005

Axial optical trapping forces on two particles trapped simultaneously by optical tweezers.

Optical tweezers, which utilize radiation pressure to control and manipulate microscopic particles, are used for a large number of applications in biology and colloid science. In most applications a single optical tweezers is used to control one single particle. However, two or more particles can be trapped simultaneously. Although this characteristic has been used in applications, no theoretical analysis of the trapping force or the status of the trapped particles is available to our knowledge. We present our calculation, using a ray optics model, of the axial trapping forces on two rigid particles trapped in optical tweezers. The spherical aberration that results from a mismatch of the refractive indices of oil and water is also considered. The results show that the forces exerted by the optical tweezers on the two particles will cause the two particles to touch each other, and the two particles can be stably trapped at a joint equilibrium point. We also discuss the stability of axial trapping. The calculation will be useful in applications of optical tweezers to trap multiple particles.

Journal Article↗
PubMed2005

Use of null optics for monitoring the optical alignment of a beam director.

The use of null optics is proposed as a new concept for monitoring the optical alignment of a beam director. Null optics consist of a primary mirror and an annular mirror just outside the aperture of the secondary mirror. The characteristics of the proposed null optics are investigated with the designed sample of a two-mirror system with an effective aperture of 275 mm. The results show that null optics yield four times the amplification with respect to the alignment errors of the secondary mirror; however, they have low residual aberration sensitivity to misalignment. Therefore null optics can be used successfully as the alignment monitoring apparatus of a beam director.

Journal Article↗
PubMed2005

Concurrent generation of an optical code label and payload data by use of phase and intensity modulators for all-optical packet switching.

We propose and experimentally demonstrate the concurrent generation of an optical code label and payload data by use of off-the-shelf optical intensity and phase modulators in a tandem structure. This technique is capable of reconfigurable generation of an arbitrarily long optical code label of phase-shift keying concurrently with the generation of payload data, without the need for a special class of optical encoder. This technique will be powerful for all-optical packet switching networks, based on scalability and compactness, for optical code labels.

Journal Article↗
PubMed1999

Optic flow input to the hippocampal formation from the accessory optic system.

Recent studies in rodents have implicated the hippocampal formation in "path integration": the ability to use self-motion cues (ideothesis) to guide spatial behavior. Such models of hippocampal function assume that self-motion information arises from the vestibular system. In the present study we used the retrograde tracer cholera toxin subunit B, the anterograde tracer biotinylated dextran amine, and standard extracellular recording techniques to investigate whether the hippocampal formation [which consists of the hippocampus proper and the area parahippocampalis (Hp/APH) in pigeons] receives information from the accessory optic system (AOS). The AOS is a visual pathway dedicated to the analysis of the "optic flow fields" that result from self-motion. Optic flow constitutes a rich source of ideothetic information that could be used for navigation. Both the nucleus of the basal optic root (nBOR) and nucleus lentiformis mesencephali of the AOS were shown to project to the area ventralis of Tsai (AVT), which in turn was shown to project to the Hp/APH. A smaller direct projection from the nBOR pars dorsalis to the hippocampus was also revealed. During extracellular recording experiments, about half of the cells within the AVT responded to optic flow stimuli. Together these results illustrate that the Hp/APH receives information about self-motion from the AOS. We postulate that this optic flow information is used for path integration. A review of the current literature suggests that an analogous neuronal circuit exists in mammals, but it has simply been overlooked.

Animals↗
PubMed2000

Pattern of vascular nonperfusion in retinal venous occlusions occurring within the optic nerve with and without optic nerve head swelling.

