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At least 433 records · Page 24Linked to original sources
PubMed1993

Evaluation of contrast acuity and defocus curve in bifocal and monofocal intraocular lenses.

We compared visual quality of the following intraocular lenses in a prospective study: monofocal, True Vista bifocal, 3M diffractive bifocal, and Nordan aspheric VariFocal silicone. Four to six months postoperatively we measured distance acuity, Snellen near acuity (Lighthouse chart), reading acuity (Nieden chart), and contrast acuity at far and near focus (Regan charts: 96%, 50%, 25%, 11% contrast) with different pupil sizes. A defocus curve was obtained by spectacle defocus (+1 diopter [D] to -5 D). Eleven patients had True Vista in one eye and monofocal in the fellow. Contrast acuity at far focus decreased with decreasing contrast and increasing pupil size. This decrease was more pronounced with the True Vista than with the monofocal lenses. These differences were significant, with a 4.5 mm pupil at lower contrast (25%, P = .02; 11%, P = .01). Depth of focus was 4.5 D (+1.0 D to -2.0 D) with True Vista lenses and 2.5 D (+1.0 D to -1.5 D) with monofocal lenses. Corrected distance acuity was 20/22 with True Vista, 20/25 with 3M, and 20/20 with VariFocal. Distance corrected Snellen near acuity was 20/39 with True Vista, 20/34 with 3M, and 20/57 with VariFocal. Distance corrected reading acuity was 20/29 with True Vista, 20/23 with 3M, and 20/44 with VariFocal (P = .005). Contrast acuity at far focus was best with the VariFocal IOL, followed by True Vista and 3M. At near focus it was best with 3M, followed by True Vista and VariFocal. Contrast acuity at near focus was lower than at far focus. Average acuity differences were as follows: VariFocal 0.43, P = .01; True Vista 0.19, P = .05; 3M 0.04, P = .3. Depth of focus was 4.5 D (+1.0 D to -3.5 D) with True Vista and 3M and was 3 D (+1.0 D to -2.0 D) with VariFocal. Each design offers unique features. VariFocal is best at distance, but near vision is not sufficient. The 3M lens is best at near vision but distance contrast acuity is somewhat reduced. The True Vista lens provides a good compromise as distance contrast acuity is good and near vision is sufficient.

Aged↗
PubMed2000

Association of mild acetabular dysplasia with an increased risk of incident hip osteoarthritis in elderly white women: the study of osteoporotic fractures.

OBJECTIVE: To determine if acetabular dysplasia increases the risk of incident hip osteoarthritis (OA) among elderly white women. METHODS: Baseline and followup anteroposterior pelvic radiographs were obtained a mean of 8 years apart, and read for individual radiographic features (IRFs) of hip OA; summary grades (0-4) were then assigned based on the IRFs present. Acetabular dysplasia was defined by the results of measurements of the acetabular depth (<9 mm) or the center-edge angle (<30 degrees). Logistic regression analyses were performed to determine the association between acetabular dysplasia and incident hip OA, and all analyses were adjusted for age, current weight, body mass index, affected side, and investigational site. RESULTS: The odds ratios for the association of abnormal center-edge angle and acetabular dysplasia with incident hip OA were 3.3 (95% confidence interval 1.1-10.1) and 2.8 (95% confidence interval 1.0-7.9), respectively. CONCLUSION: Acetabular dysplasia, defined by a decrease in the center-edge angle, is associated with a modestly increased risk of incident hip OA in elderly white women.

Acetabulum↗
PubMed2006

Humanities for medical students? A qualitative study of a medical humanities curriculum in a medical school program.

