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At least 1,621 records · Page 90Linked to original sources
PubMed1998

Imaging of the optic disc in glaucoma: which way to go?

Less than 10 years ago, fundus photography was believed to be the only method to document optic disc changes in glaucoma. Since then, many sophisticated electronic devices have been developed to supersede conventional photography. At the moment, confocal laser scanning tomography, nerve fiber layer polarimetry, and optical coherence tomography are the most popular techniques. The current status of optic disc imaging in glaucoma can (in our very subjective opinion) be summarized as follows. Confocal laser scanning tomography is the most comprehensively tested electronic modality. It is perhaps the method of choice in major glaucoma centers. Nerve fiber layer polarimetry has forged ahead during the past 2 years and may become an alternative to confocal laser scanning tomography in the future. Optical coherence tomography is a fascinating technique, which may also become important in the future. Right now, however, it is still in the experimental stage. Conventional disc photography--despite all those new techniques--still has its place. Perhaps it is the method of choice in routine glaucoma practice, except those clinics that can afford one of the "high tech" machines.

Diagnostic Imaging↗
PubMed2003

Asymmetric pores in a silicon membrane acting as massively parallel brownian ratchets.

The brownian motion of mesoscopic particles is ubiquitous and usually random. But in systems with periodic asymmetric barriers to movement, directed or 'rectified' motion can arise and may even modulate some biological processes. In man-made devices, brownian ratchets and variants based on optical or quantum effects have been exploited to induce directed motion, and the dependence of the amplitude of motion on particle size has led to the size-dependent separation of biomolecules. Here we demonstrate that the one-dimensional pores of a macroporous silicon membrane, etched to exhibit a periodic asymmetric variation in pore diameter, can act as massively parallel and multiply stacked brownian ratchets that are potentially suitable for large-scale particle separations. We show that applying a periodic pressure profile with a mean value of zero to a basin separated by such a membrane induces a periodic flow of water and suspended particles through the pores, resulting in a net motion of the particles from one side of the membrane to the other without moving the liquid itself. We find that the experimentally observed pressure dependence of the particle transport, including an inversion of the transport direction, agrees with calculations of the transport properties in the type of ratchet devices used here.

Journal Article↗
PubMed2004

Distribution of time-bin entangled qubits over 50 km of optical fiber.

We report experimental distribution of time-bin entangled qubits over 50 km of optical fibers. Using actively stabilized preparation and measurement devices we demonstrate violation of the Clauser-Horne-Shimony-Holt Bell inequality by more than 15 standard deviations without removing the detector noise. In addition we report a proof-of principle experiment of quantum key distribution over 50 km of optical fibers using entangled photon.

Journal Article↗
PubMed2006

Development of a fiber optic enzymatic biosensor for 1,2-dichloroethane.

There is a significant need for devices capable of measuring water contaminant concentrations in situ--continuously, rapidly, and without reagents, extraction, or other pretreatment. Toward this goal, we constructed and tested fiber optic biosensors for measurement of 1,2-dichloroethane (DCA) in aqueous solutions. The biocomponent was the haloalkane dehalogenase, DhlA, in whole cells of Xanthobacter autotrophicus GJ10. These cells were immobilized in calcium alginate on the tip of a fiber optic fluoresceinamine-based pH optode. The resulting biosensor could quantify DCA at 11 mg/l and had a linear response up to at least 65 mg/l. Total signal change was reached in 8-10 min, and measurements were reproducible (SE <9%). The sensor's small size, potential for remote operation, and low cost make it of interest for further development.

Biosensing Techniques↗
PubMed2003

Effect of fluorine plasma treatment on PMMA and their application to passive optical waveguides.

Poly(methylmethacrylate) (PMMA) has been a good prospect for the development of fully amorphous and highly transparent microphotonic devices. The possibilities of a hot embossing technique for the polymeric fabrication of optical waveguides were investigated in this work. A new technique based on radiofrequency plasma treatment was studied for thermal and optical properties, including glass transition temperature, thermal stability, refractive index, and optical transmission loss of PMMA. It is shown that the plasma treatment is effective in altering the functional groups of polymer surfaces without affecting the bulk properties, resulting in effective control of refractive indices and optical transmission losses for photonic applications.

Journal Article↗
PubMed2002

Present state and future perspectives of computer aided surgery in the field of ENT and skull base.

