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At least 577 records · Page 32Linked to original sources

PubMed2003

Clinical assessment of the Zeiss IOLMaster.

PURPOSE: To compare axial lengths and intraocular lens (IOL) power calculations obtained with the Zeiss IOLMaster by 2 observers with different training grades and to assess the agreement between optical and acoustic biometry. SETTING: Department of Ophthalmology, Pembury Hospital, The Laser Eye Clinic, Kent, United Kingdom. METHODS: In this prospective study, optical biometry was performed twice in 79 patients: first by a qualified ophthalmic nurse and second by 1 of several health care assistants without formal nursing training. In the same group of patients, the qualified nurse also obtained ultrasonic measurements to compare the 2 clinical methods. RESULTS: There was a high correlation coefficient for axial length and IOL power measurements (0.99 each) between the experienced examiner and the inexperienced examiners. The coefficient of repeatability (2 SD) was 0.58 diopter (D) for IOL power (mean 0.04 D) and 0.07 mm for the axial length (mean 0.00 mm). The correlation coefficient of IOLMaster measurements with A-scan measurements done by the same experienced ophthalmic nurse was 0.97 for IOL power and 0.98 for axial length. The limits of agreement (mean +/- 2 SD) were between +0.50 and -2.40 D for IOL power calculations and between +0.7 mm and -0.2 mm for axial length measurements. CONCLUSIONS: Optical biometry showed excellent repeatability using different examiners regardless of their medical training. The agreement with ultrasonic measurements and the precision of the method need further evaluation.

Biometry↗

PubMed1990

Comparison of A-scan device accuracy.

A-scan biometry is recognized as a useful aid in predicting intraocular lens power. Measurements are reported to be accurate to better than +/- 0.1 mm. Three biometry devices were compared in examinations of 159 persons, each examination being repeated several times. Axial length averaged 23.77 mm when measured by the immersion technique; applanation and modified applanation techniques yielded 0.1 mm and 0.3 mm shorter distances, respectively. Measured values of axial lengths did not have the same probability of being measured, even if they were close together. Results were not distributed in smooth Gaussian curves; on the contrary, clusters of values, on the pattern of our choice of ultrasound wavelength, were seen even when biometry was performed with electronic gates in the devices. Retest reliability decreased when short distances in the anterior segment of the eye were measured. Measurements of lens thickness were less readily reproducible in cataractous lenses than in healthy young eyes; anterior chamber depth, on the other hand, was measured more reliably in cataract patients. This last finding may have resulted in part from uncertainties about ultrasound velocity in the cataractous lens and in part from accommodation. In cataract patients, axial length was measured most reproducibly by the immersion technique; it was measured less accurately in young healthy eyes with a modified applanation device.

Adolescent↗

PubMed1999

Per-operative retinoscopy as a predictor of final post-operative refraction.

PURPOSE: To assess the accuracy of streak retinoscopy performed at the end of cataract surgery as a predictor of final post-operative error. METHOD: Retinoscopy was performed on 68 patients as they lay on the operating table after routine cataract extraction and intraocular lens implantation. In each case the predicted post-operative refraction by biometry and the retinoscopy at the end of the operation were compared with the 6 week post-operative subjective refraction. RESULTS: The retinoscopy had a mean difference of 0.6 D (standard deviation of 0.5 D). The post-operative refraction predicted by biometric measurements had a mean difference of 1.6 D (standard deviation 0.6 D). When corrected for systematic error, 8% of patients were found to have an error of greater than 2 D as predicted by pre-operative biometry. Prediction by retinoscopy made no error greater than 2 D. The accuracy in the retinoscopic prediction of post-operative refraction was significantly better than the biometry using the F-test (p = 0.001). CONCLUSION: Retinoscopy at the end of cataract surgery may be a valuable tool to alert the surgeon to an unexpected refractive error. This would enable immediate intraocular lens exchange, if required.

Biometry↗

PubMed2001

Ratio of nuchal thickness to humerus length for Down syndrome detection.