BACKGROUND: Today, there is a trend towards establishing the medical humanities as a component of medical education. However, medical humanities programs that exist within the context of a medical school can be problematic. The aim of this study was to explore problems that can arise with the establishment of a medical humanities curriculum in a medical school program. METHODS: Our theoretical approach in this study is informed by derridean deconstruction and by post-structuralist analysis. We examined the ideology of the Humanities and Medicine program at Lund University, Sweden, the practical implementation of the program, and how ideology and practice corresponded. Examination of the ideology driving the humanities and medicine program was based on a critical reading of all available written material concerning the Humanities and Medicine project. The practice of the program was examined by means of a participatory observation study of one course, and by in-depth interviews with five students who participated in the course. Data was analysed using a hermeneutic editing approach. RESULTS: The ideological language used to describe the program calls it an interdisciplinary learning environment but at the same time shows that the conditions of the program are established by the medical faculty's agenda. In practice, the "humanities" are constructed, defined and used within a medical frame of reference. Medical students have interesting discussions, acquire concepts and enjoy the program. But they come away lacking theoretical structure to understand what they have learned. There is no place for humanities students in the program. CONCLUSION: A challenge facing cross-disciplinary programs is creating an environment where the disciplines have equal standing and contribution.

Curriculum↗
PubMed1985

A comparison of sector and linear array scanners for the measurement of the fetal femur.

This study was designed to determine whether differences between sector and linear array scanners introduce variability in fetal femur length measurements, used to determine gestational age. Twenty transducers from 15 machines were tested with the manufacturers' approval. Machines were coded to maintain anonymity. Three different sized sections of plastic straws were scanned in a water bath. All measurements were made by the same investigator. Measurements were adjusted to compensate for the difference in sound velocity in water, which introduced a 3.36 per cent error in apparent depth of the image for linear array scanners, and a 3.36 per cent error in apparent depth and length for sector scanners. A large variation in measurements was obtained, although the differences were usually within acceptable limits (approximately 4 per cent). Linear array scanners were found to give similar readings as sector scanners.

Embryonic and Fetal Development↗
PubMed1988

Aesthesiometric threshold changes over the course of a workshift in miners exposed to hand-arm vibration.

The objective of this study was to investigate whether aesthesiometric threshold changes occur over the course of a workshift in vibration exposed hard rock miners relative to workers unexposed to vibration during the shift. The subjects were 99 miners and 40 smelter workers; four subjects declined to participate and nine were excluded from the analysis because of apparent failure to comprehend the testing procedure. Two point discrimination and depth sense aesthesiometry were conducted at the beginning and at the end of the workshift in all digits of both hands excluding the thumbs. In addition to the use of a vibrating tool during the shift, age, digital temperature, signs of arm injury, presence of fingertip callus, and handedness were documented. In the analysis the difference between postshift and preshift readings was studied in relation to these variables, particularly exposure to the jackleg drill during the shift. With the exception of exposure of the jackleg drill, no associations were observed between these variables and change over the workshift in aesthesiometric results, on both unadjusted comparison of means and backward elimination regression analysis. A statistically significant association, however, was found between the use of a jackleg drill and change in two point discrimination and in depth sense aesthesiometric results over the course of the shift, for the right hand. Evidence of the occurrence of a learning effect, particularly for two point discrimination aesthesiometry, was observed. The occurrence of an effect in the right, but not the left, hand reflects dominant handedness and relatively greater vibration exposure in the right hand in our subjects. This study supports the incorporation of an exposure free interval before aesthesiometric testing of vibration exposed workers.

Fingers↗
PubMedDate not supplied

Burn depth evaluation with fluorometry: is it really definitive?

Clinical evaluation of burn depth soon after injury is subjective, based on gross visual assessment. Previous investigators have quantified this process using fluorometry. Their studies show fluorescein levels in full-thickness burns to be far below control levels and partial-thickness burns to be about 60% of nonburned skin. In both rat and human models, 59 burn sites (eight rats) and 37 burn sites (seven patients) were assessed. Readings were taken for three hours on the rats and one hour on the patients during the first 48 hours, and the procedure was repeated for five days postburn. Maximum values during these periods were determined for burn and nonburn sites, and background levels were subtracted from these values. The rate of fluorescein uptake and the peak times for burn and nonburn sites were then compared. Actual depth of burn was determined by whether or not healing had occurred. The results showed no significant difference between partial-thickness and full-thickness burns using fluorometry, as standard deviations in both models for both depths of burn were large. Therefore, fluorometry did not provide a definitive evaluation of burn depth. These results differ from those reported by previous investigators.

