SEARCH · PubMed Health

Results for “Biometry”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 721 records · Page 40Linked to original sources

PubMed2000

Diagnosis of small-for-gestational-age fetuses between 24 and 32 weeks, based on standard sonographic measurements.

OBJECTIVE: To create and validate a formula using sonographic biometry measurements for the optimal diagnosis of small-for-gestational-age (SGA) fetuses between 24 and 32 weeks of gestation. METHODS: A logistic model using gestational age, femur diaphysis length, abdominal and head circumferences to diagnose SGA was set up in a first group of 64 fetuses born between 24 and 32 weeks (group I). A Receiver Operating Characteristic (ROC) curve was drawn. Our model was compared with standard single ultrasound measurements or combined into an estimated fetal weight (EFW) formula. An external validation was carried out on a second group of 183 fetuses (group II) from another maternity unit (ROC curve and comparisons). RESULTS: The area under the ROC curve was 0.91 in group I and 0.93 in group II. Using a 0.5 cut off point for our model yielded a sensitivity of 76% and specificity of 91% for group I. This model is more specific than most other measurement methods with a similar sensitivity. Using the same cut off point (0.5) in Group II, our model was more specific (98%) but less sensitive (66%) when compared with single ultrasound measurements and EFW formulae. By varying the cut off point, we were able to demonstrate that, for a similar sensitivity, our model had a higher specificity than single ultrasound measurements and had similar specificity to EFW formulae. CONCLUSION: The logistic model we set up was able to calculate an SGA risk score between 24 and 32 weeks of gestation in a population at high risk for elective delivery. The cut off point with a view to diagnosis can vary and makes it possible to give greater importance to the sensitivity or specificity depending on the clinical context.

Abdomen↗

PubMed1999

An appraisal of the disc-macula distance to disc diameter ratio in the assessment of optic disc size.

The disc-macula distance to disc diameter ratio (DM:DD ratio) has been advocated as a method of supporting the diagnosis of optic nerve hypoplasia. A DM:DD ratio of 3.00 has been claimed to be a satisfactory threshold value for this purpose. This study has critically evaluated the above claim and found a value of 3.00 to be too low. The threshold DM:DD ratio values for the diagnosis of unequivocal ONH for an adult population, 5 and 2 years of age were found to be respectively 4.20, 3.93 and 3.70, the values for the diagnosis of mild ONH being 3.68, 3.44 and 3.23. Lower computed values reduce the predictive power. The method of computation of the DM:DD ratio was modified to abolish potential error due to disc rotation and foveal displacement. In an adult population, there was no correlation between the DM:DD ratio and amblyopia or disc ovalness. There was a trend of increasing DM:DD ratio towards myopia and decreasing DM:DD ratio towards hypermetropia; the DM:DD ratio may therefore be falsely high in high myopia. DM:DD ratio values below threshold should therefore be interpreted with care until formal optic disc biometry can be performed.

Adolescent↗

PubMed2002

A multiple regression approach to study optical components of myopia in Singapore school children.

PURPOSE: Previous studies on the optical components of childhood myopia adjusted only for age and gender or reported only the change of individual components with time. We perform a study to assess the association of the optical components of the eye contributing to the degree of myopia by building a statistical model which can better assess the individual effects of each optical component. METHODS: Children 6-12 years old with myopia of -1 to -6 D were used in this study. Autokeratometry was performed to determine the mean corneal power in two perpendicular meridia. Ultrasonography was used to determine the vitreous chamber depth (VCD). Ultrasonography and Scheimflug biometry were used to determine lens thickness (LT) and anterior chamber depth. A stepwise multiple linear regression was used to determine statistically significant independent variables that explain the variation in the mean spherical equivalent of the left eye. The independent variables investigated were anterior chamber length, LT, VCD, mean corneal power, age and gender. The first regression model used measurements of anterior chamber depth and LT from ultrasonography, while the second model used measurements from Scheimflug photography. Statistical significance was set at p < 0.05. RESULTS: Both statistical models have the same significant independent variables - VCD, LT and gender, with similar estimates. In both models, VCD was found to have the strongest partial association with mean spherical equivalent, followed by gender and LT. A more myopic refractive error was associated with (1) a longer eye, (2) an increased LT, and (3) female gender. CONCLUSIONS: Myopia was associated with a longer vitreous chamber. This remained the primary determinant of myopia in Chinese children after consideration of other optical components. The effect of gender and LT on myopia requires further study. These results are in agreement with multiple regression analyses in Singapore adults.

Anterior Chamber↗

PubMed2005

[Smoking as potential confounder in german epidemiological studies: standardization of assessment, quantification, and analysis].