OBJECTIVE: Ultrasonographic biometry markers are now being used clinically to adjust Down syndrome risk. The limitations are that the definitions of "abnormal" measurements used are arbitrary, thus reducing screening performance, and also that patient-specific Down syndrome risks cannot be calculated. We report a new ultrasonographic algorithm that is sensitive for Down syndrome detection and that estimates individual risk. STUDY DESIGN: Overall in fetal populations with Down syndrome the humerus length is decreased, whereas the nuchal thickness is increased relative to that of a normal population. The nuchal thickness/humerus length ratio therefore shows an even greater increase and magnifies the separation between Down syndrome and healthy groups. Prospective data were collected in midtrimester amniocentesis cases. A regression equation for the median nuchal thickness/humerus length ratio based on biparietal partial diameter was generated. The Down syndrome likelihood ratio, or the odds on the basis of the nuchal thickness/humerus length ratio (multiples of the median), was multiplied by the age-related risk to give the posterior Down syndrome risk. Charts for rapid estimation of individual Down syndrome risk on the basis of maternal age and the nuchal thickness/humerus length ratio were constructed. RESULTS: There were 94 cases of Down syndrome and 4700 cases in which the karyotype was normal. The mean (+/-SD) gestational age of the study population was 16.1 +/- 1.6 weeks. Thirty-three fetuses with Down syndrome and 68 karyotypically normal fetuses had gross anomalies. The equation for the expected median nuchal thickness/humerus length ratio was as follows: 10e(1.7163 - 0.0292) x BPD + 0.0003 x BPD2, where BPD is the biparietal diameter. In the overall study population the nuchal thickness/humerus length ratio and maternal age had a 79.8% detection rate at a 22.1% false-positive rate, compared with maternal age plus humerus length (sensitivity, 55.1%) or maternal age plus nuchal thickness (sensitivity, 66.7%) at the same false-positive rate. For women > or =35 years old the values were 80% and 22.0%, respectively. CONCLUSIONS: We report an ultrasonographic biometry algorithm that, in combination with maternal age, detects 79.6% of Down syndrome cases in a high-risk group. Individual Down syndrome risk can be quickly calculated at the bedside and made available to women who desire this information before making a decision on amniocentesis. On the basis of published standards, ultrasonographic biometry as described would be a cost-effective alternative to amniocentesis in this high-risk group.

Algorithms↗

PubMed2006

Fetal sheep development on ultrasound and magnetic resonance imaging: a standard for the in utero assessment of models of congenital abnormalities.

OBJECTIVE: To establish normative data for the size, conspicuity, and imaging characteristics of normal developing fetal sheep organs on ultrasound (US) and magnetic resonance (MR) imaging. METHODS: US and MR images of ten normal pregnant sheep, at 40, 65, 90, 115, and 140 gestational days (term = 145 days), were scored for organ conspicuity and imaging characteristics. Imaging biometry was correlated with specimens. Gestational age-based growth parameters were modeled using regression. RESULTS: Imaging biometry showed excellent correlation with specimens. Kidney, bladder, stomach, lung, liver, and spine were seen well from 65 days to term by US. More organs were consistently visible from 90 days to term by MR than by US. Most organ imaging characteristics tended not to change throughout gestation. CONCLUSION: Normal fetal sheep biometry, organ conspicuity, and imaging characteristics are established for US and MR and have potential use for the in utero assessment of sheep models of congenital abnormalities.

Animals↗

PubMed1985

Intraocular lens power calculations: the optimal approach.

The differences were studied between retrospectively calculated emmetropizing intraocular lenses and lenses estimated from different methods and formulas, either with or without the use of ultrasonic biometry. A number of 201 eyes was involved. The results show that ultrasonic biometry is an indispensable tool for the prediction of the power of intraocular lenses, which would produce emmetropia. The best results were obtained when using biometry and the simple empirical SRK formula.

Biometry↗

PubMed2006

Comparison of partial coherence interferometers: Acmaster versus laboratory prototype.

