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At least 91 records · Page 5Linked to original sources
PubMed1998

High precision biometry of pseudophakic eyes using partial coherence interferometry.

PURPOSE: To investigate the applicability of the scanning version of dual-beam partial coherence interferometry (PCI) for measuring the anterior segment and axial length of pseudophakic eyes in a clinical setting and to determine the achievable precision with this biometry technique. SETTING: Department of Ophthalmology, Vienna General Hospital, and Institute of Medical Physics, University of Vienna, Austria. METHODS: Partial coherence interferometry was performed in 39 pseudophakic eyes of 39 patients after implantation of a foldable acrylic intraocular lens (IOL). RESULTS: Effective lens position (ELP), IOL thickness and lens-capsule distance (LCD) were determined with a precision of 2 to 3 microns; corneal thickness and axial eye length, with a precision of 0.8 and 5.0 microns, respectively. The mean ELP of the IOL was 4.093 mm +/- 0.290 (SD). In 7 eyes (18%), a positive LCD of 68 +/- 40 microns was detected with PCI. Mean corneal thickness was 526.4 +/- 31.5 microns; mean IOL thickness, 791.5 +/- 40.2 microns; and mean axial length, 23.388 +/- 0.824 mm. CONCLUSION: The scanning version of PCI enables high precision (< or = 5 microns) and high resolution (approximately 12 microns) biometry of pseudophakic eyes that is better than conventional ultrasound by a factor of more than 20. For the first time, positive LCD, a possible risk factor for posterior capsule opacification, could be detected and quantified. Furthermore, this technique offers a high degree of comfort for the patient since it is a noncontact method with no need for local anesthesia or pupil dilation and has a reduced risk of corneal infection.

Acrylates↗
PubMed2003

Comparison of the Zeiss IOLMaster and applanation A-scan ultrasound: biometry for intraocular lens calculation.

PURPOSE: A comparison of axial length estimates using applanation A-scan ultrasound and the Zeiss IOLMaster was conducted. The accuracy in predicting postoperative refraction determined by each method was also compared. METHODS: A cross-sectional study was performed on 51 eyes in 46 patients presenting to clinical practice for cataract surgery assessment. Preoperative measurement of axial length was performed with applanation ultrasound and the IOLMaster. The IOLMaster measurements were used to determine the intraocular lens power based on the SRK/T formula. Postoperative refractive outcomes were obtained and spherical equivalent calculated and compared to the predicted refractive error with each biometric method. RESULTS: On average the axial lengths measured by the IOLMaster were longer by 0.15 mm compared to ultrasound biometry (P < 0.01). Using the IOLMaster over applanation ultrasound biometry significantly improved the postoperative refractive outcome from 0.65 D to 0.42 D (P = 0.011). CONCLUSIONS: The IOLMaster provides an accurate axial length measurement and results in accurate intraocular lens power calculation based on the SRK/T formula. It is quick and easy to use and provides a non-contact technique with no risk of infection or corneal abrasion.

Adult↗
PubMed2000

Combined ultrasound biometry, serum markers and age for Down syndrome risk estimation.

OBJECTIVE: To compare Down syndrome screening efficiency of the standard serum triple analyte screen to that of a four-component screen consisting of ultrasound biometry and serum markers in the second trimester. METHODS: The Down syndrome screening efficiency of the triple screen, i.e. alpha-fetoprotein (AFP), unconjugated estriol (E3), hCG and maternal age, was compared with the four-marker algorithm, i.e. humerus length, nuchal thickness, AFP and hCG plus maternal age. A quadrivariate Gaussian algorithm was used to calculate individual Down syndrome odds. Receiver operating characteristic (ROC) curves plotting sensitivity against false-positive rate were constructed for each algorithm and the areas under the curves were compared to determine which was superior. Sensitivity and false-positive rates at different Down syndrome risk thresholds were also compared. RESULTS: There were 46 cases of Down syndrome (1.9%) with 2391 normal singleton pregnancies in a referral population in which triple screen, fetal biometry and karyotype had been done. The gestational age range for the study was 14-24 completed weeks. The median maternal age for the study group was 35.0 years (14.0-46.0 years). The areas (SE) under the ROC curves were 0.75(0.04) and 0.93(0.02) for the standard triple and the four-marker screen, respectively (P < 0.001). At a 10% false-positive rate, detection was 45.7% for the triple and 80.4% for the four-marker screen. CONCLUSIONS: A new algorithm combining humerus length and nuchal thickness measurement with serum AFP, hCG and maternal age substantially improved Down syndrome screening efficiency compared with the traditional triple screen. The model appears promising and should be evaluated in an independent data set.

