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PubMed1990

[The reliability of ultrasound biometry].

Preoperative ultrasonic biometry is indispensible in cataract surgery in order to calculate the power of the intraocular lens to be implanted. Various authors have suggested that the accuracy of the measurements could be improved by performing biometry several times and basing the calculation of the lens on the mean value. The problem of the retest reliability of ultrasonic measurements was investigated in 99 young subjects with healthy eyes and 60 cataract patients. Biometry was performed three times consecutively in each mode using three different scanners and different coupling techniques. A comparison of the consecutive measurements showed good agreement (between r = 0.96 and r = 0.99) in regard to axial length and hence very good retest reliability. The accuracy of the repeat measurements was approximately the same with all three coupling methods used. The correlation coefficients of retest measurements of anterior chamber depth and lens thickness were much lower (r = 0.78 to r = 0.96). This may be explained by differences in handling of the probes, in the test modes, and in the physical conditions on which the measurements are based. In view of the good reproducibility of axial length measurements the authors consider one carefully performed biometry more valuable for preoperative calculation of lens power than the mean of several measurements.

Adult↗
PubMed2004

[Comparison of ultrasound and optic biometry with respect to ocular refraction after cataract surgery].

In the prospective study of 56 patients with cataract (67 eyes) the authors compared axial length biometry) regarding to postoperative refraction of the eyes. Dioptric power of the intraocular lens (IOL) was determined by SRK II. formula. The difference between predicted and actual postoperative refraction in the spherical equivalent were compared 3 months postoperatively. Axial length measured by ultrasound differed significantly from the axial length measured by optical biometry (p = 0.016). Dioptric power of IOL calculated according to the axial length measured by ultrasound was significantly different from the dioptric power of IOL calculated according to the axial length measured by optical biometry (p = 0.003). The difference between predicted and actual postoperative refraction was not statistically significant (p = 0.384) even if we considered both type of measurement. In conclusion, we found partial coherence interferometry was an accurate and reproducible method for measurement of axial length of the eye before cataract surgery. In the cases of advanced dense cataracts backup of ultrasonic biometry is still necessary.

Cataract↗
PubMed1995

Gender-specific second-trimester biometry.

OBJECTIVE: This study was designed to evaluate the significance of gender differences for commonly used biometric parameters obtained ultrasonographically from second-trimester euploid fetuses. STUDY DESIGN: Gender-specific linear regression equations were developed for gestational age dependent and independent biometry from second-trimester ultrasonographically normal singleton euploid fetuses by use of biparietal diameters and femur and humerus lengths. Regression lines for male fetuses were compared with those for females by determining overlap of 95% confidence intervals at specific points. RESULTS: A total of 288 male fetuses (mean gestational age 16.7 +/- 1.0 weeks) and 251 female fetuses (mean gestational age 16.8 +/- 1.2 weeks) (not significant) were evaluated. Small statistically significant gender differences in fetal biometry were identified. The largest gender difference for gestational age-dependent parameters was a biparietal diameter difference of 1.15 mm at 21 weeks. The largest gender difference for gestational age-independent parameters was a femur length difference of 1.7 mm at a biparietal diameter of 50 mm. CONCLUSION: Statistically, but not clinically, significant gender differences of small magnitude exist for second-trimester fetal biometry, suggesting that gender-specific nomograms may be of limited value.

Biometry↗
PubMed1998

How accurate is fetal biometry in the assessment of fetal age?

OBJECTIVE: The purpose of the study was to assess the accuracy of fetal biometry in the midtrimester of pregnancy in the assignment of fetal age. STUDY DESIGN: A total of 152 singleton, 67 twin, and 19 triplet gestations resulting from in vitro fertilization with ultrasonographic fetal biometry from 14 to 22 weeks made up the study population. A gestational age prediction equation was derived from singletons with the use of stepwise linear regression. This equation was compared with 38 previously published equations and then applied to the twin and triplet populations. RESULTS: Head circumference was the best predictor of gestational age (random error [SD] 3.77 days). Addition of abdominal circumference and femur length to head circumference improved the accuracy of the dating equation (random error 3.35 days). Most dating formulas had systematic errors of <1 week. The systematic error was -0.32 day for averaging the singleton-based predictions for twins and -1.26 days for triplets. CONCLUSIONS: Gestational age assessment with the use of fetal biometry from 14 to 22 weeks is accurate for singleton, twin, and triplet gestations.

Abdomen↗
PubMed2000

Prenatal detection of a high-risk group for intrauterine growth restriction based on sonographic fetal biometry.

OBJECTIVE: This study was performed to evaluate the significance of sonographic fetal biometry in predicting low birth weight. METHOD: Five hundred and sixty-eight single-term pregnancies were analyzed. They were stratified into seven subgroups by birth weight deviation (BWD). Among the 568 pregnancies, 115 were revealed to be small-for-gestational-age (SGA) (birth weight less than mean -1.5 S. D.). When IUGR was suspected by routine sonographic fetal biometry, 'IUGR work-up' was carried out. The diagnostic performance of our screening method for the detection of SGA pregnancies in the general population was calculated. RESULT: The sensitivity, specificity, positive predictive value, negative predictive value and odds ratio of our screening method for the detection of SGA pregnancies in the general population were 73.0, 96.6, 83.2, 98.0% and 131.0, respectively. CONCLUSION: These data suggest that sonographic biometry is useful for the prenatal detection of high-risk cases of fetal growth restriction.

