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Biometry of the posterior lens capsule: a new method to predict pseudophakic anterior chamber depth.
The distance between the anterior corneal vertex and the posterior lens capsule was measured in 60 eyes before and three months after extracapsular cataract extraction with implantation of a posterior chamber lens. The preoperative capsule position ranged from 6.15 mm to 8.60 mm and averaged 7.64 +/- 0.47 mm (+/- SD). All posterior lens capsules had moved anteriorly following surgery. The postoperative capsule position ranged from 4.31 mm to 5.53 mm and averaged 4.93 +/- 0.29 mm. The postoperative capsule position could be predicted by the following optimized multiple linear regression equation: 2.4 + 0.011 x patient age + 0.171 x anterior chamber depth + 0.051 x axial length. The multiple correlation coefficient was 0.48. The postoperative anterior depth could be predicted with a correlation coefficient of 0.61 by subtracting both the averaged value of the clinical "laser space" and the exact central implant thickness from the estimated position of the posterior lens capsule. We suggest that this principle for predicting the postoperative anterior chamber depth may be useful for a number of lenses with different designs.
The statistical frame of mind in systematic biology from quantitative zoology to biometry.
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Inter-observer variation in clinical optic disc biometry.
This study investigated the inter-observer reproducibility of measurements of the optic nerve head as carried out with a clinical optic disc biometer. This instrument employs a modification of indirect ophthalmoscopy to enable measurement of fundus structures. Measurements were made independently by two observers on 84 eyes of 47 patients. The median inter-observer differences for each measurement were as follows: maximum disc diameter, 0.085 mm; minimum disc diameter, 0.080 mm; maximum cup diameter, 0.098 mm; minimum cup diameter, 0.078 mm; disc area, 0.225 mm2; neuroretinal rim area, 0.215 mm2. Utilising the above measurements, the instrument automatically calculates a 'rim index' to take account of variations in disc size. It then interprets the disc as normal, suspicious or glaucomatous. The optic disc biometer produced seriously conflicting interpretations in 8 discs, 7 of which had been judged by both observers to have indistinct boundaries of the disc or cup.
Biometry of the silicone oil-filled eye.
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Biometry of the fetal cisterna magna: estimates of the ability to detect trisomy 18.
Measurements of the fetal cisterna magna were obtained from a prospective sample of patients undergoing diagnostic obstetric ultrasound examinations. These normal measurements were then compared to a retrospective sample of ultrasound scans from fetuses with the diagnosis of trisomy 18 by amniocentesis. The fetal cisterna magna increases in size throughout pregnancy. The sample from fetuses with trisomy 18 was different and had a higher rate of small and large cisterna magnas. After the two samples were mixed, it was determined that a cut-off of 2.5 standard deviations for the fetal cisterna magna would give a sensitivity of 26.3%, specificity of 99.1%, positive predictive value of 50.0% and negative predictive value of 97.6% for trisomy 18. The probability that a fetal cisterna magna of abnormal size will predict trisomy 18 in an early second-trimester ultrasound examination with the 2.5 standard deviation cut-off was estimated at 0.019. A fetal cisterna magna that is of abnormal size appears to be of diagnostic value in identifying the fetus with trisomy 18, but its sensitivity is low.
Reference values for fetal limb biometry at 10-14 weeks of gestation.
OBJECTIVES: To calculate reference ranges for fetal limb measurements obtained by transabdominal ultrasound at 10-14 weeks of gestation. METHODS: Six hundred and six normal fetuses were examined transabdominally in a cross-sectional study by a single observer. The crown-rump length of the fetuses ranged from 31 to 78 mm. Measurement of the length of the humerus, ulna, femur, tibia and foot was attempted from the longest section of each structure. To assess intraobserver repeatability, three sets of repeated measurements were obtained in 26 fetuses. RESULTS: An appropriate ultrasound measurement was obtained in a percentage of cases ranging from 93.2% to 97.9%. A significant correlation was found between crown-rump length measurements and humerus length (r = 0.74, P < 0.001), ulna length (r = 0.70, P < 0.001), femur length (r = 0.77, P < 0.001), tibia length (r = 0.69, P < 0.001) and foot length (r = 0.58, P < 0.001). Crown-rump length-specific reference ranges for each measurement were calculated with the method of scaled absolute residuals. The study of intraobserver variability showed coefficients of variation ranging from 7.9 to 10.0% and intraclass correlation coefficients ranging from 0.89 to 0.94. CONCLUSIONS: Fetal limb size is strongly correlated with crown-rump length. Despite a significant biological variability of the measurements, the availability of reference ranges could be of help in the early diagnosis of fetal skeletal dysplasias.
