Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Telescopes”

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 109 records · Page 6Linked to original sources
PubMed1977

Telescopes, light vergence, and accommodation.

This paper explains why the accommodative response to near objects is ineffective through a telescope. A simple formula is used to demonstrate the need for a bifocal spectacle objective or a change in vertex distance when viewing near objects with a contact lens spectacle lens telescope. Using this exact formula, clinicians can now more precisely compare refractions with and withoug a telescope. The formula also shows why refractions with telescopes used for driving should be accomplished at test distances of 20 feet or more.

Accommodation, Ocular↗
PubMed1979

Variation of image vergence with change in object distance for telescopes: the general case.

Three formulas are given and derived which can be used to evaluate the relationship between image vergence and object position for any two-lens system and will be very useful in the special case of telescopes. A corresponding formula for afocal telescopes has been published previously. The formulas presented here are applicable to all non-afocal (focal) telescopes, including particular types such as near point telescopes. All that is required for their evaluation is the positions of one pair of conjugate planes, the corresponding magnification, and the lens separation. The formulas can be used to estimate such quantities as a working or useful depth of field and accommodation demand, particularly when the optical system is not used at its design conjugates. A numerical example is presented.

Accommodation, Ocular↗
PubMed1980

Working distance comparison of plus lenses and reading telescopes.

Low vision aids used in the spectacle plane may be either plus lenses or telescopes focused for near. The plus lens has a shorter working distance than a near point telescope of the same equivalent power. A relationship between the anterior focal length (fv) of the near point telescope and the equivalent focal length (fe) of a thin lens of equal power can be derived from the formula fv = (mag) (fe). This formula provides a basis for determining what equivalent powers are equal and interchangeable between the two types of aids. Furthermore, the advantages of the increased working distance afforded by the near point telescope can be defined.

Eyeglasses↗
PubMed1992

Challenges in applying autofocus technology to low vision telescopes.

Autofocus (AF) low vision telescopes offer the potential to increase the acceptance and utilization of such low vision aids (LVA) by the visually impaired. Many patients resist conventional manual focus telescopes for a variety of reasons including appearance, field of view, weight, and utility. The elderly who comprise the significant part of the target population may also resist telescopes due to an avoidance of the technical challenge of its use. Although an AF telescope is technically advanced, it may allow for less manipulation by the wearer and hence enable its more effective application to visual tasks, especially in the near- to mid-range where depths of field narrow and the demands for focusing increase. There are many challenges involved in the application of AF technology to LVA including modification of the focusing range, signal processing for physiologically acceptable performance, and power and weight considerations. A preliminary infrared (IR) AF prototype based upon our recent work with the Ocutech Vision Enhancing System (VES) has been produced. Initial findings are presented which address the requirements of a subsequent version as well as the challenges that will be faced to optimize such a device.

Audiovisual Aids↗
PubMed1995

Field of view and equivalent viewing power of near-vision telescopes.

There are often substantial differences in linear field of view (FOV) and equivalent viewing power (EVP) when a distance telescope is either fitted with an objective lens cap or adjusted in length to focus for near vision. In addition, larger differences in linear FOV are found for Galilean than for Keplerian telescopes of similar magnification and EVP. Simple formulas are presented here that make use of EVP as a factor for calculating the linear FOV ratio between the two methods of converting distance Galilean and Keplerian telescopes for near vision. Examples are provided to illustrate the clinical application of these formulas. The information presented here may be helpful when making recommendations concerning the most appropriate method of converting a telescope for near vision.

Humans↗
PubMed2005

Telescopic-assisted radiofrequency adenoidectomy: a prospective randomized controlled trial.

