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At least 19 recordsLinked to original sources
PubMed2000

Outer orbital distance, inner canthal distance and interpupillary distance, proptosis in children with homozygous sickle cell disease.

BACKGROUND: On basis of clinical observation paediatricians in Kinshasa had the impression that children with homozygous sickle cell disease have a special face characterised by hypertelorism. OBJECTIVE: The purpose of the study is to determine outer orbital, inner canthal and interpupillary distances as well as proptosis in children with sickle cell disease. METHODS: These measurements were performed on 66 Congolese children with homozygous sickle cell disease, aged from 2 to 18 years. The measurements were performed with the Hertel exophthalmometer for the proptosis and the outer orbital distance, with the pupillometer model PD-2 meter for the interpupillary distance and with a ruler for the inner canthal distance. The results were compared with those of 95 healthy children of similar age. RESULTS: All measurements were age related. In every age group the values for inner canthal distance were identical to those of healthy children, but the interpupillary, the outer orbital distances and the proptosis were significantly smaller. CONCLUSIONS: A slow growth of orbital tissue in children with homozygous sickle cell was suggested to explain the difference with healthy children. Other biometric studies comparing the orbital measurements with the rest of the body are needed to confirm or refute this hypothesis.

Adolescent↗
PubMed1977

Effect of distance information and range on two indices of visually perceived distance.

Subjects made verbal reports of the perceived distance of near visual targets and indicated their distances by pointing at them with an unseen hand. The targets were presented under three stimulus conditions: monocular, binocular, and multicue. Two ranges of target distance were studied in separate experiments: 11-39 cm and 21-33 cm. When reciprocals of both response distance and target distance were plotted, all functions were approximately linear. The verbal and manual responses (distance indices) differed greatly, but were found to be related by a constant transform. The range of target distances had no effect on either index. The standard deviation of the manual response was about half that of the verbal response. Stimulus condition had a large effect, with the multicue condition producing the greatest change in indicated distance. and the monocular condition the least. The results are discussed with reference to the definition of perceived distance, and hypothesis concerning the integration of distance information.

Adult↗
PubMedDate not supplied

Normal values of inner canthal distance, interpupillary distance and palpebral fissure length in normal Chinese children in Taiwan.

Ocular measurements, including inner canthal distance, outer canthal distance, interpupillary distance, and palpebral fissure length are important in the evaluation of congenital deformities and posttraumatic telecanthus. In this research, 4446 normal Chinese children in Taiwan were enrolled in our study. The sample of 284 full term neonates, 2742 infants and children aged from 1 month to 3 years, and 1420 preschool children were measured for inner canthal distance, outer canthal distance, interpupillary distance and palpebral fissure length. We calculated the mean value and standard deviation of the ocular measurements in normal Chinese newborns, infants and preschool children in Taiwan under 5 years. No significant sex differences were observed. Compared with previous studies, inner canthal distance, outer canthal distance and interpupillary distance in Chinese children in Taiwan were wider than those in Caucasian children, but the palpebral fissure length was not significantly different. We also found that inner canthal distance was wider than palpebral fissure length at the same age; therefore it was not correct to diagnose hypertelorism in Chinese children in Taiwan; as if an imaginary third eye could fit between the eyes. Thus, we suggest that measurements should be adjusted with normal standards specific for race. Consideration of the position of eyes is relevant for the diagnosis of a large number of syndromes.

Child, Preschool↗
PubMed1982

Scales for subjective distance in a large open field from the fractionation method: effects of type of judgment and distance range.

By means of the method of fractionation, scales for subjective distance were derived from five different types of judgment accomplished with two ranges of distance estimated in a large open field. It was found (a) that the scales for subjective distance are to a considerable extent influenced by ways of obtaining the judgments, (b) that the scales are relatively uninfluenced by range of distance, (c) that the exponents of the scales for egocentric distances are different from those for exocentric distances, (d) that the functions for egocentric distances are slightly decelerated but for exocentric distances slightly accelerated, and (e) that the average exponent for all subjects was 0.98.

Adolescent↗
PubMed1991

Effects of limited input distance constraints upon the distance geometry algorithm.