Tobacco smoking is one of the most frequently examined risk factors in epidemiological studies due to the high frequency of smoking in the population and its high risk potential. This paper discusses the issue of standardization of the assessment of tobacco exposure in German epidemiological studies based on a suggestion of the working group "Epidemiological methods" of the German Society of Epidemiology (DGEpi), the German Society of Social Medicine and Prevention (DGSMP), and German Society of Medical Informatics, Biometry and Epidemiology (GMDS) together with the working group "Epidemiology in the workplace" of the DGEpi and the German Society of Occupational and Environmental Medicine (DGAUM). The main element is a short questionnaire for German adults for the assessment of tobacco smoking in epidemiological studies where smoking is a potential confounder. In addition, information on the consideration of intermittent periods of non-smoking, a very short questionnaire for medical examinations in the workplace or non-responder interviews as well as the quantification and statistical modelling of smoking are presented. A brief discussion of scientific problems and questionnaires related to the exposure to environmental tobacco smoke is given.

Bias↗

PubMed2000

Ultrasonographic ear length measurement in normal second- and third-trimester fetuses.

OBJECTIVE: We sought to develop a nomogram for fetal ear length measurements from a large population of healthy second- and third-trimester fetuses and to investigate the correlation of fetal ear length with other standard fetal biometry measurements, as follows: biparietal diameter, head circumference, abdominal circumference, femur length, and humerus length. STUDY DESIGN: Ear length measurement was obtained prospectively in 4240 singleton fetuses between 15 and 40 weeks' gestational age. Either complete data for normal karyotype on amniocentesis or normal infant examination at birth or both were available in 2583 cases. These constituted the final study population. RESULTS: A nomogram was developed by linearly regressing ear length on gestational age (Ear length [in millimeters] = 1.076 x Gestational age [in weeks] - 7. 308). There was a high correlation between ear length and gestational age (r = 0.96; P =.0001). CONCLUSION: The results of this study provide normative data on growth of fetal ear length from 15 to 40 weeks' gestation. Good correlation was also observed between ear length and other fetal biometric measurements (biparietal diameter, head circumference, abdominal circumference, femur length, and humerus length).

Amniocentesis↗

PubMed2003

Down syndrome screening using race-specific femur length.

OBJECTIVE: The study was undertaken to evaluate the influence of maternal race on fetal femur length when screening for Down syndrome. STUDY DESIGN: We reviewed our patient databases to obtain fetal biometry from 15 to 22 weeks' gestation, maternal race, and cases of Down syndrome. Institution and race-specific regression lines for femur length (FL) to biparietal diameter (BPD) were created. The efficiency of using published expected FL was compared with our institution and race-specific regression in screening for Down syndrome. RESULTS: There were 4350 African American, 4271 white, 2315 Hispanic, and 654 Asian subjects and 42 cases of Down syndrome (1:276) included in the study. Our institutionally derived regression for FL by BPD had an R(2) of 0.82. Regression lines for FL by BPD generated by race had an R(2) of 0.86, 0.84, 0.83, and 0.80 for African American, Hispanic, Asian, and white subjects, respectively. The race-specific regression was no better than institution-specific data. CONCLUSION: Using institution-specific FL was more efficient in screening for Down syndrome than published expected FL; race-specific analysis did not improve efficiency.

Asian People↗

PubMed1998

Karl Pearson's mathematization of inheritance: from ancestral heredity to Mendelian genetics (1895-1909).

Long-standing claims have been made for nearly the entire twentieth century that the biometrician, Karl Pearson, and colleague, W. F. R. Weldon, rejected Mendelism as a theory of inheritance. It is shown that at the end of the nineteenth century Pearson considered various theories of inheritance (including Francis Galton's law of ancestral heredity for characters underpinned by continuous variation), and by 1904 he 'accepted the fundamental idea of Mendel' as a theory of inheritance for discontinuous variation. Moreover, in 1909, he suggested a synthesis of biometry and Mendelism. Despite the many attempts made by a number of geneticists (including R. A. Fisher in 1936) to use Pearson's chi-square (X2, P) goodness-of-fit test on Mendel's data, which produced results that were 'too good to be true', Weldon reached the same conclusion in 1902, but his results were never acknowledged. The geneticist and arch-rival of the biometricians, Williams Bateson, was instead exceptionally critical of this work and interpreted this as Weldon's rejection of Mendelism. Whilst scholarship on Mendel, by historians of science in the last 18 years, has led to a balanced perspective of Mendel, it is suggested that a better balanced and more rounded view of the hereditarian-statistical work of Pearson, Weldon, and the biometricians is long overdue.