OBJECTIVES/HYPOTHESIS: The objective was to conduct a prospective randomized controlled trial describing and investigating the efficacy and safety of transoral telescopic-assisted radiofrequency adenoidectomy in young children. STUDY DESIGN: Prospective randomized controlled trial. METHODS: One hundred twenty patients who were 36 months of age or less and planned to undergo adenoidectomy or adenoidectomy with insertion of tympanostomy tubes were included in the study. Children were prospectively and randomly assigned into two equal treatment groups: the telescopic-assisted adenoidectomy using radiofrequency curette and the conventional adenoid-curette adenoidectomy. The main parameters included visual analogue scale score for nasal breathing, amount of blood loss, operating time, completeness of adenoid resection, smoothness of postoperative recovery, and complications. RESULTS: Both groups had a significant improvement in the visual analogue scale score after surgery with no evidence for a significant difference between the conventional adenoid-curette and radiofrequency groups. The amount of blood lost during radiofrequency adenoidectomy was minimal, with a mean difference of 31 mL and a median difference of 26 mL. There was a tendency for shorter operative time in the radiofrequency group, but this did not reach a statistical significance. No evidence for a significant difference was noticed in the smoothness of postoperative recovery or complication rate. CONCLUSION: Telescopic-assisted radiofrequency-curette adenoidectomy allows removal of huge adenoids completely in a precise, easy, and cost-effective procedure, with minimal blood loss and short operating time. The use of transoral telescopes provides a clear visualization that helps complete removal of the adenoids, reduction of unnecessary trauma, and effective control of bleeding.

Adenoidectomy↗
PubMed2006

Interferometric coupling of the Keck telescopes with single-mode fibers.

Here we report successful interferometric coupling of two large telescopes with single-mode fibers. Interference fringes were obtained in the 2- to 2.3-micrometer wavelength range on the star 107 Herculis by using the two Keck 10-meter telescopes, each feeding their common interferometric focus with 300 meters of single-mode fibers. This experiment demonstrates the potential of fibers for future kilometric arrays of telescopes and is the first step toward the 'OHANA (Optical Hawaiian Array for Nanoradian Astronomy) interferometer at the Mauna Kea observatory in Hawaii. It opens the way to sensitive optical imagers with resolutions below 1 milli-arc second. Our experimental setup can be directly extended to large telescopes separated by many hundreds of meters.

Journal Article↗
PubMed1983

The telescoping plugged catheter in suspected anaerobic infections. A controlled series.

The results of bacterial cultures from transtracheal aspiration and from aspirations obtained by a new telescoping plugged catheter were compared in specimens taken from 13 patients with suspected anaerobic infections of the lower respiratory tract. When all bacterial isolates (potential aerobic pathogens, aerobic nonpathogens, and anaerobes) were counted with transtracheal aspiration as the standard method for comparison, cultures of material obtained by the telescoping plugged catheter technique yielded 22 false negatives and 14 false positives. The results of the 2 methods were in complete agreement in only 3 paired specimens cultured aerobically and in only 6 paired specimens cultured anaerobically. When only potential aerobic pathogens and anaerobes were considered with transtracheal aspiration as the standard method for comparison, cultures of material obtained by the telescoping plugged catheter technique yielded 11 false negatives and 7 false positives, and the results of the 2 methods were in complete agreement in 9 paired specimens cultured aerobically and 6 paired specimens cultured anaerobically. Our results suggest that fiberoptic bronchoscopy using the telescoping plugged catheter technique may be an acceptable method for collecting specimens from the lower respiratory tract, but further studies comparing this method with transtracheal aspiration are needed.

Adult↗
PubMedDate not supplied

Videolaryngoscopy. A comparison of fiberscopic and telescopic documentation.

Videolaryngoscopy is a most useful and effective method of evaluation and documentation of physiological and pathological conditions of the larynx. It is of great value for making accurate diagnosis and planning proper treatment. It permits instant and simultaneous voice and video recording and later analysis. Videolaryngoscopy can be accomplished with either a flexible fiberscope or a rigid right-angled telescope. Fiberscopic videolaryngoscopy is more useful for voice analysis of speech disorders and evaluation of such functions of the larynx as phonation, singing, and swallowing. Telescopic videolaryngoscopy is superior for critical evaluation of anatomical and pathological changes of the laryngeal structures as well as close-up examination of vocal cord function. While fiberscopic laryngoscopy is technically easy, fiberscopic video documentation is much more difficult than telescopic video documentation. Telescopic videolaryngoscopy provides clearer and sharper images of the larynx. Advantages and disadvantages of each method are discussed.

Female↗
PubMed2002

Phasing segmented mirrors: a modification of the Keck narrow-band technique and its application to extremely large telescopes.

