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PubMed2002

Use of distance education in dental hygiene programs.

The prevalence of distance education is steadily increasing in institutions of higher education in the United States and abroad. Colleges and universities are seeking new avenues to deliver curricula to students in remote areas and/or to nontraditional students. Distance education is a relatively new venture for dental hygiene education. The purpose of this study was to determine the prevalence and use of distance education in dental hygiene educational programs nationally. Dental hygiene directors of all associate degree and baccalaureate degree dental hygiene programs in the United States (N = 255) were mailed a fifteen-item survey regarding their use of distance education. Results of the study indicated that 22 percent of dental hygiene programs have implemented distance education. In addition, a large variety of courses are being offered by several distance education delivery methods. Thirty of the thirty-eight dental hygiene programs that responded to the survey reported that they were satisfied with their distance education initiatives. The length of time that distance education was offered by the dental hygiene program was not related to satisfaction level (p = .0795), and there was no relationship between the type of distance education used and satisfaction level (p > .05). Considering all factors involved in this study, we can conclude that distance education is being used in a substantial number of dental hygiene programs and that the majority of these programs are satisfied that distance education is an adequate alternative to traditional "brick and mortar" approaches.

Attitude↗
PubMed2003

Optimal distance for segmental nerve conduction studies revisited.

In 1972, Maynard and Stolov showed that the experimental error in calculating nerve conduction velocity (NCV) depends on errors of latency and distance measurements. Their data suggested that a minimum distance of 10 cm should be used when calculating NCV because of an increase in error >/= 25% at shorter distances. The object of this study was to reestablish the minimum distance using current technology. Twenty physicians measured the proximal and distal onset latencies of the same stored ulnar compound muscle action potentials, as well as the forearm skin distance. The mean and standard deviation of the errors in conduction time and distance were determined. A spreadsheet was constructed, determining the error in NCV for a variety of distances and NCVs. The average conduction time between proximal and distal stimulation was 3.23 ms, with a standard deviation of 0.09 ms. The mean distance measurement was 212.6 +/- 2.1 mm. The errors in NCV were significantly less than previously reported. The experimental error increased as distance decreased, reaching 20% with distances less than 6 cm. The latency error accounted for 71% of the total experimental error, as opposed to 90% in the previous study. With advances in electrodiagnostic equipment, NCV can reasonably be calculated at distances less than 10 cm, perhaps as low as 5-6 cm.

Action Potentials↗
PubMed1998

Accuracy of auditory distance and azimuth perception by a passerine bird in natural habitat.

Small birds should localize sound poorly because small head size limits azimuth resolution and because the loose correlation of acoustic degradation with distance limits accurate estimation of auditory distance. We determined the accuracy of sound localization by a passerine bird in the field using an open-loop phonotaxis experiment. After hearing a playback of a conspecific contact call, eastern towhees, Pipilo erythrophthalmus, approached the silenced source. Mean auditory distance resolution was 7% of total speaker distance and mean azimuth resolution was +/-5 degrees. In a second experiment, we played birds the same calls rerecorded previously over the 10- or 20-m distance beyond each playback location. In 13 of 30 trials, the birds over-flew the speaker by a distance propotional to rerecording; but in 15 trials, approach distances were comparable to speaker distance despite the addition of distance simulated by attenuating and rerecording the calls. Signal-specific and location-specific distance cues are derived to explain the bimodal distribution of flight distances we observed. Copyright 1998 The Association for the Study of Animal Behaviour

Journal Article↗
PubMed2000

Is travel distance a barrier to veterans' use of VA hospitals for medical surgical care?

Lengthy travel distances may explain why relatively few veterans in the United States use VA hospitals for inpatient medical/surgical care. We used two approaches to distinguish the effect of distance on VA use from other factors such as access to alternatives and veterans' characteristics. The first approach describes how disparities in travel distance to the VA are related to other characteristics of geographic areas. The second approach involved a multivariate analysis of VA use in postal zip code areas (ZCAs). We used several sources of data to estimate the number of veterans who had priority access to the VA so that use rates could be estimated. Access to hospitals was characterized by estimated travel distance to inpatient providers that typically serve each ZCA. The results demonstrate that travel distance to the VA is variable, with veterans in rural areas traveling much farther for VA care than veterans in areas of high population density. However, Medicare recipients also travel farther in areas of low population density. In some areas veterans must travel lengthy distances for VA care because VA hospitals which were built over the past few decades are not located close to areas in which veterans reside in the 1990s. The disparities in travel distance suggest inequitable access to the VA. Use of the VA decreases with increases in travel distance only up to about 15 miles, after which use is relatively insensitive to further increases in distance. The multivariate analyses indicate that those over 65 are less sensitive to distance than younger veterans, even though those over 65 are Medicare eligible and therefore have inexpensive access to alternatives. The results suggest that proximity to a VA hospital is only one of many factors determining VA use. Further research is indicated to develop an appropriate response to the needs of the small but apparently dedicated group of VA users who are traveling very long distances to obtain VA care.