In this paper we examine the distance geometry (DG) algorithm in the form used to determine the structure of proteins. We focus on three aspects of the algorithm: bound smoothing with the triangle inequality, the random selection of distances within the bounds, and the number of distances needed to specify a structure. Computational experiments are performed using simulated and real data for basic pancreatic trypsin inhibitor (BPTI) from nmr and crystallographic measurements. We find that the upper bounds determined by bound smoothing to be a linear function of the true crystal distance. A simple model that describes the results obtained with randomly selected trial distances is proposed. Using this representation of the trial distances, we show that BPTI DG structures are more compact than the true crystal structure. We also show that the DG-generated structures no longer resemble test structures when the number of these interresidue distance constraints is less than the number of degrees of freedom of the protein backbone. While the actual model will be sensitive the way distances are chosen, our conclusions are likely to apply to other versions of the DG algorithm.

Algorithms↗
PubMed1993

End-to-end diffusion coefficients and distance distributions from fluorescence energy transfer measurements: enhanced resolution by using multiple acceptors with different Förster distances.

We measured distance distributions and end-to-end diffusion coefficients of donor-acceptor pairs linked by a flexible methylene chain using frequency-domain fluorescence energy transfer measurements. The donor was an indole group, and two acceptors with different Förster distances were used. The uncertainties in the recovered parameters describing the end-to-end distance distribution and diffusion coefficient were rather large when each donor-acceptor pair was analyzed separately. It was not possible to resolve distance distributions in the presence of intra-molecular diffusion when the Förster distance was comparable to the mean and half-width of the distribution. Global analysis using two acceptors dramatically improved the resolution. Surprisingly, the Förster distances need not be very different, and a 20% difference between the two R0 values resulted in substantial improvements in resolution. Both the simulations and the experiments suggest the benefit of using global analysis with different Förster distances to obtain reliable distance distribution parameters in the presence of diffusion.

Benzenesulfonates↗
PubMed1985

Binocular distance perception: egocentric distance tasks.

This study extends and tests a theory of binocular distance perception that has been shown to give a good account of performance in relative distance tasks. Here the theory is tested in two experiments in which the observer directly indicates perceived egocentric distance of targets (perceived distance from himself or herself) by means of a verbal report or manual pointing response. In the first, the distance to two targets is varied while maintaining a constant disparity between them. In the second, one target is held fixed while the distance to a second target is varied. In each case, the observer indicates the perceived distance of each target. Manual and verbal responses are found to agree with each other to within a linear transform. Both sets of data are shown to be consistent with the theory and are used to estimate the parameters of the theory. There is no other theory that predicts these results.

Adolescent↗
PubMed1998

Distance geometry generates native-like folds for small helical proteins using the consensus distances of predicted protein structures.

For successful ab initio protein structure prediction, a method is needed to identify native-like structures from a set containing both native and non-native protein-like conformations. In this regard, the use of distance geometry has shown promise when accurate inter-residue distances are available. We describe a method by which distance geometry restraints are culled from sets of 500 protein-like conformations for four small helical proteins generated by the method of Simons et al. (1997). A consensus-based approach was applied in which every inter-Calpha distance was measured, and the most frequently occurring distances were used as input restraints for distance geometry. For each protein, a structure with lower coordinate root-mean-square (RMS) error than the mean of the original set was constructed; in three cases the topology of the fold resembled that of the native protein. When the fold sets were filtered for the best scoring conformations with respect to an all-atom knowledge-based scoring function, the remaining subset of 50 structures yielded restraints of higher accuracy. A second round of distance geometry using these restraints resulted in an average coordinate RMS error of 4.38 A.

Computer Simulation↗
PubMed1998

Fixation disparity at different viewing distances and the preferred viewing distance in a laboratory near-vision task.

Previous research has shown that subjects with normal binocular vision differ reliably in the extent to which their fixation disparity changes in the exo direction when the viewing distance is shortened from 100 to 20 cm. Since fixation disparity can lead to asthenopic complaints, the present study investigates whether an exo fixation disparity induced by proximity may cause subjects to move to a longer viewing distance during a near-vision task in order to reduce exo fixation disparity. In two optometric sessions, fixation disparity and accommodation were tested at 60, 40, and 30 cm viewing distance. In a further session, subjects were required to begin a one-hour near-vision task at about 40 cm viewing distance, at which the text characters subtended a comfortable visual angle of 21 min arc. Later, the subjects were free to adopt any viewing distance. In the initial phase of the task, subjects moved back from the screen to a greater or lesser extent that was correlated with the amount of proximal exo fixation disparity: the more a subject's fixation disparity changed to exo when the viewing distance had been shortened from 60 to 30 cm the more he or she moved to longer viewing distances in the course of the near-vision task. Further, the more distant the resting position of vergence (dark vergence), the more visual complaints the subjects indicated after the task relative to before.