Biometry↗

PubMed1996

Age-related changes in the accommodation mechanism.

Presbyopia is caused by changes in the visco-elastic properties of the lens or the choroid or both. Far-to-near (FN) accommodation dynamics are dominated by the properties of the lens, whereas near-to-far (NF) accommodation dynamics depend on the properties of the lens as well as the choroid. The aim of this study was to gain more insight into the cause of presbyopia by analyzing how FN and NF accommodation dynamics change as a function of age. Changes in axial lens thickness during accommodation were measured in vivo using continuous ultrasonographic biometry. The measurements were analyzed with the use of a biomechanical model of the mechanism of accommodation. Fitting the model to the responses yields time constants of FN and NF accommodation. The time constants FN and NF increase with age at an approximately equal rate: 7 ms/year (+/- 1.8 SEM) and 6 ms/year (+/- 1.6 SEM), respectively. This result supports a lenticular cause of presbyopia. In addition, estimations of the lens damping coefficients at different ages are given for the first time: the damping coefficient of the lens increases 20-fold between 15 and 55 years of age.

Accommodation, Ocular↗

PubMed2006

High maternal and fetal plasma urocortin levels in pregnancies complicated by hypertension.

OBJECTIVE: We evaluated maternal and fetal plasma levels and placental mRNA expression of urocortin, a placental vasoactive neuropeptide, in singleton pregnancies (n = 70) complicated by hypertensive disorders classified as gestational hypertension (n = 36), pre-eclampsia (n = 19), and pre-eclampsia complicated by intrauterine growth restriction (PE/IUGR, n = 15), and in 70 healthy normotensive singleton pregnancies. METHODS: Plasma levels were assayed by radioimmunoassay, fetal biometry by ultrasound scans, utero-placental and fetal perfusion by Doppler velocimetry, and placental urocortin mRNA expression by quantitative real time reverse transcriptase-polymerase chain reaction. The main outcome measures were the correlation of urocortin concentrations with patterns of the utero-placental and fetal circulation, and the early prediction of a poor neonatal outcome such as the occurrence of perinatal death and intraventricular hemorrhage. RESULTS: Maternal and fetal urocortin levels were significantly (both P < 0.001) higher in gestational hypertension, pre-eclampsia and PE/IUGR women than in controls, and correlated with Doppler velocimetry patterns. Fetal concentrations were significantly (P < 0.0001) higher than and significantly (P < 0.0001) correlated to maternal levels. Placental mRNA expression did not change. Ten out of 140 newborns had a poor neonatal outcome, with an overall prevalence of 7.14% (pretest probability). Using the receiver operator characteristics curve analysis cut-off values, the probability of a poor neonatal outcome was 66.7% when urocortin was used, and was 0% if levels were unaltered. CONCLUSIONS: Maternal and fetal urocortin levels are increased in hypertensive disorders of pregnancy. Since urocortin has vasoactive properties, the evidence of increased urocortin levels in hypertensive disorders may represent an adaptive fetal response.

Adult↗

PubMed2006

Development of a fully automated peripheral anterior chamber depth analyzer and evaluation of its accuracy.

PURPOSE: The aim of this study was to improve the scanning peripheral anterior chamber depth analyzer (SPAC) for measuring anterior chamber depth (ACD), differentiating eyes with shallow anterior chamber, and automatically categorizing eyes into subgroups based on the ACD values. We also investigated its accuracy for measuring anterior ocular biometry. MATERIALS AND METHODS: The improved SPAC system was equipped with an auto-focusing system for measuring ACD from the optical axis to the limbus without contacting the ocular surface, in addition to an auto-measuring system for determining central corneal thickness (CCT) and corneal radius of curvature (CRC). This system was also equipped with an auto-diagnosing program for differentiating eyes with narrow angle and an auto-classifying program for categorizing eyes into 12 subgroups according to the ACD values. A dummy eye was used for investigating the measurement accuracy and reproducibility of CCT, CRC, and ACD. Measurement duration and clinical availability were investigated using healthy subjects and glaucoma patients. RESULTS: The SPAC-measured CCT, CRC, and ACD values were very similar to the theoretical values obtained from the dummy eye and their coefficients of variation were less than 1%. This system completed ACD measurement in 15.6+/-1.0 seconds and the mean coefficient of variation of ACD was 8.8+/-2.3%. The improved SPAC system successfully differentiated eyes with narrow angle from those with wide open angle. CONCLUSIONS: The improved SPAC system can measure ACD easily with good accuracy and reproducibility, and is considered to be suitable for evaluating ACD in routine examinations and screening eyes with narrow angle.