PURPOSE: To evaluate anterior segment biometry using the ACMaster (Carl Zeiss Meditec AG, Jena, Germany) in regard to precision of measurement and clinical performance compared to the original laboratory prototype of the partial coherence interferometry technique. METHODS: Ten phakic (20 eyes) and 27 pseudophakic (44 eyes) patients were included in this study. Anterior segment biometry of phakic and pseudophakic study eyes was performed using the ACMaster and the laboratory prototype of the partial coherence interferometry technique. The ACMaster is a commercially available device based on the partial coherence interferometry technique, which provides high precision anterior segment measurements in a quick and user-friendly fashion. Examination included measurement of central corneal thickness, anterior chamber depth, and lens thickness, the latter only in the phakic eyes. RESULTS: The consistency of anterior segment measurements performed with both units was excellent in phakic as well as in pseudophakic eyes. In pseudophakic eyes, the measurement of anterior chamber thickness and lens thickness with the ACMaster produced several (typical) measurement artifacts in some cases, which partially aggravated the identification of the A-scan peak representing the anterior intraocular lens surface. CONCLUSIONS: The ACMaster is a user-friendly device that enables axial anterior segment biometry using the partial coherence interferometry technique with a reproducibility similar to that of the original laboratory prototype.

Anterior Eye Segment↗

PubMed2003

Ultrasonographic measurement of optic nerve sheath diameter in normal dogs.

This study was carried out to assess the feasibility of ultrasonographic measurements of the optic nerve sheath diameter (ONSD) in normal dogs and evaluate the effect of breed, sex, body weight and age on biometry of ONSD. The ONSDs were evaluated in 15 dogs (10-50 months old) with normal eye (7 Yorkshire terrier and 8 Maltese). Ultrasonographic measurements of the ONSD were carried out at a constant position located 5 mm behind the optic disc. Eyes were collected immediately after euthanasia, and were used for saline immersion technique and direct measurement by calipers for biometry of ONSD. In this study, there was no significant difference of ONSD between the left and the right eyes, and was no significant difference among ONSD values obtained from ultrasonographical method, saline immersion technique and direct measurement (k=0.95). Also, there was no correlations between ONSD and sex, body weight and age, but was significant between the mean ONSD of Yorkshire terrier and Maltese (p<0.01). The mean ONSD of Yorkshire terrier was 2.10 +/- 0.22 mm and Maltese was 1.63 +/- 0.23 mm. This study suggests that ultrasonographic measurements is useful method for biometry of the ONSD in normal dogs and provides baseline information for the study of evaluating ONSD in various breeds and diagnosing several diseases with the change of the ONSD.

Age Factors↗

PubMed2005

Fetal growth in Peru: comparisons with international fetal size charts and implications for fetal growth assessment.

OBJECTIVES: To compare fetal biometry measurements obtained in a Peruvian population with reference fetal size charts obtained in Peruvian and non-Peruvian populations. METHODS: Fetal biometry measurements collected prospectively in 195 uncomplicated pregnancies were included in the presented analysis. At 20, 24, 28, 32, 36 and 38 weeks' gestation, fetal head circumference, abdominal circumference and femur diaphysis length were measured. Fetal biometry measurements were compared with fetal size charts obtained from another Peruvian and two non-Peruvian populations from North America and Europe. RESULTS: When compared with ultrasound-based reference fetal size charts obtained from North American and European populations, fetuses from the studied population appeared to grow more slowly with advancing gestational age. This trend was not observed when a Peruvian population, similar to the one studied here, was used as a reference. CONCLUSIONS: The results suggest that fetal growth in this Peruvian population may not be adequately assessed by using reference charts obtained from other populations and have implications for the use of growth standards in antenatal management.

Abdomen↗

PubMed2005

Analysis of Z-score distribution for the quality control of fetal ultrasound measurements at 20-24 weeks.

OBJECTIVES: To develop and evaluate the feasibility of Z-score distribution-based quality assessment for fetal biometry at 20-24 gestational weeks. METHODS: Four sonographers measured fetal biparietal diameter, head circumference, abdominal circumference and femur length in unselected pregnancies undergoing routine sonography at 20-24 weeks in our center between June 2001 and January 2004. All measurements were transformed into Z-scores. Distributions of Z-scores were compared with the expected standard normal distribution based on mean, SD and the Kolmogorov-Smirnov test. Modelling was performed to assess the sensitivity, specificity and Youden's index (sensitivity + specificity - 1) of each sonographer, reflecting their ability to detect fetuses with abnormal biometry in our population. RESULTS: A total of 5241 ultrasound examinations were included. None of the Z-score distributions could be considered similar to the standard normal distribution: means of Z-scores ranged from -0.604 to 0.73 and the SD ranged from 0.726 to 0.896. Sensitivity and specificity ranged from 25.31% to 68.67% and 93.44% to 100%, respectively; Youden's index ranged from 0.25 to 0.69. CONCLUSION: Analysis of Z-score distribution can be used to assess the quality of fetal measurements. Several indices can be extracted from this analysis in order to improve quality assessment of fetal biometry measured by ultrasound.