Accommodation, Ocular↗
PubMed1991

Distance-constraint approach to higher-order structures of globular proteins with empirically determined distances between amino acid residues.

An analysis of higher-order structures of globular proteins by means of a distance-constraint approach is presented. Conformations are generated for each of 21 test proteins of small and medium sizes by optimizing an objective function f = sigma sigma wij(dij - (dij]2, where dij is a distance between residues i and j in a calculated conformation, (dij) is an assigned distance to the (ij) pair of residues which is determined based on the statistics of known three-dimensional structures of 14 proteins in the earlier study, and wij is a weighting factor. (dij) involves information about hydrophobicity and hydrophilicity of each amino acid residue and about connectivity of a polypeptide chain. In these calculations, only the amino acid sequence is used as input data specific to a calculated protein. With respect to higher-order structures regenerated in the optimized conformations, the following properties are analyzed: (a) N14 of a residue, defined as the number of residues surrounding the residue located within a sphere of radius of 14 A; (b) root-mean-square differences of the global and local conformations from the corresponding X-ray conformations; (c) distance profiles in the short and medium ranges; and (d) distance maps. The effects of supplementary information about locations of secondary structures and disulfide bonds are also examined to discuss the potential ability of this methodology to predict the three-dimensional structures of globular proteins.

Amino Acids↗
PubMed1988

Resolution of end-to-end distance distributions of flexible molecules using quenching-induced variations of the Forster distance for fluorescence energy transfer.

We describe a new method to recover the distribution of donor-to-acceptor (D-A) distances in flexible molecules using steady-state measurements of the efficiency of fluorescence energy transfer. The method depends upon changes in the Forster distance (Ro) induced by collisional quenching of the donor emission. The Ro-dependent transfer efficiencies are analyzed using nonlinear least squares to recover the mean D-A distance and the width of the distribution. The method was developed and tested using three synthetic D-A pairs, in which the chromophores were separated by alkyl chains of varying lengths. As an example application we also recovered the distribution of distances from the single tryptophan residue in troponin I (trp 158) to acceptor-labeled cysteine 133. The half-width of the distribution increases from 12 A in the native state to 53 A when unfolded by guanidine hydrochloride. For both TnI and the three model compounds the distance distributions recovered from the steady-state transfer efficiencies were in excellent agreement with the distributions recovered using the more sophisticated frequency-domain method (Lakowicz, J.R., M.L. Johnson, W. Wiczk, A. Bhat, and R.F. Steiner. 1987. Chem. Phys. Lett. 138:587-593). The method was found to be reliable and should be generally useful for studies of conformational distributions of macromolecules.

Energy Transfer↗
PubMed1984

The distance between S1, S21, and the 3' end of 16S RNA in 30S ribosomal subunits. The effect of poly(uridylic acid) and 50S subunits on these distances.

The apparent distances between probes covalently attached to the cysteine thiols of S1 or S21 and the 3' end of 16S RNA in Escherichia coli 30S ribosomal subunits were determined by non-radiative energy transfer to be: S21-16S RNA, 5.1 nm; S21-S1, 6.9 nm; S1-16S RNA, 6.8 nm. Binding of poly(uridylic acid) to 30S subunits causes the apparent distances between S1 and 16S RNA or S21 and 16S RNA to increase by more than 1.2 nm and 0.5 nm, respectively, but has little or no effect on the S1-S21 distance. Binding of 50S subunits causes an apparent increase in the S21-16S RNA and S21-S1 distances by 1.0 nm and 0.8 nm, respectively, but has little or no effect on the S1-16S-RNA distance.

Coumarins↗
PubMed1978

Genetical distance and dermatoglyphic characters. II. Intrapopulation distance coefficients.

This paper attempts to evaluate the dermatoglyphic (genetical) distance between two Polish population samples in relation to the intrapopulation distance coefficients estimated within each sample. All the coefficients have been based, in turn, on frequencies of fingertip, palmar and sole pattern elements, separately and for all characters combined. The results of a comparison of various combinations of dermatoglyphic characters with one another in respect of all successive values of a distance coefficient indicate that, if populations of mostly related individuals were compared, sole patterns have been the most efficient ones in differentiating between the two normal population samples. The values of inter- and intrapopulation distance coefficients obtained from samples consisting mostly of family units have been compared with those estimated in samples of non-related individuals. The limitations and difficulties in the interpretation of the values of a distance coefficient related both to the material used and statistical procedures are discussed.