Adult↗

PubMed2005

Refractive and biometric changes with silicone hydrogel contact lenses.

PURPOSE: This study reports data from an 18-month longitudinal study of neophyte contact lens wearers and compares changes in ocular refraction and biometry induced by daily wear and continuous wear of two different silicone hydrogel (SiH) materials. METHODS: Forty-five subjects were enrolled in the study and randomly assigned to wear one of the two silicone hydrogel materials: Lotrafilcon A or Balafilcon A lenses on either a daily or continuous wear basis. Measurements of objective refraction, axial length, anterior chamber depth, corneal curvature, and the rate of peripheral corneal flattening were performed before and 1, 3, 6, 12, and 18 months after initial fitting. RESULTS: Mean spherical equivalent refractive error increased in the myopic direction in all contact lens groups across time (p < 0.001). Axial length was the main biometric contributor to the development of myopia. After 18 months of lens wear, subjects in the Lotrafilcon A group showed the greater mean increase in myopia (i.e., -0.50 D). CONCLUSIONS: The results of this study show that increases in myopia, similar if not higher than those found to occur normally in young adult noncontact lens wearers, still occur with silicone hydrogel contact lens wear. The main biometric contributor to the progression of myopia was an increase in axial length. Differences between our results and those of previous studies with silicone hydrogel contact lenses could be attributed to the differing populations used in which both age and occupation may have played a role.

Adult↗

PubMed2005

Anatomical study of the proximal femur in the fetus.

Two angles effectively describe the upper femur geometry: The neck shaft angle (NSA) and anteversion (AV). AV and NSA decrease from birth until they reach their adult values, but little work has focused on in-utero life. Our aim was to determine if and how AV and NSA change through the fetal life. Eighty-seven femurs from 44 formalin preserved fetuses were sampled to achieve a biometry. Correlation tests and linear regression showed that AV was highly correlated with age: AV increases during the second half of gestation. No conclusion can be given concerning NSA. It is speculated that these changes may be caused by mechanical stresses.

Biometry↗

PubMed2007

Using ultrasonic fetal size measurements to estimate gestational age in Brisbane, Australia.

The purpose of this paper was to construct population-specific charts of gestational age (GA) from antenatal ultrasound biometry assessment using a large sample of normal Australian pregnancies when examination was carried out to a standard protocol by experienced operators. All consenting eligible women attending a large Brisbane clinic between January 1993 and April 2003 with GA between 15 and 41 weeks, determined before examination from the last menstrual period date and concordant with the biometric-derived gestation published within the Australian Society for Ultrasound in Medicine (ASUM) policies and statements, were recruited into the prospective study if fulfilling the inclusion criteria. Biparietal diameter, femur length, abdominal circumference and head circumference measurements were recorded using ASUM standard protocol for mid and third trimester obstetric morphology scans. Statistical analyses were carried out using polynomial regression models and thorough diagnostic checks were undertaken. Included within the study were separate scans for 20,555 pregnancies from 17,660 women. Equations, means and 95% reference intervals for GA were derived for each sonographic measurement. These new population-specific regression equations complement those previously published in the same sample of Australian pregnancies. Once validated, we believe they should form the basis of a new Australian standard for ASUM.

Adult↗

PubMed1995

An appraisal of the accuracy of Littmann's method of determining the real dimension of a retinal object.

Estimation of the neuroretinal rim area in absolute units is becoming increasingly desirable in the evaluation of optic discs of glaucoma suspects. There are various methods of optic disc biometry, photogrammetric techniques being the most commonly reported. Any method of estimation of the real dimension of a retinal object must consider magnification due to the patient's eye. Photogrammetric techniques use Littmann's method extensively in this respect, assuming that it is an accurate way of performing the necessary correction. The accuracy of Littmann's method has not yet been assessed in a physiological setting. This study has found that, when the normal distributions of the optical elements eye are considered, in estimating the neuroretinal rim area, the method is at least 86% accurate (95% confidence interval) within an ametropia range -4 to +4 dioptres. This level of accuracy should be considered when drawing conclusions from any study in which Littmann's method is used.

Algorithms↗

PubMed2005

The impact of cataract severity on measurement acquisition with the IOLMaster.