Abdomen↗

PubMed1992

[What is the contribution of Doppler sonography of the umbilical artery in diagnosis of intrauterine growth retardation?].

Pulsed Dopplersonography of the umbilical artery was performed in 155 singleton high-risk pregnancies without malformations or chromosomal abnormalities. 59 foetuses were classified as foetuses with intrauterine growth retardation (IUGR). 46 of them had a birth weight below the tenth percentile. In 20 cases the pulsatility index (PI) was elevated (sensitivity: 44%). In all there were 50 neonates with a birth weight below the tenth percentile, 46 of whom were detected by biometry (sensitivity: 92%). 8 dystrophic neonates with a biometry that revealed IUGR were compromised by perinatal asphyxia. In six cases operative delivery was necessary and two cases with reversed diastolic flow ended in intrauterine foetal death. 7 of those foetuses had an elevated PI. The sensitivity of Dopplersonography in this group was 88%, the negative predictive value 97%. The positive predictive value with regard to a dystrophic neonate can be improved from 78% to 91%, if compared with biometry alone. Summing up, Dopplersonography of the umbilical artery can distinguish very well between IUGR foetuses at risk of perinatal morbidity or mortality and those IUGR foetuses with sufficient placental circulation who are, therefore, not at risk.

Asphyxia Neonatorum↗

PubMedDate not supplied

Maternal psychological distress, prenatal cortisol, and fetal weight.

OBJECTIVE: The objective of this study was to examine the effects of maternal psychological distress on estimated fetal weight during midgestation and explore the maternal hypothalamic-pituitary axis and sympathoadrenal dysregulation as potential risk factors for these effects. METHODS: Fetal ultrasound biometry measurements and maternal sociodemographic characteristics, emotional distress symptoms, and first morning urine samples were collected during a clinical ultrasound examination for a cross-sectional sample of 98 women who were between 16 and 29 weeks pregnant. Fetal weight was estimated from ultrasound biometry measurements; maternal emotional distress was assessed using the daily hassles (stress), Center for Epidemiologic Studies-Depression (depression), and State-Trait Anxiety Inventory (anxiety) scales; and urine samples were assayed for cortisol and norepinephrine levels. RESULTS: Correlation analyses revealed that both maternal psychological (daily hassles, depression, and anxiety) and biochemical (cortisol and norepinephrine) variables were negatively related to fetal biometry measurements and estimated fetal weight. A structural equation model further revealed that when the independent variance of maternal sociodemographic, psychological distress, and biochemistry measures were accounted for, prenatal cortisol was the only significant predictor of fetal weight. CONCLUSIONS: Women exhibiting psychological distress during pregnancy exhibit elevated cortisol levels during midgestation that are in turn related to lower fetal weight.

Adult↗

PubMedDate not supplied

Pupillary dilation and axial length measurement for preoperative assessment of intraocular lens power.

Cataract extraction is now routinely followed by insertion of an intraocular lens (IOL) which requires preoperative biometry to determine the most accurate implant power required. Biometry is generally performed just prior to surgery and may even require the patient to make a special hospital visit when day case surgery is contemplated. A prospective study was undertaken to determine the accuracy of axial length (AL) measurement through a dilated pupil. The AL of one eye of 64 patients admitted for cataract surgery was measured before and after dilation with a drop of tropicamide 1%. Our results show that there was no significant difference in the ALs before and after dilation (p = 0.10), and neither was there a difference in the average range of measurements (p = 0.70), with 78% of eyes having a difference of < +/- 0.3 mm between pre and post dilation ALs. We conclude that AL measurement performed on a dilated pupil can give an accurate result, and suggest that performing biometry on a dilated pupil following ocular assessment may be an efficient and time saving exercise.