Biometry↗
PubMed2005

[Crystalline lens biometry using A-scan ultrasound and the Orbscan device].

PURPOSE: To analyze the lens biometry obtained by Orbscan and A-scan ultrasound in normal eyes. MATERIAL: and methods: The lens thickness obtained by A-scan ultrasound and the anterior curvature of the crystalline lens obtained by Orbscan were prospectively recorded in 280 normal eyes (including eyes with ametropia) of 140 patients (10-95 years of age). The correlation of lens biometry with the contralateral measure, patient age and sex, subjective refraction, and other ocular biometric parameters (anterior chamber depth, iridocorneal angle, corneal diameter, central pachymetry, pupil, corneal radii of curvature, and posterior segment length) was assessed. RESULTS: The lens anterior curvature showed no significant correlation in particular with the subjective spherical equivalent; however, the quality of this measure was poor: the reproducibility of the lens anterior curvature was low (the average difference between two successive Orbscan measurements was 14.4%). The correlation with the contralateral eye was poor (rs=0.55; p<0.001 versus rs=0.97; p<0.001 for lens thickness). Lens thickness showed the strongest correlation with the patient's age (rs=0.82; p<0.001); it increased by 0.26 mm per decade. Lens thickness correlated with anterior chamber depth (rs=-0.72; p<0.001) and iridocorneal angle (rs=-0.65; p<0.001). The last two parameters also correlated with age (rs=-0.68; p<0.001 and rs=-0.62; p<0.001, respectively). Anterior chamber depth and iridocorneal angle decreased by -0.21 mm and -1.7 degrees , respectively, per decade. CONCLUSION: Lens thickness is mainly influenced by age and correlates with the anterior chamber depth and the iridocorneal angle. The influence of aging on anterior segment biometry essentially consists in an increase in lens volume.

Adolescent↗
PubMed2001

Multicenter biometry study of 1 pair of eyes.

PURPOSE: To assess the accuracy of biometry for intraocular lens (IOL) power calculation. SETTING: Six ophthalmic surgery centers in Europe and 1 in the United States. METHODS: Biometry was done as if in preparation for cataract surgery in 2 eyes of the same person with 10 combinations of operator and instrument. Data analysis followed a standardized procedure to assess repeatability (within-center variability) and reproducibility (between-center variability) of the test methods. RESULTS: The reproducibility of the corneal radius measurement was 0.06 mm. The use of different keratometric indices made conversion to K-values less reliable. The repeatability of the axial length (AL) measurement of 0.30 mm and the reproducibility of 0.66 mm converted to a calculated IOL power of 0.75 diopter (D) and 1.65 D, respectively. Thus, this potential patient runs the risk of a refractive surprise of up to 1.10 D purely as a result of a measurement error within a center and up to 2.30 D if the patient goes to the worst-case center. CONCLUSIONS: The biometry results show that the measured corneal radius can be used with confidence. Reproducibility errors in AL determination require personalization of formula constants or correction at the source by proper calibration.

Biometry↗
PubMed2002

Accuracy and reproducibility of biometry using partial coherence interferometry.

PURPOSE: To determine whether partial coherence interferometry is comparable to standard contact ultrasonic biometry in accuracy, reproducibility, and ease of use. SETTING: Academic university practice. METHODS: In this prospective study, simultaneous biometry was performed in 91 consecutive patients (111 eyes) using partial coherence interferometry (IOLMaster, Zeiss Humphrey Systems) and ultrasonic biometry (I(3), Innovative Imaging, Inc.). The differences between the predicted spherical equivalent in diopters (D) and the actual results with both techniques were compared. RESULTS: The IOLMaster was significantly better in the mean absolute error (0.533 D +/- 0.589 [SD] versus 0.757 +/- 0.723 D; P = .012) and the percentage of eyes within +/-0.5 D (61.2% versus 42.3%; P = .003) and +/-1.0 D (87.4% versus 77.5%; P =.05) of the predicted refraction. CONCLUSION: The IOLMaster was more accurate and reproducible than the contact ultrasonographic technique.

Biometry↗
PubMed1997

Standardizing constants for ultrasonic biometry, keratometry, and intraocular lens power calculations.