PURPOSE: The Zeiss IOLMaster optical biometry system provides superior prediction of refractive outcome of cataract surgery compared to applanation ultrasound. However, measurement is not always possible in the presence of dense cataract. The purpose of this study was to elucidate the rate of measurement acquisition failure due to cataract and how this varies with morphology and severity. METHODS: A total of 149 subjects were prospectively enrolled and visual acuity, Lens Opacities Classification System III (LOCS III) scores, ultrasonic A-scan and IOLMaster axial lengths were measured. Chi-squared analysis was used to test the null hypothesis that cataract severity has no effect on measurement failure rate. RESULTS: Measurements could not be obtained with the IOLMaster in nine cases for reasons other than cataract. Cataract caused measurement acquisition failure in 22 (15.9%) cases, including all mature cataracts (n=3) and posterior subcapsular cataracts (PSC) with LOCS III (p>3.5; n=18). The null hypothesis was accepted for cortical (chi(2)=2.94, d.f.=2, p>0.05) and nuclear (chi(2)=7.91, d.f.=4, p>0.05) ataract, but rejected for PSC (chi(2)=111, d.f.=3, p<0.001). All cases could be measured with ultrasound. CONCLUSIONS: The IOLMaster fails to acquire axial length measurement in approximately 20% of UK public hospital cataract patients. Failure is principally due to PSC, whereby the LOCS III score of p=3.5 defines the limit of PSC severity that the IOLMaster can measure.

Adult↗

PubMed2005

The effect of parental history of myopia on eye size of pre-school children: a pilot study.

PURPOSE: To evaluate parental history of myopia as a predictor of refractive error and eye size in Chinese pre-school children. METHODS: A total of 514 pre-school children (aged 2.3--6.4 years) were examined. Parental history of myopia, amount of near work performed, refractive status and ocular biometry were recorded. RESULTS: There was no significant difference in spherical equivalent refraction (SER) among children with no myopic parents (mean+0.94+/-0.05 D), one myopic parent (mean+0.77+- 0.07 D) and two myopic parents (mean+0.79+/- 0.12 D) (p=0.102) after controlling for age and amount of near work. Further, children with more myopic parents did not have longer eyeballs (p=0.335). CONCLUSIONS: In this study in Chinese pre-school children, parental history of myopia was not found to be associated with a myopic refractive error or increased eyeball length. Further studies with larger sample sizes would help to confirm these results.

Asian People↗

PubMed2006

Refractive error after triple and non-simultaneous procedures: is the application of a standard constant keratometry value in IOL power calculation advisable?

PURPOSE: The purpose of this investigation was to determine whether or not the use of a standard constant keratometry value in cases of preoperative abnormal keratometry values in biometry for triple procedures is advisable. METHODS: Cataract surgery and penetrating keratoplasty were performed in 82 eyes; 53 eyes underwent triple procedures and 29 eyes underwent non-simultaneous procedures. A standard constant keratometry value of 42.50 D was applied in 18 triple-procedure eyes because the preoperative measured keratometry values were outwith the normal range (41-47 D). The spherical equivalent and expected values were compared after a mean follow-up of 20.5 months. RESULTS: Cases in the triple-procedure group that achieved spherical equivalent within +/- 2.0 D of expected values included nine of 18 eyes (50%) in which a standard constant keratometry value of 42.50 D was applied, three of 17 eyes (18%) in which keratometry values outwith the normal range were applied (p = 0.044), and eight of 18 eyes (45%) in which keratometry values within the normal range were applied (p = 0.862). Cases in the non-simultaneous procedure group that achieved spherical equivalent within +/- 2.0 D of expected values included 22 of 24 eyes (92%) in which keratometry values within the normal range were applied (p = 0.0025), and five of five eyes (100%) in which a standard constant keratometry value was applied. CONCLUSIONS: The application of a standard constant keratometry value of 42.50 D for intraocular lens power calculation in triple procedures can be recommended if abnormal keratometry values were measured previously. If possible, non-simultaneous procedures should take priority.

Biometry↗

PubMedDate not supplied

Agreement between A-mode and B-mode ultrasonography in the measurement of ocular distances.

It is generally accepted that A-mode ultrasonography is more accurate than B-mode in measuring intraocular dimensions. Consequently, A-mode ultrasonography is the procedure of choice in ocular biometry while B-mode ultrasonography is used principally for diagnostic purposes. In this study, we investigated the agreement between measurement of intraocular distances using A- and B-mode ultrasonography on freshly enucleated camel eyes. Our results suggest that relative to average A-mode values, B-mode overestimates corneal thickness (bias = 0.06 mm) and anterior chamber depth (bias = 0.03 mm), while it underestimates lens thickness (bias = -0.11 mm), vitreous chamber depth (bias = -0.32 mm) and axial length (bias = -0.40 mm). In general, difference between A- and B-mode values is larger for deeper intraocular dimensions. This implies that the two methods are more likely to give different readings for measurements of lens thickness, vitreous chamber depth and axial length.

Animals↗