Future telescopes with diameters greater than 10 m, usually referred to as extremely large telescopes (ELTs), will employ segmented mirrors made up of hundreds or even thousands of segments, with tight constraints on the piston errors between individual segments. The 10-m Keck telescopes are routinely phased with the narrow-band phasing technique. This is a variation of the Shack-Hartmann wave-front sensor in which the signal is the correlation between individual subimages and simulated images. We have investigated the applicability of this technique to ELTs, and in the process we have developed what to our knowledge is a new algorithm in which each subimage provides on its own a piston-dependent value. We also discuss an alternative algorithm to resolve the lambda ambiguity that allows detection of problematic cases, and a modification of the singular-value-decomposition procedure used to phase the whole mirror, using weightings on individual measurement errors. By means of simulations we show that the modified technique shows improved performance and that it can work with sufficient precision on telescopes as large as 100 m.

Journal Article↗
PubMed2004

Experimental verification of dispersed fringe sensing as a segment phasing technique using the Keck telescope.

Dispersed fringe sensing (DFS) is an efficient and robust method for coarse phasing of segmented primary mirrors (from one quarter of a wavelength to as much as the depth of focus of a single segment, typically several tens of microns). Unlike phasing techniques currently used for ground-based segmented telescopes, DFS does not require the use of edge sensors in order to sense changes in the relative heights of adjacent segments; this makes it particularly well suited for phasing of space-borne segmented telescopes, such as the James Webb Space Telescope. We validate DFS by using it to measure the piston errors of the segments of one of the Keck telescopes. The results agree with those of the Shack-Hartmann-based phasing scheme currently in use at Keck to within 2% over a range of initial piston errors of +/-16 microm.

Journal Article↗
PubMed2006

Wind loads on ground-based telescopes.

One of the factors that can influence the performance of large optical telescopes is the vibration of the telescope structure due to unsteady wind inside the telescope enclosure. Estimating the resulting degradation in image quality has been difficult because of the relatively poor understanding of the flow characteristics. Significant progress has recently been made, informed by measurements in existing observatories, wind-tunnel tests, and computational fluid dynamic analyses. We combine the information from these sources to summarize the relevant wind characteristics and enable a model of the dynamic wind loads on a telescope structure within an enclosure. The amplitude, temporal spectrum, and spatial distribution of wind disturbances are defined as a function of relevant design parameters, providing a significant improvement in our understanding of an important design issue.

Journal Article↗
PubMed2003

Operation technique and healing process of telescopic ileocolostomy in dogs.

The healing process of telescopic anastomoses was found in an animal experiment with 12 mongrel dogs. After the division of vessels an ileal segment of different length was invaginated into the lumen of the colon using single-layer interrupted sutures. The following four groups were used: Group A (n = 3): end-to-side ileocolostomy, single-layer interrupted suture (invagination length: 0 mm), survival time: 21 days. Group B (n = 3): invagination length: 20 mm, survival time: 7 days. Group C (n = 3): invagination length: 10 mm, survival time: 21 days. Group D (n = 3): invagination length: 20 mm, survival time: 21 days. At the end of the above survival times the anastomosis area was removed. The bursting pressure was measured and morphological as well as histological examinations were performed. In each case the 0-day look-alikes of anastomoses were performed using the remnant bowels, and bursting pressure measurements were done on these models as well. Anastomosis leakage did not occur. The serosal layer of the intracolonic part of the ileum disappeared during the healing process. The free surface of the intracolonic ileal segment became covered by the sliding mucosa of the colon and the prolapsing mucosa of the ileum. The following could be concluded after the experiments: The inner pressure tolerance of a telescopic ileocolostomy promptly after preparation is better than in case of another single-layer anastomosis. This fact results in increased safety against leakage on the first postoperative days. The inner pressure tolerance of the telescopic ileocolostomy increases during the healing process and it does not depend on the length of the invaginated part (0 day-20 mm: 56 mmHg +/- 6, Group A: 252 +/- 39, Group B: 154 +/- 19, Group C: 249 +/- 20, Group D: 298 +/- 2). There is no difference in pressure tolerance between the telescopic and the end-to-side single-layer interrupted anastomoses after the healing process. The invaginated section within the lumen of the large intestine does not suffer ischaemic or any other kind of damage. This inexpensive and simple anastomosis technique could be useful in the veterinary surgical practice as well.

Anastomosis, Surgical↗
PubMed2006

Telescopic crowns as attachments for implant supported restorations: a case series.