Aged↗
PubMed2000

Cancer incidences in Europe related to mortalities, and ethnohistoric, genetic, and geographic distances.

We have previously shown that geographic differences in cancer mortalities in Europe are related to (in order of importance): geographic distances (reflecting environmental differences), ethnohistoric distances (encompassing cultural and genetic attributes), and genetic distances of the populations in the areas studied. In this study, we analyzed the relations of the same three factors to European incidences of 45 male and 47 female cancers. Differences in cancer incidences are correlated moderately, first with geographic distances, and then with genetic distances, but not at all with ethnohistoric distances. Comparing these findings to the earlier ones for cancer mortalities, we note the reversal in the importance of ethnohistory and genetics, and the generally lower correlations of incidence differences with the three putatively causal distance matrices. A path diagram combining both studies demonstrates the lack of cultural carcinogenic effects, but suggests cultural influences on procedures such as the registration of deaths in different political entities. Additionally, the relatively large correlation between ethnohistoric distances and mortality differences is caused by common factors behind the correlation of ethnohistoric and geographic distances. Geographic proximity results in similar ethnohistories. The direct effects of genetic distances are negligible and only their common effects with geographic distances play a role, accounting for the weak to negligible influence of genetics on incidence and mortality differences. Apparently, the genetic systems available to us do not substantially affect cancer incidence or mortality. We present indirect evidence that international differences in the quality of cancer rate data are greater in mortalities than in incidences.

Cluster Analysis↗
PubMed1982

The mathematics of mosaic analysis. I: The relationship between sturts and distance.

In mosaic fate mapping the fraction of mosaics in which two structures are of different genotype is calculated. This frequency of separation has been called a "distance" and the units of this distance are called "sturts". The fundamental assumption of fate mapping is that the frequency of separation increases continuously with the actual distance between the anlage for these structures on the blastoderm. This paper shows that the frequency of separation does not increase beyond a certain value. --For the current theory to work as proposed, each mosaic animal must be half mutant and half normal. This is rarely the case in collections of mosaics. It has been thought that if some flies are less than half mutant and others more than half, these two types would introduce compensating errors in mapping distance. We show that this is not true and describe the nature of the errors introduced. It is probable that these errors are the main reason that mapping distances reported from different sets of mosaics have not been reproducible. This paper presents methods for the proper handling of data from mosaics with different amounts of mutant tissue.--We prove here that for mosaics with an arbitrary fraction of mutant tissue (m), the largest frequency of separation that can occur is 2m. We prove that sturts underestimate actual distance on the blastoderm by a factor of r/m, where r is the radius of the mutant patch, and that sturts give no information on distances greater than 2r. This, and not double crossing over, is the reason for the nonadditivity of sturts and the shrinking of large distances in sturt measures. Sturtoids overestimate distances by a factor of 1/(2r) and also give no information on distances over 2r. This paper gives formulae for correctly estimating distance when using a collection of mosaics with varying amounts of mutant tissue. We also describe the nature of the errors introduced by convoluted or elongate mosaic boundaries and by multiple mosaic patches.

Animals↗
PubMed1998

The effect of distance from home on attendance at a small rural health centre in Papua New Guinea.