OBJECTIVE: To investigate the significance of optic nerve head swelling (ONHS) in relation to the pattern of vascular nonperfusion, visual acuity (VA), and demographic profile in retinal venous occlusions (RVOs) occurring within the optic nerve. METHODS: Cases of RVO occurring within the optic nerve were divided on the basis of the presence (105 cases) or absence (163 cases) of ONHS. This division was performed by examining the color stereo fundus photographs in conditions masked from other clinical parameters. Duration of symptoms before assessment, age, and sex distributions were compared. The vein involved was identified, and the occlusion was confirmed to have occurred within the optic nerve by observing that the vein pierced the lamina cribrosa as a dilated vein. Fluorescein angiographs were examined, and the extent of vascular nonperfusion in the macula and peripheral retina was quantified from grade 1 to grade 4. The extent of break in the perifoveal capillary arcade was graded as 0, less than or equal to 90 degrees, and greater than 90 degrees. Best-corrected VA was assessed using the Snellen chart. RESULTS: The 2 groups were comparable in terms of the duration of the symptoms before examination. The mean age was significantly younger in the group with ONHS (58.3 vs 65.1 years, P<. 001). Age distribution by sex demonstrated a higher proportion of men younger than 50 years in the ONHS group (19.1% vs 8.6%, P =.01). The group without ONHS involved the papillary vein more frequently (31.3% vs 17.1%, P =.01). The respective proportions of grade 1, 2, 3, and 4 vascular nonperfusion in the macula were 90.5%, 9.5%, 0%, and 0% in the ONHS group, and 62.6%, 14.7%, 13.5%, and 9.2% in the group without ONHS (P<.001). The corresponding proportions for the peripheral retina were 90.4%, 8.7%, 0%, and 1.0% in the ONHS group, and 62.7%, 13.0%, 18.0%, and 6.2% in the group without ONHS (P<.001). In 64.6% of cases with ONHS and 42.9% of cases without, the perifoveal arcade was intact. A break greater than 90 degrees in the perifoveal arcade was present in 12.5% of cases with and 23.6% of cases without ONHS (P =.004). The median VA was significantly better in the ONHS group (6/24 vs 6/48, P =.005). CONCLUSIONS: The RVOs occurring within the optic nerve can be subdivided into 2 distinct groups on the basis of ONHS. The presence of ONHS is associated with younger age, less severe vascular nonperfusion, and better VA. This is consistent with a retrocribrosal site of occlusion, which has access to the pial plexus that can provide collateral channels for retinal venous drainage.

Adult↗
PubMed1993

Optic nerve sheath decompression for glaucomatous optic neuropathy with normal intraocular pressure.

OBJECTIVE: To report our therapeutic experience with optic nerve sheath decompression in patients with normal-pressure glaucoma. DESIGN: A case series of seven eyes from six patients with glaucoma and normal intraocular pressures who continued to have progressive visual field loss despite conventional therapy. SETTING: A hospital-based, referral glaucoma service. PATIENTS: Three men (67, 67, and 72 years of age) and three women (58, 61, and 70 years of age). INTERVENTIONS: Optic nerve sheath decompression. MAIN OUTCOME MEASURES: Visual field data and visual acuity measurements were obtained at regular intervals during the postoperative periods (range, 3 to 18 months). RESULTS: Two of seven eyes from six patients appear to have enjoyed an initial significant improvement in their visual fields with improved visual acuity in one eye of one patient. The visual fields, however, appear to have deteriorated 18 months after the initial procedure in these two patients. In the remaining four patients, no further improvement or deterioration was observed within a limited follow-up period. CONCLUSIONS: The transient improvement in the visual fields of one eye from each of two patients documents an initial successful use of optic nerve sheath decompression in patients with nerve fiber bundle damage in the absence of optic nerve head swelling. However, the long-term potential of optic nerve sheath decompression in these patients may be of limited value.

Aged↗
PubMed2006

Quantifying axonal loss after optic neuritis with optical coherence tomography.

OBJECTIVE: To determine to what degree changes in retinal nerve fiber layer (RNFL) thickness after optic neuritis (ON) correlate with either visual recovery or impairment. METHODS: ON can cause visible defects within the RNFL, which can be quantified using optical coherence tomography (OCT). It may be possible to predict visual recovery by measuring RNFL loss after ON. Fifty-four patients underwent repeated evaluations with optical coherence tomography and standardized ophthalmic testing after ON. Regression analyses were used to determine the relationship between RNFL thickness and visual function. RESULTS: Thinning of the RNFL was seen in the majority of patients (74%), and it tended to occur within 3 to 6 months of ON. The average RNFL value was thinner (p<0.0001) in the affected (78 microm) compared with the unaffected eye (100 microm). Patients with incomplete visual recovery demonstrated greater RNFL loss after ON. Regression analyses demonstrated a threshold of RNFL thickness (75 microm), below which RNFL measurements predicted persistent visual dysfunction. INTERPRETATION: Determination of RNFL thickness may predict visual recovery after ON, and lower RNFL values correlate with impaired visual function. Optical coherence tomography may have a potential role as a surrogate marker for axonal integrity within the optic nerve among patients with ON.

Adolescent↗