Animals↗
PubMedDate not supplied

Partial-thickness burns: identification and management.

PURPOSE: To provide an overview of the appropriate evaluation and management of partial-thickness burns. TARGET AUDIENCE: This continuing-education activity is intended for physicians and nurses with an interest in learning about burn wound care. LEARNING OBJECTIVES: After reading the article and taking the test, the participant will be able to: 1. Describe the classification of burn wounds. 2. Identify characteristics of burn wounds and the clinical techniques for diagnosing burn wound depth. 3. Identify the treatment options for partial-thickness burns.

Burn Units↗
PubMed1996

TLD extrapolation for skin dose determination in vivo.

Prediction of skin reactions requires knowledge of the dose at various depths in the human skin. Using thermoluminescence dosimeters of three different thicknesses, the dose can be extrapolated to the surface and interpolated between the different depths. A TLD holder was designed for these TLD extrapolation measurements on patients during treatment which allowed measurements of entrance and exit skin dose with a day to day variability of +/-7% (S.D. of mean reading). In a pilot study on 18 patients undergoing breast irradiation, it was found that the angle of incidence of the radiation beam is the most significant factor influencing skin entrance dose. In most of these measurements the beam exit dose contributed 50% more to the surface dose than the entrance dose.

Breast Neoplasms↗
PubMed1997

[Limbus-parallel keratotomies with compression sutures in treatment of high astigmatism after perforating keratoplasty: a vector analysis and topographic study].

BACKGROUND: Visual acuity following penetrating keratoplasty is frequently limited by excessive astigmatism which cannot be compensated for with spectacles or contact lenses. The purpose of the study was to determine the effects of arcuate keratotomies and compression sutures on the amount and regularity of corneal astigmatism and on the visual acuity. PATIENTS AND METHODS: Between June 1989 and August 1995, 56 eyes from 56 patients (30 women, 26 men, average age 53 +/- 16 years) with excessive post-penetrating keratoplasty astigmatism were treated with paired arcuate cuts and compression sutures 4.8 +/- 3.5 years after suture removal (45% keratoconus, 30% scars, 20% dystrophies). The incisions were made along the meridian of maximum dioptric power in a sector extending for 60 +/- 15 degrees (6 mm diameter). Incision depth was standardized at 450 microns. Compression sutures were placed 90 degrees away in the flat meridian. Eight patients required more than one procedure to obtain the desired effect. Best corrected visual acuity (VA), keratometric readings and topographic power maps were analyzed pre- and postoperatively. We categorized the topographic maps into six groups: from group 1 (regular) to group 6 (irregular). For description of the astigmatic change after surgery, the formulas by Naylor and Jaffe (vector-corrected astigmatism) were applied. RESULTS: The mean preoperative astigmatism was 10.8 +/- 3.1 (4.2 to 19.2) diopters (D). After a mean follow-up of 1.1 years, the mean net astigmatism was 5.8 +/- 3.2 (0 to 16) D. The mean preoperative visual acuity (VA) was 0.38 +/- 0.31 (from 0.03 to 1.0). At the end of follow-up, the mean VA was 0.43 +/- 0.25. Non-refractive reasons for poor visual acuity included amblyopia (n = 5), macular degeneration (n = 4), glaucoma (n = 4), cataract (n = 2), and others (n = 5). Twenty-seven percent of the preoperative topographic maps were categorized into groups 1 and 2 and only 10% into groups 5 and 6. At the end of the follow-up, none of the 53 available topographic maps was categorized into group 1, 7.5% into group 2 and 30% into groups 5 and 6. The mean astigmatic change (vector-corrected astigmatism) was 12.3 +/- 5.2 (1.0 to 29.8) D with a turn of the axes ranging from -39 to 44 degrees. CONCLUSIONS: Arcuate incisions with compression sutures are easily performed and hold a low complication rate in comparison with other refractive operations. Definition of successful surgery is even broader when a significant reduction of astigmatism that usually allows the use of spectacles or contact lenses is considered. A disadvantage is that each particular case is unpredictable because of the tendency of the topography to irregularity and possible regression of the effect.