Dermatoglyphics↗
PubMed1990

Isolation by distance and correlation analysis of distance measures in the study of population structure: example from the Island of Hvar.

Assessment of the population structure on the island of Hvar is based on the analysis of Malécot's isolation by distance model. We have tested the fit of the model by regression analysis of different measures of similarity (genetic kinship) and distance [Hamming's HSM distance for linguistic data; Mahalanobis's D2 distances for anthropometric head and body dimensions, radiogrammetric dimensions of metacarpal bones, physiological (cardiorespiratory) traits, and quantitative dermatoglyphic properties of the digitopalmar complex; and Edwards's E2 for frequencies of erythrocyte antigens]. Good fit of the model for linguistic and anthropometric data, which was demonstrated in previous studies on other eastern Adriatic populations, is confirmed. We compared parameters of the model with those already published for various populations in the eastern Adriatic and other parts of the world. We also evaluated the pattern of correlations between different measures of geographic, biological, and sociocultural distances through principal components analysis and interpreted the results within the context of microevolutionary theory and the population's ethnohistorical background.

Adult↗
PubMed1998

The necessity of a perception-action approach to definite distance perception: monocular distance perception to guide reaching.

In this investigation of monocular perception of egocentric distance, the authors advocate the necessity of a perception-action approach because calibration is intrinsic to definite distance perception. A helmet-mounted camera and display were used to isolate optic flow generated by participants' head movements toward a target, and participants' reaches to place a stylus either in a target hole (Experiments 1, 2, and 4) or aligned under a target surface (Experiment 3) were analyzed. Conclusions are that binocular distance perception is accurate, monocular distance perception yields compression that is not eliminated by feedback, but feedback is used to eliminate underestimation generated by restriction of the size of the visual field.

Adult↗
PubMed1988

Determination of three-dimensional structures of proteins from interproton distance data by hybrid distance geometry-dynamical simulated annealing calculations.

A new hybrid distance space-real space method for determining three-dimensional structures of proteins on the basis of interproton distance restraints is presented. It involves the following steps: (i) the approximate polypeptide fold is obtained by generating a set of substructures comprising only a small subset of atoms by projection from multi-dimensional distance space into three-dimensional cartesian coordinate space using a procedure known as 'embedding'; (ii) all remaining atoms are then added by best fitting extended amino acids one residue at a time to the substructures; (iii) the resulting structures are used as the starting point for real space dynamical simulated annealing calculations. The latter involve heating the system to a high temperature followed by slow cooling in order to overcome potential barriers along the pathway towards the global minimum region. This is carried out by solving Newton's equations of motion. Unlike conventional restrained molecular dynamics, however, the non-bonded interactions are represented by a simple van der Waals repulsion term. The method is illustrated by calculations on crambin (46 residues) and the globular domain of histone H5 (79 residues). It is shown that the hybrid method is more efficient computationally and samples a larger region of conformational space consistent with the experimental data than full metric matrix distance geometry calculations alone, particularly for large systems.

Histones↗
PubMed1998

Comparison of frequency-distance relationship and Gaussian-diffusion-based methods of compensation for distance-dependent spatial resolution in SPECT imaging.

The goal of this investigation was to compare resolution recovery versus noise level of two methods for compensation of distance-dependent resolution (DDR) in SPECT imaging. The two methods of compensation were restoration filtering based on the frequency-distance relationship (FDR) prior to iterative reconstruction, and modelling DDR in the projector/backprojector pair employed in iterative reconstruction. FDR restoration filtering was computationally faster than modelling the detector response in iterative reconstruction. Using Gaussian diffusion to model the detector response in iterative reconstruction sped up the process by a factor of 2.5 over frequency domain filtering in the projector/backprojector pair. Gaussian diffusion modelling resulted in a better resolution versus noise tradeoff than either FDR restoration filtering or solely modelling attenuation in the projector/backprojector pair of iterative reconstruction. For the pixel size investigated herein (0.317 cm), accounting for DDR in the projector/backprojector pair by Gaussian diffusion, or by applying a blurring function based on the distance from the face of the collimator at each distance, resulted in very similar resolution recovery and slice noise level.

Computer Simulation↗