Adolescent↗
PubMed1998

[Intraocular lens calculation and ultrasound biometry: immersion and contact procedures].

BACKGROUND: Ultrasound biometry for axial length measurement may be performed either by directly putting the probe on the cornea or by using a water immersion technique. Our goal was to examine whether there are unsystematic differences between both techniques present besides systematic differences that can be compensated by adjusting calculation formula constants. PATIENTS, MATERIALS AND METHODS: We examined 288 patients in a prospective, randomized trial. There was no ocular pathology present beside cataract. Axial lengths < 21 mm and > 27 mm were excluded. We calculated which IOL power would have given the desired refractive result by using the postoperative refraction and data of the lens implanted. RESULTS: A systematic difference between both techniques is present. With the contact technique, axial length is measured 0.15 mm shorter. This requires adjustment of formula constants. Furthermore, there is an unsystematic difference that leads to 18% greater calculation errors (difference between IOL calculated preoperatively and ideal IOL) with the contact technique. Mean absolute error was 0.43 +/- 0.38 dpt for the immersion group and 0.53 +/- 0.48 dpt for the contact group. CONCLUSIONS: To minimize postoperative refractive errors, ultrasound biometry using immersion technique should be preferred.

Aged↗
PubMed2005

Biometry and intraocular lens power calculation.

This article surveys the literature of 1 year, between July 2003 and August 2004, on the topic of biometry and intraocular lens power calculation for cataract surgery. There is an increasing demand for low postoperative refractive error with rising patient expectations, especially with patients who have already undergone refractive surgery, and with developing intraocular lens technologies such as multifocal, accommodating, or toric intraocular lenses. Optical biometry has become an invaluable tool for axial length measurement, especially for a setting with a less experienced biometrist. Introduction of ray tracing for power calculation and new methods of dealing with power calculation in eyes that have undergone previous refractive surgery seem promising. New intraocular lens designs that allow adjusting the axial optic position and therefore the effective refractive power of the intraocular lens have been evaluated in animal studies.

Anterior Chamber↗
PubMed2007

Gender variation in ocular biometry and ultrasound biomicroscopy of primary angle closure suspects and normal eyes.

PURPOSE: To compare A-scan biometry and ultrasound biomicroscopy of primary angle closure suspects (PACS) with age-matched normal Indian eyes. PATIENTS AND METHODS: Subjects with primary angle closure suspects (n=57 eyes) and normal eyes (n=57 eyes) underwent A-scan biometry and ultrasound biomicroscopy. Anterior chamber depth (ACD), anterior chamber angle (ACA), axial length (AXL), lens thickness, relative lens position (RLP), central corneal thickness (CCT), angle opening distance 500, trabecular-ciliary process distance (TCPD), iris-ciliary process distance, iris thickness, and scleral-ciliary process angle were measured. The subjects were divided into males, females, and combined groups for analysis. The parameters were compared using independent sample t test with Bonferroni correction for multiple comparisons. RESULTS: In the combined group, the PACS subjects presented a significantly low ACD, AXL, CCT, AOD500, TCPD, ACA (P<0.001), and RLP (P=0.04). In males, RLP was anterior (P=0.002) and in females, the lens thickness (P<0.001) was significantly thicker among the PACS group. CONCLUSIONS: ACD, AXL, CCT, TCPD, ACA, and angle opening distance 500 of the PACS group were significantly lower than in normals. In females, the lens in PACS was thicker than in normals. Lens in males was more anterior-placed in PACS group than in normals.

Anterior Eye Segment↗
PubMed1995

Video controlled M-mode biometry.

To increase the accuracy of intraocular lens power calculation, an interface between an ultrasonic A-scanning device and a personal computer was created, allowing for an on-line interpretation of the ultrasonogram in an M-mode fashion. On the same computer display, a video recording of the movements of the transducer probe relative to the eye was inserted to obtain simultaneous information on the external alignment of the transducer probe. The precision of the experimental set-up in the measurement of intraocular distances was compared with conventional A-scanning procedures run in automatic mode. The video controlled M-mode biometry was found easy to operate and to result in reproducible axial length determination: The median value of the standard deviation was found to be below 0.04 mm as compared to a value of about 0.10 mm with conventional equipment. We concluded that video controlled M-mode biometry has great potential in the endeavour to increase the accuracy of intraocular lens calculation.

Anterior Chamber↗
PubMed1983

Ultrasonographic biometry in congenital glaucoma.