Adult↗
PubMed1996

Improved accuracy of burn wound assessment using laser Doppler.

The utility of the laser Doppler for determining burn depth has been questioned because of problems with technology and methodology. This study prospectively evaluates the ability of a new laser Doppler technique to predict burn healing time. Using the Periflux System 4000 laser Doppler, readings were taken on 305 burns (147 patients) on postburn day 3 or 4. Sixty-six wounds were used to derive a predictive function (phase I) and 152 wounds were used to test the function (phase II). Blood flow dynamics (flux), microvascular dilation capacity of the wounds to beat stress, and flow motion wave pattern (vasomotion) were studied using the laser Doppler, and seven parameters were evaluated to determine their relative contribution to the prediction of healing time. These parameters are hyperemic flux (flux value after heating to 42 degrees C), average hyperemic wave amplitude (AHWA), number of average flux units >100(F100), number readings with wave amplitude 75 (A5), average flux change (AFC), percentage of average flux increase, and relative flow capacity (RFC = AFC/average hyperemic flux). After readings were made, the wounds were observed and divided into two groups: those that healed in less than 14 days and those that healed or were grafted after 14 days. A step-wise discriminant analysis was used to assess the relative contribution of the Doppler-derived measures to healing time prediction. AHWA, F100, and RFC were included in the final discriminant function explaining 72% of the healing time variance (Wilks' lambda value 0.28; p value <0.0001). Predicted outcome = 0.05(AHWA) + 0.31(F100) + 5.0(RFC) - 2.3. With this derived function, there is 94% accuracy in the prediction of burn wound healing time compared with a physician predictive accuracy of 70%.

Adolescent↗
PubMed1998

Using a colorimeter to develop an intrinsic silicone shade guide for facial prostheses.

PURPOSE: To determine if using CIE L*a*b* color measurements of white facial skin could be correlated to those of silicone shade samples that visually matched the skin. Secondly, to see if a correlation in color measurements could be achieved between the silicone shade samples and duplicated silicone samples made using a shade-guide color formula. MATERIALS AND METHODS: A color booth was designed according to ASTM specifications, and painted using a Munsell Value 8 gray. A Minolta colorimeter was used to make facial skin measurements on 15 white adults. The skin color was duplicated using custom-shaded silicone samples. A 7-step wedge silicone shade guide was then fabricated, representing the commonly encountered thicknesses when fabricating facial prostheses. The silicone samples were then measured with the Minolta colorimeter. The readings were compared with the previous L*a*b* readings from the corresponding patient's skin measurements, and the relative color difference was then calculated. Silicone samples were fabricated and analyzed for three of the patients to determine if duplication of the visually matched silicone specimen was possible using the silicone color formula, and if the duplicates were visually and colorimetrically equivalent to each other. The color difference Delta E and chromaticity was calculated, and the data were analyzed using a coefficient-of-variation formula expressed by percent. A Pearson Product Moment Correlation Coefficient was performed to determine if a correlation existed between the skin and the silicone samples at the p < or = .05 level. RESULTS: The highest correlation was found in the b* dimension for silicone thicknesses of 1 to 4 mm. For silicone thicknesses of 6 to 10 mm, the highest correlation was found in the L* dimension. All three dimensions had positive correlations (R2 > 0), but only the 1-mm and 4-mm b* readings were very strong. Patient and silicone L*a*b* measurement results showed very little change in the a* axis, while the L* and b* measurements showed more change in their numbers, with changes in depth for all patient silicone samples. Delta E numbers indicated the lowest Delta E at the 1-mm depth and the highest Delta E at the 10-mm depth. All duplicated samples matched their original silicone samples to a degree that visual evaluation could not distinguish any color differences. Using volumetric measurements, a shade guide was developed for all 15 patients. CONCLUSIONS: There was good correlation between the patient's colorimeter measurements and the silicone samples, with the b* color dimension the most reproducible, followed by the L* and the a*. Silicone samples at 6, 8, and 10 mm matched the patient the best, and this study showed that silicone samples can be duplicated successfully if a good patient-silicone match is obtained. Rayon flocking fibers and liquid makeup are effective at matching facial prostheses and can be used to develop a simple shade guide for patient application.