[Medical biometry: statistics or black magic?].
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Impact of prenatal tobacco smoke exposure, as measured by midgestation serum cotinine levels, on fetal biometry and umbilical flow velocity waveforms.
The aim of this prospective cohort study was to evaluate the impact of tobacco smoke exposure, measured by maternal serum concentration of cotinine, on fetal midgestation biometric parameters and umbilical artery (UA) qualitative blood flow indices. The study population consisted of 114 healthy women in 20 to 24 weeks gestation who were recruited from the patients of two antenatal care units in Lodz, Poland. Significant negative correlation was found between fetal biparietal diameter (BPD) and serum cotinine concentration. Serum cotinine positively correlated with all blood flow indices under study (systolic/diastolic index [S/D], resistance index, and pulsatility index) after controlling for gestational age, gender, and femur length. The midgestation UA S/D ratio > 3 was found to be a significant risk factor for decreased birthweight. Tobacco smoke exposure is a significant factor inducing increased resistance of umbilical blood flow as measured in 20 to 24 weeks gestation. This could be one of the main mechanisms leading to decreased birthweight observed among infants with prenatal exposure to tobacco smoke.
[Ultrasound biometry in childhood].
Within the last 18 months the authors have measured, in cases of juvenile cataract seen by them, the axial length of the eye and other parameters. As a control group, children from the authors' squint clinic, with various refractive errors, were examined. With the data thus gathered, correlation and regression analyses were performed, postoperative refraction values were calculated, and eye growth in phakic eyes was compared with that in aphakic eyes. Regression formulas were established which enabled the authors to calculate eye length at a given age, to determine the postoperative refraction of their juvenile cataract patients with great accuracy, and, so far, to prove that there is no significant difference between phakic and aphakic eyes as regards growth.
[Biometry of the lens with respect to age and cataract morphology. Evaluation of Scheimpflug photos of the anterior segment].
Thickness of the lens, cortex and nucleus or nucleus with supranuclear layer, respectively, were determined for 58 controls aged 11-69 years (115 lenses), and for 175 patients aged 30-86 years with different types of cataract (247 lenses). Measurements of the densitograms of Scheimpflug photos (taken along the optical axis, magnified 10-fold) were performed, accurate to 0.5 mm (corresponding to 0.05 mm original size). The cataractous lenses were grouped in 5 morphological classes and 3 degrees of opacification (density according to the Scheimpflug photos). As regards normal lenses, the present authors' findings correspond to earlier findings of Niesel et al. (1976). Deviations from the normal pattern are found in typical cortical cataract (water-cleft and spokes cataract, wedge-shaped cataract) where nucleus and nucleus with supranuclear layer are thinner than the normal lenses, while with nuclear cataracts and mixed types the opposite is the case. In eyes with posterior cortical opacities no increase in the thickness of the anterior cortex is found with aging. With the true nuclear cataracts the increase in the thickness of the anterior cortex is negligible. The degree of opacification is closely related to an increase in the thickness of the nucleus and supranuclear layer, which implies a decrease in the thickness of the anterior cortex. Water-clefts and spokes of larger size cause the anterior cortex to become thinner. In eyes with wedge-shaped cataracts the different degrees of opacification did not affect the parameters measured.
[New technique of ultrasonic biometry (author's transl)].
A new measuring system for echo return times is described, which renders it possible to measure simultaneously the three axial lengths of the living eye (length of cornea plus anterior chamber, length of the lens and of the vitreous) with ultrasound in real time and to process the data numerically. The repetition rate for the measurements is optimized up to the limit: each transmitted wave is registered. The computer either generates a measuring protocol with statistical data (mean value, standard deviation) or the variation of the three echo return times is displayed graphically. In clinical practice the unit is used routinely for rapid determination of optimal implant lenses, etc.
Anterior chamber angle biometry: quadrant variation, age change and sex difference.