Method 'A' ultrasonographic biometry was performed on 23 patients with congenital glaucoma. The axial lengths of these eyes were significantly greater as compared to the 7 fellow eyes with normal intraocular pressures of the same patients and 10 eyes of 5 patients with megalocornea of the same age. Some of the borderline cases showed an increase of axial length during follow-up not attributable to normal growth. After successful surgery an early decrease of the axial length up to 0.8 mm could be seen. The change occurred in post-equatorial measurements. It is concluded that ultrasonographic biometry is a very valuable additional technique for the diagnosis and postoperative follow-up of congenital glaucomas.

Biometry↗
PubMed1990

Biometry of the crystalline lens in early-onset diabetes.

Lenticular biometry on non-cataractous lenses has been studied by means of Scheimpflug photography and digital image analysis in 153 patients with early-onset insulin-dependent diabetes and 153 non-diabetic controls. Anteroposterior axial lens thickness, cortical thickness, nuclear thickness, anterior and posterior lenticular curvatures, and anterior chamber depth were assessed. Highly significant differences between the lenses of the diabetic subjects and non-diabetic controls were found. After the effect of age had been accounted for within the diabetic subgroup, diabetic duration was found to be a highly significant determinant of lens dimensions, such that age-related dimensional changes for various biometric parameters were accelerated by between 52% and 121% after the onset of diabetes. Because the diabetic duration of the early-onset diabetic subjects studied in this work was accurately known, this report is the first in which a precise assessment of the effect of 'true' diabetic duration on lens biometry has been possible.

Adolescent↗
PubMed2003

Ocular biometry in occludable angles and angle closure glaucoma: a population based survey.

AIM: To compare ocular biometric values in a population based sample of eyes with occludable angles, angle closure glaucoma, and normal subjects. METHOD: 2850 subjects from a population based glaucoma prevalence study underwent complete ocular examination including indentation gonioscopy. Ocular biometry was performed in all subjects classified to have occludable angles (n = 143); angle closure glaucoma (n = 22), and a random subgroup of 419 normal subjects. Ocular biometry readings between the groups were compared and statistically analysed using "t," "z," and Mann-Whitney U tests. RESULTS: The mean age among subjects with occludable angles (54.43 (SD 9.53) years) and angle closure glaucoma (57.45 (8.5) years) was significantly higher (p<0.001) than normal subjects (49.95 (9.95) years). Axial length was shorter (p<0.001) in the occludable angle group (22.07 (0.69) mm) compared to the normal group (22.76 (0.78) mm). Anterior chamber depth (ACD) was shallower (p<0.001) among subjects with occludable angles (2.53 (0.26) mm) than normal subjects (3.00 (0.30) mm). Lens thickness (LT) was greater (p<0.001) in people with occludable angles (4.40 (0.53) mm) compared to normal subjects (4.31 (0.31) mm). No significant difference was noted in axial length, ACD (p = 0.451), and LT (p = 0.302) between angle closure glaucoma and occludable eyes. CONCLUSION: South Indian eyes with angle closure glaucoma and occludable angles seem to have significantly shorter axial lengths, shallower anterior chambers and greater lens thickness compared to the normal group.

Adult↗
PubMed2003

Optical biometry before and after excimer laser epithelial keratomileusis (LASEK) for myopia.

PURPOSE: In order to select the correct intraocular lens (IOL) for implantation, it is important to measure the eye length (biometry). The IOL Master from Zeiss-Humphry is frequently used for such measurements. Because this instrument employs an optical method, any irregularities on the corneal surface or any disturbances in corneal transparency could lead to mistakes in the measurements. The aim of this study was to determine whether eye length measurements obtained at the University Eye Clinic Regensburg, Germany with the IOL Master before and after excimer laser epithelial keratomileusis (LASEK) show any changes. METHODS: Axial length was measured on 20 myopic eyes (-2.75 to -8.00 diopters) before and one month after LASEK using the IOL Master. RESULTS: The mean pre-operative eye length was 25.46 mm (SD +/- 1.03) and the post-operative mean length was 25.38 mm (SD +/- 0.99). There was a strong correlation between the pre- and post-operative eye lengths (Pearson correlation coefficient 0.998). CONCLUSIONS: Although LASEK can lead to increased light scattering due to irregularities of the corneal surface and changes in corneal transparency, there is no difference in biometry pre- and post-operatively.

Adult↗
PubMedDate not supplied

Very high frequency ultrasound biometry of the anterior and posterior chamber diameter.