BACKGROUND: The willingness of patients in the rural tropics to seek medical care at primary health care facilities is influenced by the distance they have to travel, but few studies have tried to estimate these distance effects. METHODS: Distance decay effects in attendance rates were estimated from a database of 4348 attendances at a rural health centre in Papua New Guinea, linked to demographic and house position data for the catchment population. Small-scale spatial patterns and differences between diagnoses, age groups and gender are described. RESULTS: Attendance decreased markedly with distance both overall (50% decrease at 3.5 km) and for patients with malaria or acute respiratory infections. This decrease was non-linear (on log scale) with distance. Although constant over time, there were big differences in this distance effect among age and gender groups: Female patients showed less distance decay in adolescents and adults, but higher in the infant group. Spatial patterns accounted for 32% of the variation in age- and gender-specific attendance rates. Of the spatial effects more than 50% were due to distance effects. CONCLUSIONS: Distance effects were similar in magnitude to those reported elsewhere, suggesting that distance effects may be generalizable to many parts of the rural tropics. The non-linearity of distance decay implies that a bell-shaped demand function should be used in health planning.

Adolescent↗
PubMed1997

Evolutionary distances between nucleotide sequences based on the distribution of substitution rates among sites as estimated by parsimony.

The rate of evolution of macromolecules such as ribosomal RNAs and proteins varies along the molecule because structural and functional constraints differ between sites. Many studies have shown that ignoring this variation in computing evolutionary distances leads to severe underestimation of sequence divergences, and thus can lead to misleading evolutionary tree inferences. We propose here a new parsimony-based method for computing evolutionary distances between pairs of sequences that takes into account this variation and estimates it from the data. This method applies to the number of substitutions per site in ribosomal RNA genes as well as to the number of nonsynonymous substitutions per codon for protein-coding genes and is especially suitable when large data sets (> or = 100 sequences) are analyzed. First, starting from a phylogeny constructed with usual distances, the maximum-parsimony method is used to infer the distribution of the number of substitutions that have occurred at each site (or codon) along this tree. This distribution is then fitted to an "invariant + truncated negative binomial" distribution that allows for invariant sites. Maximum-likelihood fitting of this distribution to different data sets showed that it agreed very well with real data. Noticeably, allowing for invariant sites seemed to be very important. Finally, two distance estimates were developed by introducing the distribution of site variability into the substitution models of Jukes and Cantor and of Kimura. The use of different numbers of aligned sequences (up to 1,000 rRNA sequences) showed that the parameters of the model are very sensitive to the number of sequences used to estimate them. However, if at least 100 sequences are considered, the two new distance estimates are quite stable with respect to the number of sequences used to fit the distribution. This stability is true for low as well as for high evolutionary distances. These new distances appeared to be much better estimates of the number of substitutions per site than the classical distances of Jukes and Cantor and of Kimura, which both greatly underestimate this number, so that they can serve as indexes to detect saturation. We conclude that the new distances are particularly suitable for phylogenetic analysis when very distantly related species and relatively large data sets are considered. Trees reconstructed using these distances are generally different from those constructed by means of the classical estimates. Using this new method, we showed that the mean evolutionary distance between Prokaryotes and Eukaryotes is substantially higher for the small-subunit than for the large-subunit rRNAs. This suggests than the former might have experienced a drastic change during the early evolution of Eukaryotes.

Algorithms↗
PubMed2001

An in vitro mouse model of cleft palate: defining a critical intershelf distance necessary for palatal clefting.

It is unclear whether cleft palate formation is attributable to intrinsic biomolecular defects in the embryonic elevating palatal shelves or to an inability of the shelves to overcome a mechanical obstruction (such as the tongue in Pierre Robin sequence) to normal fusion. Regardless of the specific mechanism, presumably embryonic palatal shelves are ultimately unable to bridge a critical distance and remain unapproximated, resulting in a clefting defect at birth. We propose to use a palate organ culture system to determine the critical distance beyond which embryonic palatal shelves fail to fuse (i.e., the minimal critical intershelf distance). In doing so, we hope to establish an in vitro cleft palate model that could then be used to investigate the contributions of various signaling pathways to cleft formation and to study novel in utero treatment strategies. Palatal shelves from CD-1 mouse embryos were microdissected on day 13.5 of gestation (E13.5; term = 19.5 days), before fusion. Using a standardized microscope ocular grid, paired palatal shelves were placed on a filter insert at precisely graded distances ranging from 0 (in contact) to 1.9 mm (0, 0.095, 0.19, 0.26, 0.38, 0.48, 0.57, 0.76, 0.95, and 1.9 mm). A total of 68 paired palatal shelves were placed in serum-free organ culture for 96 hours (n = 68). Sample sizes of 10 were used for each intershelf distance up to and including 0.48 mm (n = 60). For intershelf distances of 0.57 mm and greater, two-paired palatal shelves were cultured (n = 8). All specimens were assessed grossly and histologically for palatal fusion. Palatal fusion occurred in our model only when intershelf distances were 0.38 mm or less. At 0.38 mm, eight of 10 palates appeared grossly adherent, whereas six of 10 demonstrated clear fusion histologically with resolution of the medial epithelial seam and continuity of the palatal mesenchyme. None of the 18 palates fused when placed at intershelf distances of 0.48 mm or greater. Using our selected intershelf distances as a guideline, we have established an approximate minimal critical intershelf distance (0.48 mm) at which we can reliably expect no palatal fusion. Culturing palatal shelves at intershelf distances of 0.48 mm or greater results in nonfusion or clefting in vitro. This model will allow us to study biomolecular characteristics of unfused or cleft palatal shelves in comparison with fused shelves. Furthermore, we plan to study the efficacy of grafting with exogenous embryonic mesenchyme or candidate factors to overcome clefting in vitro as a first step toward future in utero treatment strategies.