Color↗
PubMed2002

A pilot study. Depth perception and near stereoacuity: is it related to academic performance in young children?

PURPOSE: A study of the relationship between an overall measure of visual function at near, specifically stereoacuity, and academic performance in kindergarten through second grade was conducted. METHOD: One hundred seventeen children (mean age = 7.33 +/-0.97 years) from a middle class, suburban, elementary school participated in this masked investigation. The Randot 2 stereotest was used to measure stereoacuity at 40 cm. The relationship between stereoacuity and teachers' personal ratings of academic ability was analyzed because teachers' grades are a primary means of assessing school performance. The children's regular classroom teachers rated the children with respect to reading, mathematics, and writing ability. Children in the second grade (n = 47) were also rated on spelling ability. Only experienced teachers were included in the investigation and the validity of the teachers' rating was substantiated by significant correlations with standardized test scores. Teachers were masked to performance on the stereotest. RESULTS: Performance on the Randot was found to be "statistically significantly" (p=<0.05) and "medically-clinically significantly" related to standardized reading test scores (p=0.033) and teachers' personal ratings of reading (p<0.001), mathematics (p<0.001), writing (p<0.001) and spelling (p=0.048) ability. CONCLUSION: Good visual function at near, particularly good stereoacuity, is significantly correlated to academic performance.

Achievement↗
PubMed1989

Presbyopia correction and the accommodation in reserve.

One method of determining the additional correction for presbyopia suggests leaving a percentage of the amplitude of accommodation in reserve. The rationale for this assumption seems logical because using all of the available accommodation is not sustainable without discomfort. However there is no empirical evidence indicating what percentage of the amplitude of accommodation should actually be left in reserve. Common figures adopted have been one-half and one-third. In this investigation the percentage of accommodation used is deduced mathematically after having determined the following: 1. The 'add' by the direct subjective clinical method. 2. Measured the amplitude of accommodation. 3. Measured the reading distance in 305 presbyopes ranging from 40 to 83 years of age. The results showed a small decline in the amplitude of accommodation up to the age of 52, after which age the measurements were scattered about a steady level. This finding suggests that after the age of 52 the results are based on the depth-of-focus of the eye. Females had slightly greater accommodation than males of the same age. The power of the add was significantly correlated to the age of the subject. The mean percentage of accommodation used for the 305 subjects was found to be 50.7%, thus confirming the rule of leaving half of the accommodation in reserve, although there were large variations: there were differences between males and females and with age the percentage of measured accommodation used, after having determined the correct add, diminished. Similarly the percentage of accommodation also decreased for shorter reading distances.

Accommodation, Ocular↗
PubMed2002

Transsaccadic memory for visual object detail.

When we move our eyes around in real-world scenes, we typically have several peripheral previews of an object before we direct our eyes straight at the object. Numerous studies on transsaccadic memory have investigated whether there is any evidence for the integration of peripheral object information acquired presaccadically with foveal object information acquired postsaccadically. We review this evidence to illustrate the currently dominant view that transsaccadic object memory is sparse and contains little visual object detail. However, based on some recent studies of the role of postsaccadic stimulus blanking in transsaccadic change detection, we hypothesize that transsaccadic object memory involves the automatic emergence of a visual analog: a high-capacity, non-selective, internal representation of visual object detail. This hypothesis is tested by examining cued detection of intrasaccadic changes in the in-depth orientation of objects in scenes. The data provide preliminary support for the presence of the visual analog, but also show that its functionality is strictly limited by attentional and temporal constraints on the process of reading out information from the visual analog.

Cues↗
PubMed1991

Breast conservation, the problem of treating the excision site effectively: physical criteria for the choice of technique used.