The use of dental implants to support mandibular or maxillary overdentures is a widely used treatment modality. Advantages are an increase in retention, an increase in chewing ability, and easy access for oral hygiene procedures. While telescopic and conical crowns have been used for decades to connect natural teeth to overdentures, not many cases have been reported in the literature of telescopic crowns placed on implants to support overdentures. This article describes 7 patients with overdentures supported by telescopic crowns who received 65 implants (ITI Straumann). The cases presented in this report have been in function for up to 4.5 years. During that time no adverse events were reported. The use of telescopic crowns as attachments for implant-supported overdentures may be a viable treatment option.

Adult↗
PubMedDate not supplied

[Effect of the conus telescope system on the periodontal status of abutment teeth in Kennedy class I partial edentulousness].

Periodontal status of abutment teeth of conus telescope system was investigated in the production of telescope prosthesis on two and four abutment teeth in Kennedy class I edentulousness. In the first case, abutment teeth of conus telescope system were the first lower premolars, and in the second case the first lower premolars and canines. All investigations were performed on first lower premolars, and included the follow-up of following indexes and parameters: gingival index, periodontal pocket depth, bone resorption index, abutment teeth mobility and dental plaque index. Investigations were performed in two groups of patients: before and after three months and one year after the prosthetic management. The results of clinical investigations revealed the improvement of all investigated parameters three and twelve months later compared to the state prior to the production of telescope prosthesis.

Aged↗
PubMed1999

Three-dimensional finite element analysis and comparison of stress distribution in overdentures supported with bar attachments and telescopic crowns.

OBJECTIVE: To determine which one of the overdenture (OD) retainers was more beneficial to the abutments--the bar or the telescopic crown--and if a tooth could be used as an OD abutment when the supporting bone decreased to half of the root. MATERIALS AND METHODS: The three-dimensional finite element method was used to investigate the stress distribution in a mandible with an overdenture supported by the roots of two canines. The two teeth were either connected with a bar attachment or restored with telescopic crowns, and were then restored with a complete overdenture. For each type of superstructure, the influence of bone height around the roots (no alveolar resorption and resorption to half of the root length) was analyzed under three loading conditions. RESULTS: The most extreme stress values were located at the alveolar ridge crest of the bone around the root of the abutment. In the case of anterior loading, the largest compressive stress (LCS) in telescopic crown overdenture (TOD) was lower. When loaded posteriorly there was no obvious difference between bar attachment overdenture (BOD) and TOD. At the alveolar ridge crest around the root of the abutment, the stress value in the model with decreased bone level was higher than in the model with normal bone level, but the range was not significant. CONCLUSION: 1. In terms of stress in the alveolar bone, complete overdenture over telescopic crowns is more convenient than over bar attachments. 2. Stress increases as the height of the bone around the roots decreases, but the increment is less than 30%. It is important for an abutment with bone resorption to perform root amputation to obtain an acceptable crown/root ratio.

Alveolar Bone Loss↗
PubMed2002

Ergonomic benefits of surgical telescope systems: selection guidelines.

A longstanding myth holds that chronic neck and back discomfort or pain is a necessary evil of practicing dentistry. The use of properly selected surgical telescopes and co-axial illumination headlights has been demonstrated to prevent or in some cases eliminate chronic neck and back pain. This paper will discuss the ergonomic benefits of surgical telescopes and co-axial illumination lights, the recent advances made in surgical telescope technology, and practical guidelines for selecting telescopes.

Back Pain↗
PubMed2002

Laboratory study on abutment movement of the combined clasp, the extension clasp and the telescopic crown.

OBJECTIVE: To study the influence of three kinds of retainers on the abutment movement of removable partial dentures (RPDs) for restoring the dentition with unilateral distal-extended tooth missing. METHODS: The combined clasp, the extension clasp and the telescopic crown were designed to retain RPDs. When food chip was masticated between dentitions, the displacement of abutments was measured by a high-sensitive-laser-transferring-detector, and then the data was statistically analyzed. RESULTS: All of abutments showed the inclination, torsion and vertical translocation. Of them, abutments with telescopic crowns had the lowest horizontal torsion (P < 0.01) and the highest vertical translocation (P < 0.01). CONCLUSIONS: Compared with the combined clasp and the extension clasp, the telescopic crowns enable abutments to bear the load more axial and the stress to be distributed more even, so the design of the telescopic crown may be considered more favourable for the health of abutments.

Crowns↗