Animals↗
PubMed2003

Distance and reverberation effects on directional benefit.

OBJECTIVE: Understanding the potential benefits and limitations of directional hearing aids across a wide range of listening environments is important when counseling persons with hearing loss regarding realistic expectations for these devices. The purpose of this study was to examine the impact of speaker-to-listener distance on directional benefit in two reverberant environments, in which the dominate noise sources were placed close to the hearing aid wearer. In addition, speech transmission index (STI) measures made in the test environments were compared to measured sentence recognition to determine if performance was predictable across changes in distance, reverberation and microphone mode. DESIGN: The aided sentence recognition, in noise, for fourteen adult participants with symmetrical sensorineural hearing impairment was measured in six environmental conditions in both directional and omnidirectional modes. A single room, containing four uncorrelated noise sources served as the test environment. The room was modified to exhibit either low (RT60 = 0.3 sec) or moderate (RT60 = 0.9 sec) levels of reverberation. Sentence recognition was measured in both reverberant environments at three different speech loudspeaker-to-listener distances (1.2 m, 2.4 m, and 4.8 m). STI measures also were made in each of the 12 listening conditions (2 microphone modes x 3 distances x 2 reverberation environments). RESULTS: A decrease in directional benefit was measured with increasing distance in the moderate reverberation condition. Although reduced, directional benefit was still present in the moderately reverberant environment at the farthest speech speaker-to-listener distance tested in this experiment. A similar decrease with increasing speaker-to-listener distance was not measured in the low reverberation condition. The pattern of average sentence recognition results across varying distances and two different reverberation times agreed with the pattern of STI values measured under the same conditions. CONCLUSIONS: Although these data support increased directional benefit in noise for reduced speaker-to-listener distance, some benefit was still obtained by listeners when listening beyond "effective" critical distance under conditions of low (300 msec) to moderate (900 msec) reverberation. It is assumed that the directional benefit was due to the reduction of the direct sound energy from the noise sources near the listener. The use of aided STI values for the prediction of average word recognition across listening conditions that differ in reverberation, microphone directivity, and speaker-to-listener distance also was supported.

Adult↗
PubMed1996

Changes in stroke distance in response to haemorrhage in a swine model.

OBJECTIVE: To determine, using an animal model of blood loss, (1) if stroke distance, derived non-invasively from the time integral of the maximum velocity of red cells in the aorta, changed to a greater extent than heart rate and mean arterial pressure (MAP), which are recognised to be unreliable indicators of blood loss; (2) if changes in stroke distance reflected changes in stroke volume derived from thermodilution cardiac output measurements. METHODS: Eight anaesthetised swine had baseline measurements of heart rate, MAP, stroke volume, and stroke distance and were then exsanguinated at a rate of 1 ml/kg/min. Percentage changes from baseline of heart rate, MAP, stroke volume, and stroke distance were compared after 10, 20, and 30 ml/kg blood loss. The animal's blood was then reinfused at the rate of 2 ml/kg/min for 15 min, followed by normal saline 1 ml/kg/min. Percentage changes from baseline measurement of stroke volume and stroke distance over the whole experiment were evaluated by regression analysis. RESULTS: Heart rate, MAP, and stroke distance changed +7.9%, -22.5%, and -18.1% respectively (from baseline values) after 10 ml/kg blood loss; +23.2%, -44.0%, and -47.4% after 20 ml/kg blood loss; and +55.7%, -62.0%, and -69.8% after 30 ml/kg blood loss. Regression analysis of percentage changes in stroke volume and stroke distance from their baseline values at experimental time zero is stroke volume = 1.014 x stroke distance -2.156, r = 0.92, n = 54, P < 0.0001. CONCLUSIONS: (1) At maximal blood loss, stroke distance changes to a greater extent than heart rate and MAP. (2) Changes in stroke distance reflected changes in stroke volume but with less variability at lower values. Stroke distance may be a more useful measure of blood loss than heart rate and MAP.