PURPOSE: To measure the largest diameter of the anterior chamber (AC) and posterior chamber (PC) dimension and its orientation and determine the relationship with the principal keratometric meridians. METHODS: Twenty-eight eyes of 14 subjects were scanned with high frequency (50 MHz) ultrasound in sequential meridional scan planes at 30 degrees increments. Observer identified angle and ciliary sulcus recess boundaries in each patient scan set were fit with an elliptical model to obtain the ellipse semi-major axis corresponding to the largest diameter and its meridional orientation. Anterior and posterior chamber diameters from raw data and model fit were compared using linear statistics. Circular statistics were used to compare the orientation of the largest diameter for raw ultrasound measurements, model estimations of largest diameter, and autorefractor determined keratometric axes. RESULTS: The mean model diameters were anterior chamber OD 12.07 mm (0.32 SD); anterior chamber OS 12.06 mm (0.36 SD); posterior chamber OD 12.35 mm (0.42 SD); posterior chamber OS 12.33 mm (0.43 SD). The general trend for orientation of the meridian of largest diameter was in the horizontal meridian. In over 35% of eyes the difference between AC or PC meridian and the flat keratometric axis was greater than 20 degrees. CONCLUSIONS: Accurate and reproducible anterior segment biometry depends on visualization of structures and minimization of eye and head movement error. The range and standard deviation of the diameter and orientation measures suggests anatomic variation is sufficient to require biometry for proper sizing and placement of intraocular devices that use angle or sulcus fixation.

Adult↗
PubMed2000

[Ultrasound foetal biometry in the town of Ouagadougou, Burkina Faso. Report of a cohort of 126 pregnant women].

PURPOSE: This inquiry on the ultrasound fetal biometry in the town of Ouagadougou aimed to study the fetal growth through the ultrasound biometry in order to compare it with other authors's works and to lay down a local chart. PATIENTS AND METHODS: This prospective study led from March 1997 to April 1998 The follow-up of 126 pregnant women allowed to lay down the graphs of following elements: biparietal diameter, cephalic circumference, transverse abdominal diameter, abdominal circumference and femur. RESULTS: The average age of the subjects was 26 years old+/-0.8 and 52.4% of them belonged to an average socio-economic level. All the studied parameters were closely connected with the age of pregnancy. The DAT and the abdominal circumference presented the greatest correlation (0.998). The comparison of our growth graphs with those of others authors led to notice significant differences as well as with African, European and American graphs. CONCLUSION: There is a need to lay down local charts in order to have a best estimation of the pregnancy age and the fetal growth.

Adolescent↗
PubMed2000

Charts of Thai fetal biometries: 1. Methodology.

A cross-sectional study was conducted in order to construct new reference charts for Thai fetal biometries that are commonly used in obstetric ultrasound practice. We discussed and illustrated a sound appropriate study design and statistical analysis which lead to more valid results. A total of 621 normal pregnant women between 12-41 weeks of gestation and their fetuses were recruited. Each fetus was measured once at a randomly assigned gestational age specifically for the purpose of this study only. Stepwise linear regression technique was used to model the mean and its standard deviation as functions of gestational age. Goodness of fit and normality of the data were checked before the final models were chosen. Reference centiles were derived, taking into account the increasing variation as pregnancy proceeds. We demonstrated the stated technique with humerus data from the same study. Reference charts for other fetal biometries have been derived and are presented in subsequent papers.

Anthropometry↗
PubMed2000

[Biometry 2000. Fetal growth charts by the French College of fetal ultrasonography and the Inserm U 155].

OBJECTIVE: The aim of Biometry 2000 was to establish reliable sonographic fetal auxology reference charts for biparietal diameter, head circumference, abdominal diameter, abdominal circumference and femur length. DESIGN: A prospective multicentric longitudinal and transversal study was carried out. SUBJECTS: The data of this study were obtained from 35,456 scans recorded in 10,043 women for a period of one year. METHODS: Sonographic measurements were performed using a single method for each parameter. Twins and unknown gestational ages were not included. No exclusions were made for small-for-age, congenital malformations or any event during pregnancy. Assuming measurements have a normal distribution, centiles were calculated after polynomial regression models from mean and standard deviation according to gestational age in exact weeks from last menstrual period. RESULTS: A total of 32,584 fetal biparietal diameters, 20,400 direct cephalic circumferences, 31,790 transverse abdominal diameters, 21,562 direct abdominal circumferences and 30,960 femur lengths were obtained. Fetal growth charts with means, standard deviations and centiles are presented. CONCLUSION: The multicentric study, Biometry 2000, has established sonographic fetal charts derived from a large sample of scans and unselected pregnant women assuming a normal distribution.