PURPOSE: To estimate the anterior change angle width (ACAW) in healthy volunteers quantitatively using an anterior eye segment analysis system and to clarify the involvement of aging and sex in ACAW. METHODS: The ACAW of the upper, lower, medial, and lateral quadrants of 42 eyes from 42 healthy volunteers was measured by the NIDEK EAS-1000 anterior eye segment analysis system, a non-invasive in vivo measuring method based on Scheimpflug image analysis. Data from all subjects were employed to investigate aging and quadrant differences; and age-matched male and female subjects were chosen from all subjects to study sex difference and aging. RESULTS: Young subjects showed no significant inter-quadrant differences of ACAW. However, ACAW showed a significant negative correlation with age in all quadrants, but the lateral quadrant showed much more narrowing than the others. The age-matched study revealed that ACAW narrowing was much greater in females than in males, and a polynomial regression analysis showed that this sex difference appeared in subjects older than middle age. CONCLUSIONS: The anterior eye segment analysis system revealed that ACAW decreased with age, especially in the lateral quadrant. The significantly more marked narrowness of ACAW in females older than middle age may be related to the high incidence of angle closure glaucoma in elderly females.
Fetal biometry: size and configuration of the third ventricle.
PURPOSE: To evaluate the normal configuration and size of the third ventricle in second and third trimester fetuses in a normal population, and to compare our values with those of previously published studies. MATERIAL AND METHODS: Evaluation of fetal third ventricular width and configuration was obtained by antenatal ultrasonography in 474 fetuses with gestational age between 12 weeks and term (mean 28 weeks). Percentiles for third ventricle width were estimated by combining separate fractional polynominal regression models fitted to the mean and standard deviation, assuming that the measurements had a normal distribution at each gestational age. Appearance of the third ventricle was correlated with each gestational age. RESULTS: The third ventricle could be visualized in 471 (99%) of 474 fetuses. The 97th percentile of the third ventricle in preterm fetuses was measured as 3.6 mm in size. The third ventricle was seen as a single echogenic line in 153 (32.4%) of 474 fetuses. Two-hundred-and-ninety-nine (61.5%) of all fetuses had parallel echogenic lines outlining a fluid-filled lumen. V-shaped third ventricular configuration was seen in only 28 (5.9%) of the fetuses. From 24 weeks to term, parallel echogenic lines were the most commonly (83.7% to 79.6%) encountered configuration for the third ventricle. CONCLUSION: The 97th percentile of the third ventricle in preterm fetuses was measured as 3.6 mm in size. In the early second trimester, 77% of the fetuses had a single echogenic line appearance on ultrasonography. As the brain and ventricular structures mature, a parallel echogenic line becomes the prominent ultrasonography appearance (>80% of fetuses) in third trimester healthy fetuses.
P.C. Mahalanobis' contributions to biometry: a note written on the occasion of his birth centenary.
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Chaos in biometry.
Although the study of chaotic and periodic phenomena began as recently as the 1960s, its subsequent development during the past few years has been extremely rapid in terms of both theory and practical application. The purpose of this paper is therefore to present an overview which will enable researchers with little prior knowledge to assess the relevance and potential application of nonlinear systems to problems in medicine and biology. Deterministic dynamic behaviour is examined through discrete logistic-type equations; stochastic behaviour is studied by superimposing an appropriate birth-death structure. Analysis of a variety of insect data sets shows that periodic and chaotic structures do indeed feature in natural populations; the classic Nicholson's blowfly data are viewed from both stochastic limit-cycle and deterministic chaos standpoints. Determination of the attractor dimension can be an invaluable aid to the understanding of biological and medical phenomena, and convincing examples include phase-space comparisons between healthy and sick humans for both EEG and ECG records.
Microcomputer software applied to corneal stromal biometry.
Here we report a new method for image analysis of the corneal stroma. To obtain the biometric characteristics of a given area, we perform three different treatments of the same image. These automated predictions closely match each parameter (length, surface area, etc.), as measured manually by a "blind investigator." Furthermore, to obtain quantifiable, average values, we have increased the number of successive image measurements, which has led to the development of a series of programs designed to optimize automated data handling. Finally, the acquired, calculated parameters are summarized in the form of intermediate tables for each series of images, and as a final summary table incorporating t-test values and permitting comparison between two stromas (e.g., normal and pathological). Multivariate analysis and an ascending hierarchical classification demonstrate the main trends in differences of pathological vs. normal stroma.
Ophthalmic biometry using ultrasound.
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