Animals↗
PubMed1997

Diagnostic distance of high grade prostatic intraepithelial neoplasia from normal prostate and adenocarcinoma.

OBJECTIVE: To develop a distance measure based methodology to support the morphological evaluation of high grade prostatic intraepithelial neoplasia (PIN), a direct precursor of prostate cancer. METHODS: Eight morphological and cellular features were analysed in 20 cases of high grade PIN found in radical prostatectomy specimens from patients with adenocarcinoma. The diagnostic distance was evaluated to measure the extent to which the feature outcomes of the individual high grade PIN cases differed from the expected outcome profile of normal prostate, low and high grade PIN, and cribriform and large acinar adenocarcinoma. The belief value for high grade PIN was evaluated with a Bayesian belief network (BBN). RESULTS: Complete separation existed between the cumulative absolute diagnostic distances of these 20 cases from the prototype feature outcomes of high grade PIN and normal prostate the values for which were < or = 3 (range 0 to 3) and > or = 9 (range 9 to 15), respectively. The distances from low grade PIN (range 3 to 9), cribriform adenocarcinoma (range 2 to 8), and large acinar adenocarcinoma (range 5 to 10) were intermediate and showed overlap in their distribution. When taking into consideration whether the severity of feature changes was increasing or decreasing in comparison with the category prototype outcomes, the cumulative directional diagnostic distances from high grade PIN ranged from -3 to +3. Positive distance values were seen relative to low grade PIN (range +3 to +9) and relative to normal prostate (range +9 to +15). Negative values were found relative to cribriform adenocarcinoma (range -8 to +2). The distance values from large acinar adenocarcinoma ranged from -2 to +4 and partly overlapped with those from the high grade PIN category. A bivariate scattergram derived from both diagnostic distance measures showed excellent separation between the groups' distances. BBN analysis confirmed the morphology based diagnosis. The distance evaluation resulted in 18 cases whose belief value for high grade PIN ranged from 0.60 to 0.87. In the remaining two cases the results of the BBN analysis showed a belief value of 0.50 and 0.57 for low grade PIN and of 0.49 and 0.38 for high grade PIN, respectively. CONCLUSIONS: Distance measure based methodology represents a useful diagnostic decision support tool for the accurate evaluation of high grade PIN.

Adenocarcinoma↗
PubMed1994

Proprioceptive coordination of movement sequences: discrimination of joint angle versus angular distance.

1. The purpose of these experiments was to determine the accuracy with which human subjects could discriminate proprioceptive (nonretinotopic) targets during movement. The targets were located at either a specified angle in joint space, or a specified angular distance from an initial joint angle. 2. In these experiments the right elbows of normal human subjects were passively extended from either predictable or unpredictable starting angles. The subjects were instructed to open the right hand to indicate that the elbow was passing through a target joint angle or a target angular distance. The subjects were not given visual information about the location of the elbow, so they had to rely on proprioceptive input to perform this task. The target (criterion joint angle or angular distance) was learned by the use of proprioception during 8-15 practice trials. 3. Four experiments were conducted. In three experiments the target was located at a constant joint angle, and in the fourth experiment the target was located at a constant angular distance from the starting angle. The starting angle in all four experiments was pseudorandomly varied from trial to trial. 4. On the basis of an analysis of constant errors, subjects were more accurate at discriminating angular distance than joint angle. The slope of the relationship between the starting position and the constant errors was dictated by the task requirement. 5. In the distance discrimination experiment, when the starting angle was more flexed than the intermediate (i.e., central) position, the subjects slightly overshot the target distance. Conversely, when the starting angle was more extended than the intermediate position, the subjects slightly undershot the target distance. 6. In the joint angle discrimination experiments, the opposite results were obtained. Subjects overshot the target when the starting position of the elbow was more extended than the intermediate starting position, and they undershot the target when the starting position was more flexed than the intermediate starting position. The amplitude of these systematic errors increased when the subjects were unaware that the initial angle of their elbow was variable. 7. It is concluded that, in kinesthetic tasks of this type, the discrimination of angular distance is more accurate than the discrimination of joint angle. We hypothesize that the nervous system extracts kinematic information related to both joint angle and angular distance from proprioceptors, and that the encoding and or decoding of angular distance is more accurate than that of absolute joint angle.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1996

Practical equations to predict claudication pain distances from a graded treadmill test.