Abdomen↗
PubMed2001

Fetal biometry: a comparison of family physicians and radiologists.

BACKGROUND AND OBJECTIVES: While performance and reading of obstetric sonograms is a skill widely taught in family practice residency programs, no prior studies have compared ultrasound performance and interpretation in residency programs with that of hospital radiologists. This study compares results of fetal biometry for gestational age determination performed sequentially by faculty-supervised residents and radiologists. METHODS: This retrospective chart review selected cases from among all gravidas who had ultrasound performed in a family practice residency clinic between January 1992 and April 1999. Biometry was performed by residents under the supervision of faculty preceptors who had ultrasound training and experience. A patient was included if (1) results of both a family practice ultrasound and a radiologist-read hospital ultrasound were present in the chart, (2) both studies were done before 36 weeks gestation, and (3) the family practice examination preceded the hospital study. The difference in expected date of confinement between resident and radiologist ultrasound was calculated, and this difference was evaluated for statistical significance by a paired sample t test. RESULTS: Ninety-two ultrasound pairs were assessed, a sample size that provided .90 power to detect a gestational age estimate difference of 3 days between family practice and radiologist interpretations. The normally distributed observed mean difference in gestational age estimates was only 1.5 days. CONCLUSIONS: This study found no difference in gestational age assessment performed by closely supervised family practice residents in comparison to radiologists.

Biometry↗
PubMed2003

[Correlation between refraction and ocular biometry].

PURPOSE: To study the correlation between subjective refraction and biometry obtained by Orbscan and echography in normal eyes. To compare biometric parameters with the subjective spherical equivalent. MATERIAL AND METHODS: Subjective refraction, biometric parameters using Orbscan, and echography were recorded in 190 normal eyes (including eyes with ametropia) of 95 patients. Biometric parameters (i.e., corneal diameter, anterior chamber depth, central pachymetry, iridocorneal angle, corneal and lens radii of curvature, and axial length of the eye) were compared in different refractive groups and were correlated with the subjective refraction. RESULTS: Corneal biometric parameters did not correlate with the subjective spherical equivalent and showed no differences between the refractive groups except for the central pachymetry. In the high myopic group (<-6D), the central cornea was significantly thinner (531 micro m versus 549 micro m, p=0.016). The correlation between corneal radius and axial length was strong in emmetropic eyes (r(s)=0.63, p<0.001) and poor but significant in ametropic eyes (r(s)=0.28, p=0.002). Axial length, anterior chamber depth, and iridocorneal angle showed significant differences between the refractive groups (p<0.001) and correlated with the subjective spherical equivalent (r(s[[/INF=0.44, p<0.001). Subjective spherical equivalent showed the strongest correlation with the axial length (rs)=0.82, p<0.001). Subjective spherical equivalent, central corneal thickness, axial length, anterior chamber depth, and anterior corneal radius showed a strong correlation between both eyes (rs[[/INF=0.94, p<0.001). CONCLUSION: Biometric characteristics of the eye (excluding cornea characteristics) vary with subjective spherical equivalent. Axial length presents the strongest correlation with the subjective spherical equivalent and correlates with the other ocular biometric parameters. Axial length plays a major role in the ocular biometry and refraction.

Adult↗
PubMed2003

[Post-operatory biometry and refraction results estimated and refraction surprises--clinical study].

Preoperative biometry has a major influence on the success or failure of IOL implantation procedures. The paper wishes to demonstrate the significance of this manoeuvre for the refraction and visual outcome and for the postoperative satisfaction rate of the patients. The clinical study has rulled out for one year period and a number of 239 patients suffered a IOL implantation procedure (cataract or lens extraction for refractive purposes). The preoperative biometry was always necessary. We used one of the existing IOL power calculation formula (SRK II, SRK T, Holladay). The surgeon decided about the IOL power, always after discussing with the patient their postoperative refractive expectations. The postoperative refraction was, in the majority of cases, the estimated refraction and the errors were similar with those from the literature. Refractive surprises of several diopters were registered in high myopic and hyperopic eyes or in cases of coexisting ocular diseases which have modified the anatomical parameters of the eye. In conclusion, small errors in calculation can have large effects on visual outcome. This problem will be solved in the future, because the field is evolving rapidly driven by a new understanding of the anatomy of the eye and new hardware for measuring that anatomy.

Biometry↗