This paper examines how physical factors such as the depth of the excision cavity below the skin surface and its distance from the underlying lung may impact upon the choice between the use of an electron field (from a Varian Clinac 1800) or an implant (using a double plane of iridium-192 wires). Data have been derived from a phantom dosimetry experiment simulating different permutations of breast size and depth of excision cavity. An anthropomorphic female phantom with two different-sized wax breast phantoms has been used to simulate the clinical circumstances envisaged and isodose distributions have been estimated from an array of TLD readings. The biological significance of doses measured in skin and lung have been examined using the linear-quadratic (LQ) model. Both on physical and biological grounds, the results favour the implant under the experimental conditions adopted. The use of the electron beam to definitively treat the excision cavity (omitting breast tangents) to 60 Gy would result in unacceptable late effects in the skin and an observable incidence of pneumonitis if the excision cavity were near the chest wall. Small carcinogenic risks, particularly to the lung, are apparent with each modality, but may be moderated for the iridium-192 implant by a reduced carcinogenic potential associated with low-dose rate radiation. The use of the newer radionuclides iodine-125 and samarium-145, with less penetrating gamma ray emissions, might be preferred to iridium-192 from the point of view of bronchial carcinogenesis if definitive treatment of the excision cavity became widespread practice.

Brachytherapy↗
PubMed2006

Characterization of the phantom material virtual water in high-energy photon and electron beams.

The material Virtual Water has been characterized in photon and electron beams. Range-scaling factors and fluence correction factors were obtained, the latter with an uncertainty of around 0.2%. This level of uncertainty means that it may be possible to perform dosimetry in a solid phantom with an accuracy approaching that of measurements in water. Two formulations of Virtual Water were investigated with nominally the same elemental composition but differing densities. For photon beams neither formulation showed exact water equivalence-the water/Virtual Water dose ratio varied with the depth of measurement with a difference of over 1% at 10 cm depth. However, by using a density (range) scaling factor very good agreement (<0.2%) between water and Virtual Water at all depths was obtained. In the case of electron beams a range-scaling factor was also required to match the shapes of the depth dose curves in water and Virtual Water. However, there remained a difference in the measured fluence in the two phantoms after this scaling factor had been applied. For measurements around the peak of the depth-dose curve and the reference depth this difference showed some small energy dependence but was in the range 0.1%-0.4%. Perturbation measurements have indicated that small slabs of material upstream of a detector have a small (<0.1% effect) on the chamber reading but material behind the detector can have a larger effect. This has consequences for the design of experiments and in the comparison of measurements and Monte Carlo-derived values.

Electrons↗
PubMed1994

Quantitative measurements of blood flow velocity in basal cerebral arteries with transcranial duplex color-flow imaging. A comparative study with conventional transcranial Doppler sonography.

Transcranial duplex color-flow imaging is a new diagnostic method that allows visual display of blood flow in the basal cerebral arteries. This method allows determination of and correction for the Doppler angle of insonation. Conventional transcranial Doppler sonography has no imaging component and assumes a 0-degree Doppler angle for the calculation of flow velocities. The magnitude of the angle of insonation and the effect on flow velocity estimates have not been clearly defined. In order to evaluate the angle of insonation and the effect of angle correction on velocity readings, 50 patients referred for evaluation of cerebrovascular disease were studied. The mean age was 45 years (range, 24-62 yr). All were examined with conventional transcranial Doppler and transcranial duplex color-flow imaging. Specific vessels of the circle of Willis were identified by location, course, and direction of flow on color-flow images and by depth, direction of flow, and transducer orientation with conventional Doppler sonography. Visually controlled measurements of the Doppler angle of insonation were made by color-flow imaging. The data show that the mean angle of insonation was 33 degrees (+/- 15) in the middle cerebral artery, 35 degrees (+/- 17) in the anterior cerebral artery, 45 degrees (+/- 18) in the posterior cerebral artery, and 15 degrees (+/- 14) in the basilar artery. Angle-corrected peak systolic flow velocities were higher in all vessel segments (middle cerebral = 15%, anterior cerebral = 18%, posterior cerebral = 30%, and basilar = 3%), compared to uncorrected velocity readings by conventional Doppler sonography.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