Treadmill testing is used to estimate the severity of claudication, but routine use is not practical or cost-effective in all settings. Thus, the purposes of this study were: (1) to develop and cross-validate prediction equations for treadmill claudication pain distances in a heterogeneous cohort of peripheral arterial occlusive disease patients, and (2) to determine if the regression equations were more accurate in assessing claudication distances than self-reported distances of patients. Medical history, vital signs, resting ankle/brachial systolic pressure index (ABI), and claudication distances during a graded treadmill test were obtained on a validation group of 178 claudicants and on a cross-validation group of 94 claudicants. The independent predictors of claudication pain distances of the validation group were ABI, body mass index, gender, and current smoking status, with multiple correlation coefficients of R = 0.73 and R = 0.82 for the distances to onset and to maximal pain, respectively. These equations were successfully cross-validated on an independent group of claudicants, as the predicted distances to onset of claudication pain (167.2 +/- 102.6 m) and to maximal pain (354.6 +/- 154.3 m) were similar (p = 0.99) to measured distances (169.1 +/- 127.8 m and 356.6 +/- 181.0 m, respectively). However, the self-reported distances to onset (89.5 +/- 126.3) and to maximal claudication pain (189.2 +/- 284.3) were 1-2 blocks less than either the measured or predicted distances (p < 0.01). It is concluded that claudication pain distances during an incremental treadmill test can be more accurately estimated from a composite of variables obtained during medical screening than by relying on the self-report of patients. Consequently, in clinical settings where treadmill testing is impractical, the functional severity of claudication can be assessed without exercise testing.

Aged↗
PubMedDate not supplied

Normal values of medial and lateral canthal distances in 3 to 18 year-old Nigerians.

BACKGROUND: This study was carried out on male and female Nigerians whose age ranged from 3 to 18 years in order to provide a database of canthal measurements for a predominantly black population and compare them with Caucasians. STUDY DESIGN: All the healthy pupils and students were randomly selected. The ages of the children, adolescents and young adults were approximated to their nearest birthdays. Two different researchers measured each parameter and the mean values were recorded. SETTING: Nursery, primary, secondary schools and the University of Benin, in Benin City, Nigeria. RESULTS: Four hundred and sixty eight males (53.4%) and 408 (46.6%) females making up a total of 876 subjects were studied. The mean values for medial canthal distance for male Nigerians are slightly higher than those established for male Caucasians and these differences are significant (p>0.05). There was no significant difference in the lateral canthal distance between the two groups (p<0.05). Nigerian and Caucasian females have significant difference (p>0.05) in mean values for medial canthal distances but not in lateral canthal distance (p<0.05). The difference in these distances between Nigerian males and females are not significant. Weight and lateral canthal distance showed a covariance of 6.980 while age and lateral canthal distance, age and medial canthal distance showed a covariance of 2.970 and 1.140 respectively. There was no correlation between age, height, weight and the distances measured. CONCLUSION: Medial canthal distances between male and female Nigerians compared to males and female Caucasians show significant variations but not in the lateral canthal distances.

Adolescent↗
PubMed2000

BVAT distance vs. near stereopsis screening of strabismus, strabismic amblyopia and refractive amblyopia; a prospective study of 68 patients.