BACKGROUND: CAS technology has emerged in the last 10 years and is more and more used for surgery of the anterior and lateral skull base. Endoscopic and microscopic CAS systems are available. The endoscopic key hole or minimal invasive procedure is used increasingly not only for treatment of inflammatory disease, but also for tumour surgery. The integration of CAS systems into these procedures raises the level of their safety and efficiency. In addition, they allow the distance to the bone border on the CT slices to be previewed and measured. OBJECTIVE: Review of the present state of CAS systems, our own experience as a research centre and as users of the systems, demonstration of new navigational devices, microscope integration and a new registration procedure developed for the "Bernese" frameless optical navigation system (SurgiGATE ORL@1000, medivision, [Synthes, Stratec-medical], CH-4436 Oberdorf). MATERIAL AND METHODS: The optical CAS system with microscope integration (VM 900@1000, Möller-Wedel, Germany), new devices and new matching procedure; accuracy tests on a cadaver skull and on the patient's head. RESULTS: The practical accuracy on the cadaver skull with the pointer system has a mean average error of 0.79 mm, and the clinical accuracy is between 0.5 mm and 2 mm. CONCLUSION: CAS-microscope integration, new CAS technical devices and new noninvasive CAS-registration procedures support the surgeon in more minimally invasive surgical procedures of the paranasal sinuses and the skull base. Future perspectives will be discussed.

Humans↗
PubMed2006

Importance of scattering and absorption for the outcoupling efficiency in organic light-emitting devices.

The outcoupling of light in organic light-emitting devices is one of the limiting parameters for obtaining a high external efficiency. A simple geometrical model is presented that allows one to estimate the importance of optical parameters such as mirror reflectivity, scattering probability, and device structure. The model allows the derivation of analytical expressions for the outcoupling efficiency in some simplified cases.

Journal Article↗
PubMed2002

Low-temperature-GaAs device used simultaneously as a mode-locking device and as a photoconductive switch.

We present a low-temperature-grown GaAs device that combines the features of mode locking and photoconductive switching. The mode-locking mechanism is based on intensity-dependent defocusing. Additionally, the generated carriers produce an electrical signal in the biased switch geometry. This technique allows for simultaneous generation of synchronized optical and electrical pulse trains with a single device.

Journal Article↗
PubMed2005

Bandwidth control in a hybrid fiber acousto-optic filter.

We report a bandwidth variation technique in an acousto-optic filter. Utilizing the adiabatic conversion in both optical and acoustic modes, we obtain a novel hybrid waveguide composed of serial concatenation of single-mode fiber (SMF) and two-mode hollow optical fiber (HOF). On the basis of dissimilarity in the phase-matching conditions and beat-length dispersion in SMF and HOF, the FWHM of the resonant bands is varied from 3.8 to 190 nm near the 1.5-microm region in a single device. Furthermore, we theoretically analyze the acousto-optic coupling among the guided modes in HOF, which shows good agreement with experimental observations.

Journal Article↗
PubMed2002

Quantification of histological changes after calibrated crush of the intraorbital optic nerve in rats.

BACKGROUND: Traumatic optic nerve lesions (TONL) are probable but unpredictable consequence after severe midface or skull base trauma. Based on a previously described rat model, the authors developed a new model in order to simulate optic nerve crush during trauma on the optic canal. METHODS: To achieve a calibrated TONL, a microinjuring device was designed that made it possible to assess the correlation between a defined trauma and the neuronal degeneration in the rat retinal ganglion cell (RGC) layer. This device is based on a small dynamometer mounted onto a conventional micromanipulator. The supraorbital approach was chosen to expose the extracranial optic nerve. RESULTS: In this rat model (n=100, Wistar strain) the parameters of "force" and "time" could be precisely monitored during the experiment. The decrease in the mean number of retinal neurons (N) according to the pressure exerted (2-30 cN x mm(-2)) on the optic nerve was linear for 1, 6, and 15 minutes of injuring time; the decrease in N for varying injuring forces also appears to be nearly linear. CONCLUSION: The results show that this model provides a reliable method for studying quantitatively the anatomical effects of TONL on the RGC layer and the optic nerve itself, and may allow the design of treatment strategies following TONL.

Animals↗
PubMed1999

Comparison of 24-2 and 30-2 perimetry in glaucomatous and nonglaucomatous optic neuropathies.