Aged↗

PubMed1999

Knapp's law and unilateral axial high myopia. 1970.

BACKGROUND AND PURPOSE: (Hermann) Knapp's Law states, in essence, that in axial ametropia, if the correcting lens is placed so that its second equivalent point coincides with the anterior focus of the eye (ca 15 mm in front of the eye), the size of the retinal image is not different from that in the normal eye. The advent of ocular ultrasonic echography and axial biometry permits us to now test this Law. METHODS AND SUBJECTS: A "Direct Comparison" Eikonometer was devised using the Aulhorn Phase- Difference Haploscope, projectors, and half circle targets with equalized luminance. Five patients with anisomyopia were tested for aniseikonia after complete ophthalmologic examination including also A-Scan ultrasonic echography axial biometry. RESULTS: Significant aniseikonia was found in all five subjects ranging from 10% to 60% angular minification in the myopic eye. Ultrasonic axial biometry showed axial length differences from 2 to 5 1/2 mm with reasonable correlations between axial length differences and both clinical ametropia (anisomyopia) and the amount of aniseikonia found. CONCLUSIONS: Knapp's Law may be optically right but clinically wrong. That is, its clinical application, which predicts the absence of aniseikonia in axial aniosometropias is not fulfilled. Retinal stretching due to myopia and resultant retinal micropsia is hypothesized to be the cause of this optically unexpected aniseikonia. The retinal images may be isometric but the patient will still have significant cortically perceived or perceptual aniseikonia due to retinal microspia. Such patients may benefit from contact lenses or other aniseikonic corrections.

Aniseikonia↗

PubMed1986

Factors affecting intraocular lens power calculation.

Intraocular lens power calculation is increasing in use in the United Kingdom. Primarily to avoid anisometropia, intraocular lens power calculation may also be used to provide the patient with three rather than two working distances, but to achieve this greater accuracy of IOL power calculation is required. Using the SRK regression formula, three groups of patients have been studied. The effect of inaccurate use of the formula of choice is shown and the need to modify the 'A' constant to account for variation both in technique and biometry equipment emphasised. The variation in results due to inaccurate biometry are statistically assessed. Accuracy of IOL power calculation requires consistency but not absolute accuracy in biometry. No ocular factors were found to affect the accuracy of IOL power calculation.

Anthropometry↗

PubMedDate not supplied

First and second trimester sonography: an American perspective.

In the United States, first-and second-trimester ultrasonography is most commonly used for gestational dating, detection of fetal aneuploidy, identification of early fetal intrauterine growth restriction (IUGR), and assessment for cervical incompetence. Crown-rump length (CRL) between 7 and 12 weeks is the most accurate parameter for first-trimester dating. In the second trimester, the biparietal diameter, head circumference, transverse cerebellar diameter (TCD), abdominal circumference, femur length, and other long bones, such as tibia and humerus, are useful. The TCD appears to be particularly useful because of its relative sparing in IUGR. Ultrasound can aid in the detection of fetal aneuploidy by identifying structural anomalies or abnormal fetal biometry in the first and second trimester. Numerous structural abnormalities are suggestive of aneuploidy. Cystic hygroma and nuchal translucency appear to be most significant first-trimester markers for fetal aneuploidy. Second-trimester estimated fetal weight (FFW) curves have been developed and are useful in the early detection of IUGR. Second-trimester FFW curves are useful for the detection of trisomy 18 (sensitivity 60%) but not for trisomy 21 (sensitivity 8-12%). Fetal biometry of long bones is also useful in identifying fetuses at risk for aneuploidy. Identification of a second-trimester fetus with either humerus or femur shorter than expected places the fetus at risk for aneuploidy. The sensitivity of short long bone in detection of fetal aneuploidy is approximately 30%, with false positive rates < 5%. Nuchal fold thickness > 6 mm in the second trimester is also used for identifying aneuploid fetuses. The overall sensitivity for the detection of Down's syndrome in fetuses with increased nuchal fold thickness is approximately 34% and the false positive rate is 1.5%. We have developed a model by using an ultrasound examination to adjust the mid-trimester risk for trisomy 21 by combining maternal age or triple screen risk assessment (unconjugated estriol, alpha fetoprotein, and human chorionic gonadotropin) and ultrasound. Using this model, the risk for Down's syndrome is found to be increased with identification of abnormal biometry or anomalies, or decreased with a normal genetic ultrasound examination. Another important application is the use of abdominal and transvaginal ultrasound in the second trimester in pregnancies at risk for premature cervical dilatation, premature delivery, and cervical incompetence. We have found transfundal pressure to be useful in the diagnosis of otherwise clinically inapparent premature cervical dilatation and cervical incompetence.