PURPOSE: Although there have been studies in the past of the difference between distance and near stereopsis in intermittent exotropia, no such comparisons have been studied and/or reported for other forms of strabismus, nor for strabismic functional amblyopia, or for refractive functional amblyopia. METHODS: The study was prospective: Sixty-eight consecutive patients, ages 6-76 years, with either childhood onset strabismus and no amblyopia, childhood onset strabismus and amblyopia, or refractive amblyopia and no strabismus, had their stereopsis measured. Distance stereopsis was determined on the Mentor BVAT with Random Dot E Test (global stereopsis) and the Circle Test (contour stereopsis). Near stereopsis was determined with the Circle Test of the Randot Stereotest. The data were tabulated and analyzed statistically. RESULTS: Of the 26 strabismus/no amblyopia cases, 14 (54%) appreciated distance stereopsis. Of these, 12/14 were intermittent, and other 2 who were constant had deviations of 8 PD or less. Only 4 of the 14 appreciated global stereopsis at distance (mean = 90 sec. of arc), but all 14 appreciated contour stereopsis at distance (mean = 125 sec. of arc). Of all 26, 21 (81%) had near stereopsis (mean = 137 sec. of arc). For the 21 strabismic amblyopes, only one appreciated global stereopsis at distance (120 sec of arc), and 2 (10%) contour stereopsis at distance (mean = 210 sec. of arc). These two and 4 others (total 29%) had near stereopsis (mean = 162 sec. of arc). For the 21 refractive amblyopes, 3 appreciated global stereopsis at distance (mean = 220 sec. of arc), 11 in all, (52%) contour stereopsis at distance (mean = 121 sec. of arc) and 20 (95%) had near stereopsis (mean = 78 sec. of arc). The percentages of patients in all categories capable of appreciating distance stereopsis were "statistically significantly" (P<.05) or clinically/medically significantly different from (less than) the percentages having near stereopsis. CONCLUSIONS: distance stereopsis is more likely to be reduced or absent than near stereopsis in strabismus, strabismic amblyopia and refractive amblyopia and thus appears to be more sensitive to, and better screening for, binocular vision disorders and a stronger and better outcome standard for treatment of binocular vision disorders than near stereopsis.

Adolescent↗
PubMed1990

Analysis of prehistoric biological variation under a model of isolation by geographic and temporal distance.

Biological distances calculated between archeologically recovered human skeletal collections are often used to assess the effects of temporal and spatial distance on subpopulation divergence. Although there are many previous empirical studies that examine skeletal material arrayed across time and/or space, the theoretical expectations for temporally or spatially related variation in biological characteristics have not been formally developed. In this paper I present the infinite island model, the unidimensional stepping-stone model, and the migration matrix method in forms that allow prediction of the genetic distance between groups separated by a given spatial and temporal lag. These models demonstrate that, if there is isolation by geographic distance, then the correlation between genetic and spatial distance (controlling for temporal distance) should be positive and the correlation between genetic and temporal distance (controlling for spatial distance) should be negative. I use observations of nonmetric traits in a sample of prehistoric crania from west-central Illinois to demonstrate the expected relationships among biological, temporal, and spatial distance. The results indicate that, once the effects of temporal trend are removed, biological and spatial distance are positively correlated and biological and temporal distance negatively correlated within this sample.

Cephalometry↗
PubMed1998

Contribution of vestibular nerve irregular afferents to viewing distance-related changes in the vestibulo-ocular reflex.

The contribution of irregular vestibular afferents to viewing distance-related changes in the angular vestibulo-ocular reflex (AVOR) and combined angular and linear VOR (CVOR) was studied in squirrel monkeys trained to fixate earth-stationary targets that were near (10 cm) and distant (90-170 cm) from their eyes. Perilymphatic anodal galvanic currents were used to reversibly silence irregular vestibular afferents for periods of 4-5 s during the AVOR and CVOR evoked by 0.5- to 4-Hz sinusoidal rotations (6-20 degrees/s peak velocity) or 250-400 degrees/s2 acceleration steps. The direction and magnitude of linear translation were changed by positioning the monkeys at different distances off the axis of turntable rotation. The effects of irregular afferent galvanic ablation (GA) on viewing distance-related changes in the AVOR were studied in four animals. Viewing distance-related changes in the AVOR could not always be evoked and were frequently small in amplitude. GA reduced viewing distance-related change in the AVOR by an average of 64% when it was present. Thus vestibular irregular afferents appear to play an important and necessary role in viewing distance-related changes in the AVOR - on those occasions when the changes occur. Viewing distance-related changes in the CVOR were large and reliably evoked. GA had very little effect on the gain or phase of viewing distance-related changes in the CVOR, although the viewing distance-related CVOR responses of individual central vestibular neurons were affected. We conclude that irregular afferents probably contribute to central signal processing related to both the AVOR and the CVOR, but the signals carried by these afferents are only essential for viewing distance-related changes in AVOR.

Animals↗