OBJECTIVE: To determine whether the 24-2 Humphrey visual field (HVF) (Humphrey, San Leandro, CA) strategy provides information comparable to that provided by the 30-2 strategy in patients with optic nerve disease. METHODS: In part A of the study, an occluder device was designed to cover the additional outer 22 points tested in the 30-2 strategy of 187 HVFs from neuro-ophthalmology patients with nonglaucomatous optic neuropathy and 206 HVFs from patients with glaucoma. This device converted the gray scale and probability plots of the 30-2 HVF to a 24-2 field. Fields were initially read using the occluder and then were read in a masked manner without the occluder and compared. In part B, 15 healthy volunteers performed both 30-2 and 24-2 HVFs. Testing time and global indices were compared. Ninety-five percent of the fields in the neuro-ophthalmology patients, 96% of the fields in patients under observation for suspected glaucoma, 98% of the fields in patients with ocular hypertension, and 100% of the fields in patients with glaucoma were read similarly with the 24-2 and 30-2 strategies. In the few cases in which a discrepancy was noted between the 24-2 and the 30-2 fields, appropriate clinical management would not have been compromised by using the 24-2 strategy. Most of these cases were in patients with idiopathic intracranial hypertension and very subtle nerve fiber bundle defects. The 24-2 strategy had a significantly lower pattern standard deviation (P < 0.01) and corrected pattern standard deviation (P = 0.05) than did the 30-2 strategy. In addition, the 24-2 strategy shortened the standard threshold testing time by 28% in normal volunteers (P < 0.0001 ). CONCLUSIONS: In most cases, the 24-2 testing strategy provides information comparable to that provided by the 30-2 strategy in a shorter time and with less variability. A 30-2 HVF may be warranted in patients under observation for evolving idiopathic intracranial hypertension.

Glaucoma↗
PubMed2005

An integrated metal clad leaky waveguide sensor for detection of bacteria.

An integrated optical metal clad leaky waveguide (MCLW) sensor device has been developed for the detection of bacteria. This is more sensitive than waveguide sensors currently in use. The MCLW device has been fabricated to extend the evanescent field to provide significant light intensity over the entire volume of the bacteria bound on the chip surface within this field. This in turn increases the interaction of the light with the entire volume of the bacteria. MCLW devices have been used for detecting refractive index changes, scattering, and fluorescence from bacterial spores captured on an immobilized antibody. The detection limit of Bacillus subtilis var. niger bacterial spores using refractive index detection was 8 x10(4) spores/mL. The scattering intensity of the BG spores was found to be three times greater than the scattering intensity generated using surface plasmon resonance. The extended light propagation along the direction of flow for a few millimeters provides an effective interrogation approach to increase the area of detection to detect low concentrations down to 1 x 10(4) spores/mL. The sensor was then optimized by studying the key factors affecting sensor performance including changing the pH of the medium, type of antibody immobilization matrix, sensor surface regeneration approaches, and longevity of the sensor.

Bacteria↗
PubMed1990

Thermal characteristics of sapphire contact probe delivery systems for laser angioplasty.

Contact probes made from synthetic sapphire crystal, designed for general laser surgery, are currently being evaluated for use in laser angioplasty. Their mode of action and safety in the context of arterial recanalisation is unknown, particularly with respect to the degree of probe and catheter heating. Infrared thermal imaging was used to investigate the surface temperature rise of various rounded sapphire probes during emission of continuous wave Nd-YAG (1,064 nm) laser energy. Catheter safety was addressed by analyzing the temperature of the metal interface between the optical fiber and sapphire, as well as the catheter proximal to this junction. Transmission of Nd-YAG energy through each probe was also measured. Five rounded probes of 1.8-3.0 mm diameter (three supplied by Surgical Laser Technologies [SLT], two by Living Technology [LT]), along with their respective optical catheters, were compared. There was a large temperature gradient between the front and rim of the probes. The maximum surface temperature rise of the sapphire (at 20 W, 5-second exposure) was 314-339 degrees C (SLT) and 90-108 degrees C (LT) [P less than 0.001, 3-way ANOVA]. The reason for this difference may be related to "crazing" of the front surface of the SLT sapphires. At all energy levels sapphire temperatures were considerably lower than attained by metal laser thermal angioplasty probes. Forward transmission was slightly higher in the SLT probes (75-85%) than the LT sapphires (54-69%). With fiber perfusion at 2 ml/minute, a minor degree of heating of the metal sapphire holders was recorded (maximum rise 35 degrees C), but heating of the catheter proximal to this was negligible. Therefore, it would appear that the risk of tip detachment or arterial injury due to heating of the connecting metal interface is extremely low. Without perfusion, however, there was a greater degree of interface heating in the LT delivery system suggestive of more laser backscattering by these sapphires compared with the SLT probes [P less than 0.001, one-way ANOVA]. The SLT system is, therefore, potentially safer in this respect. These results suggest that some degree of surface heating of contact probes due to energy absorption within the sapphire does occur, but is localised to the front of the probe. This effect may contribute to the process of arterial recanalisation with this device. However, variation in the thermal and optical properties of sapphires from different sources has been demonstrated. The influence of these properties on plaque ablation, and ultimately the clinical performance of different contact probe systems, requires further investigation.

Humans↗
PubMed2001

Use of the optical access trocar for safe and rapid entry in various laparoscopic procedures.