Aneuploidy↗

PubMed2003

Ultrasonographic biomicroscopy, Scheimpflug photography, and novel provocative tests in contralateral eyes of Chinese patients initially seen with acute angle closure.

OBJECTIVES: To compare ocular biometry of the contralateral eyes of individuals seen with acute angle closure (AAC) with eyes of population-based control subjects, and to assess novel provocative tests to study the mechanism of AAC. DESIGN: Prospective case-control study. PARTICIPANTS: Chinese persons seen as incident cases of AAC and Chinese population-based controls. METHODS: Slitlamp assessment, ultrasonographic biomicroscopy, Scheimpflug photography, and provocative testing were performed. MAIN OUTCOME MEASURES: Ocular biometric parameters including anterior chamber depth, limbal anterior chamber depth, axial length, lens thickness, and radius of corneal curvature were obtained. Ultrasonographic biomicroscopy parameters that include the angle-opening distance at 500 micro m and the angle-recess area were noted. Scheimpflug photography produced a single measure of angle width. RESULTS: Contralateral eyes of cases of AAC had shorter axial lengths, shallower anterior chamber depths, thicker lenses, and steeper radii of corneal curvature (P<.01). After adjusting for age and sex, cases had a mean adjusted axial length that was 1.2 mm shorter, an optical anterior chamber depth that was 0.63 mm shallower (24% shallower than controls), and lenses that were, on average, 0.35 mm thicker (P<.01). Furthermore, using multiple logistic regression to adjust for age and sex, patients with primary angle-closure glaucoma were 19 times as likely to have a shallower limbal anterior chamber depth (25%; 95% confidence interval, 8.3-45.2). Adjusting for age and sex, the mean angle-opening distance at 500 microm was 0.14 U less for cases, with a mean of 0.26 U in controls, making the angle-opening distance at 500 microm, on average, 54% less among cases. Scheimpflug photographs revealed an adjusted angle width of 21.6 degrees for controls and 15.1 degrees for cases (P<.05). Dynamic testing showed that the angle of control eyes tended to shallow less when going from light to dark and tended to open more when given 1 drop of pilocarpine hydrochloride. CONCLUSIONS: Contralateral eyes of individuals having an AAC attack tend to be shorter and have more crowded anterior segments than those of healthy controls. These static measures of ocular biometry indicate why some individuals are predisposed to AAC. Dynamic measures of the response to luminance changes and pilocarpine therapy indicate that differential reactions to these stimuli are also associated with an AAC attack.

Acute Disease↗

PubMed2006

Fetal echocardiography during routine first-trimester screening: a feasibility study in an unselected population.

OBJECTIVE: To evaluate the feasibility of obtaining standard echocardiographic views of the fetal heart during routine first-trimester screening and construct reference ranges for cardiac biometry at 11 + 0 to 13 + 6 weeks of gestation. METHODS: A cross-sectional study of 584 fetuses in an unselected population. Viable pregnancies with a crown-rump length (CRL) of 41-78 mm were included. Echocardiography was performed by a single obstetrician using a 5 to 7.5 MHz vaginal transducer. The course and outcome of pregnancies were recorded and information on the babies was obtained in all cases. RESULTS: A completely satisfactory visualization of the fetal heart structures was possible in 58% (43%, 56% and 62% at 11, 12 and 13 weeks, respectively). Reference ranges were constructed from the measurements of cardiac ventricles, their outflow tracts, and cardiothoracic circumference ratio in relation to CRL. CONCLUSION: Standard echocardiograhic views of the fetal heart can be obtained at 11 + 0 to 13 + 6 weeks of gestation using the transvaginal approach. New reference ranges were established for fetal cardiac biometry at 11 + 0 to 13 + 6 weeks of gestation.

Adolescent↗