BACKGROUND: The use of the Veress needle in laparoscopy to create the pneumoperitoneum has inherent risks; it may cause vascular and visceral injuries. The open technique is compromised by the leakage of carbon dioxide and can also be time consuming. One alternative is to enter the abdomen using an optical trocar under direct view. Our aim was to determine whether the optical access trocar can be used to effect a safe and rapid entry in various laparoscopic procedures. METHODS: Over a 4-year period, the Optiview trocar was used for initial entry in 650 laparoscopic procedures. The procedures included cholecystectomy (n = 282), transabdominal inguinal hernia repair (n = 76), radiofrequency ablation of liver tumors (n = 73), adrenalectomy (n = 54), appendectomy (n = 41), colorectal surgery (n = 39), and various other procedures (n = 85). The following parameters were analyzed: presence of previous abdominal operations, site and duration of entry, and complications. RESULTS: Of the 650 patients, 156 (24%) had had previous abdominal operations. In 25 cases, previous trocar sites were reused for optical access. The optical trocar was inserted at the umbilicus in 495 patients (76%), in the right upper quadrant in 77 (12%), in the left upper quadrant in 26 (4%), in the upper midline in eight (1%), in the right lower quadrant in six (0.9%), and in the left lower quadrant in three (0.5%). In 35 patients undergoing posterior adrenalectomy, optical trocars were used to enter Gerota's space. Mean (SD) entry times were 92 (45) sec at the umbilical site, 114 (30) sec at the back, and 77 (35) sec at the remaining sites. Complications (0.3%) included one injury to the bowel and one injury to the gallbladder; however, they were recognized and repaired immediately. CONCLUSIONS: To our knowledge, this report comprises the largest series in which the optical access trocar was used for laparoscopic surgery. This device provides the basis for a safe and fast technique for initial trocar placement: it also has the potential to reduce costs. Thanks to our favorable experience, the optical trocar method has become the standard technique for abdominal access in our laparoscopic practice since 1995.

Abdomen↗
PubMedDate not supplied

Miniaturized thermal lens device for capillary electrophoresis.

In this paper we will report on the combination of a miniaturized fiber optic modified photothermal sensor (size 2 x 2 x 2 cm) to capillary electrophoresis (CE) as detection device. The properties and the performances of the thermal lens detector, based on a double beam absorption scheme, were studied in a capillary electrophoresis system with different types of toxic pollutants, e.g. pesticides. A tunable Argon ion laser, which emits between 364 and 514 nm, was adapted to a commercial injection and high voltage CE system. The miniaturization of the thermal lens detector head with optical waveguides allows the combination with typical CE systems, therefore pesticides in microliter volumes can be treated. The detector performance is demonstrated with the monitoring of pesticides in capillaries with various diameter. The limit of detection is one of two orders of magnitude better than conventional absorption detector.

Electrophoresis, Capillary↗
PubMed2006

Legeais BioKpro III keratoprosthesis implantation: long term results in seven patients.

AIMS: The long term results of the Legeais BioKpro III keratoprosthesis are presented for seven patients with severe corneal scarring. METHODS: The study took place at Moorfields Eye Hospital, London. Patients had either end stage ocular surface disease or corneal opacification after multiple failed graft surgery, with the potential for significant visual improvement. After insertion the device was covered with a conjunctival flap or buccal mucous membrane graft, which was later opened to expose the optic. The outcome measures were vision, complications, and retention of the device. RESULTS: The BioKpro III was inserted into seven patients with severe corneal scarring: ocular cicatricial pemphigoid, measles keratitis, thermal injury, Stevens-Johnson syndrome, aniridia, chemical injury, and congenital rubella. The follow up was 18-48 months. The keratoprosthesis failed in six, because of extrusion occurring 2-28 months postoperatively. Retroprosthetic membranes occurred in three patients, and endophthalmitis in one. Vision improved from hand movements to 6/12 in the only patient who retained the KPro; however he was troubled by mucus accumulation on the optic. CONCLUSIONS: The one success has been in a patient with thermal burns. The remaining results have been poor, with the KPro extruding in six of the seven patients.

Adult↗
PubMed1997

A new fibre optic sensor for respiratory monitoring.

A new fibre optic plethysmograph has been designed to monitor respiration non invasively. The device incorporates the idea of using thoracic and abdominal belts similar to conventional inductance plethysmography but uses an optical fibre woven into the belts rather than the usual coiled wire. The fibre optic belts incorporate a loop design in the fibre and rely on "macrobending" losses from laser light transmitted down the fibre when the bend radius of the loop changes during respiration. Changes in lung volume are monitored by analysing the relatively large resultant changes in light transmitted through the fibre. The output from the light detector has been interfaced to a computer containing a data acquisition card and the resultant intensity trace is monitored in real time using a virtual instrument created using LabVIEW graphical programming. Preliminary results suggest a highly sensitive system capable of detecting small changes in lung volume using a technique which is not susceptible to electrical noise and which is electrically safe.

Adult↗