PURPOSE: To provide a method and values that facilitate standardization of constants for ultrasonic biometry, keratometry, and intraocular lens (IOL) power calculations. SETTING: University of Texas Medical School, Houston, Texas, USA. METHODS: Keratometry and ultrasonic biometry provide the two measured input variables for the six variable vergence equations used to calculate the appropriate IOL power for a specific patient with a cataract. A review of the literature reflecting the past 156 years of research and development reveals the appropriate index of refraction to be used with the keratometer for net optical corneal power, the location of the principal planes of the cornea, the nominal value for retinal thickness, and the appropriate velocities for ultrasonic measurement of the axial length. The relationship of the thick IOL to the thin IOL is derived along with the physical location of the thick lens. Two methods are described that provide the best IOL constant to be used by a manufacturer to minimize the prediction error for a surgeon using the lens for the first time. The formulas for phakic IOLs and secondary piggyback IOLs are also derived and applied to methods described above for standard IOLs. RESULTS: Using a standardized net index of refraction of 4/3 for the cornea eliminates a variability of 0.56 diopter (D) in the predicted refraction. Using a standardized 1532 m/s velocity for axial length measurements and adding a value of 0.28 mm reduces the tolerance of axial length measurements to +/-0.03 mm for any length eye. The physical location of the thick IOL's secondary principal plane must be anterior to the thin lens equivalent by approximately the separation of the principal planes of the thick lens. For biconvex poly(methyl methacrylate) IOLs, the separation in the principal planes is approximately 0.10 mm. Using these relationships, the physical position of the thick lens within the eye can be used to confirm the lens constant for any IOL style. CONCLUSIONS: Standardizing the constants for keratometry, ultrasonic biometry, and IOL power calculations can significantly improve the predictability of refractive outcomes. Back-calculating and physically measuring the position of the lens within the eye can provide surgeons with an initial lens constant known to have a standard error of the mean of +/-0.05 mm (+/-0.10 D). Other parameters such as the cardinal points of a lens, the shape factor, the lens-haptic plane, and the center lens thickness would allow further refinement of IOL power calculations.

Adult↗
PubMed1991

The reproducibility of biometry and keratometry measurements.

Axial length and corneal curvature are entered into formulae to calculate intraocular lens power for cataract surgery and the absolute measurement of fundus structures such as neuroretinal rim area in glaucoma. The reproducibility (coefficient of variation, CV) of biometry and keratometry was investigated by taking five measurements of thirty phakic eyes. Although both techniques were found to be highly reproducible (CV less than 1%), keratometry was the more so. However, a clinically significant difference was noted between the first and the mean of five readings for both biometry (0.15 +/- 0.05 mm) and keratometry (0.05 +/- 0.03). Taken together, these errors would result in a postoperative refractive error of 0.65D using the SRK formula. Measurement errors were just as likely to occur with short or long eyes. Similar results were found when the analysis was performed on three measurements of both axial length and corneal curvatures. We recommend taking the average of three biometry and keratometry readings to improve the reliability of the techniques, and to increase the accuracy of calculating intraocular lens power and fundus structure dimensions.

Biometry↗
PubMed2002

Evaluation of the validity and reliability of A-scan ultrasound biometry with a single use disposable cover.

BACKGROUND: The UK Medical Devices Agency has suggested that ophthalmic practitioners should, where practicable and not compromising clinical outcome, restrict corneal contact devices to single patient use to minimise a remote theoretical risk of transmission of new variant Creutzfeldt-Jakob disease (vCJD). This study reports on a modified technique of ultrasound A-scan biometry that complies with the MDA recommendations. METHODS: The right eyes of 37 consecutive hospital patients had a series of biometry readings taken with a Humphrey 820 A-scan instrument with a plane wave transducer use d conventionally and with the addition of a disposable latex cover. RESULTS: Intrasessional repeatability of axial length measurements was similar for conventional readings--mean difference 0.027 mm, 95% confidence intervals (CI) +/- 0.44 mm and those taken with a disposable cover (0.028 mm, CI +/- 0.38). Intersessional repeatability was equivalent with (0.002 mm, CI +.- 0.51) and without a cover (0.03 mm, CI +/- 0.51). Readings with a cover were not significantly different from those without (paired t test; p >0.05), but tended to be greater (mean difference 0.085 mm, CI +/- 0.60). CONCLUSIONS: These findings suggest that corneal contact biometry with a disposable cover is a viable and theoretically safer alternative to the conventional technique.

Adult↗
PubMedDate not supplied

Intraoperative biometry for intraocular lens (IOL) power calculation at silicone oil removal.

PURPOSE: Cataract development is common following retinal detachment surgery that necessitates silicone oil injection. Intraocular lens (IOL) power calculation in the presence of silicone oil is challenging for many reasons. The authors evaluated the accuracy of intraoperative biometry during cataract surgery in silicone-filled eyes. METHODS: Twelve cases of cataract in eyes filled with silicone oil after retinal detachment surgery were included. Preoperatively, keratometric readings were documented. Intraoperative axial length was measured following removal of silicone oil using a sterile probe of the Nidek Echoscan US800 unit. IOL power calculation was computed using the SRK/T formula. This was followed by phacoemulsification and foldable lens implantation. Postoperative refraction allowed evaluation of the accuracy of intraoperative biometry. The predictability of three different formulas was also compared (Holladay, SRK/T, and SRK II). RESULTS: Seven men and five women with a mean age of 50.2 years were included in the study. The mean postoperative spherical equivalent using the described technique was 6.77 +/- 0.43 diopters. SRK/T and Holladay formula had the best predictability for high axial length eyes, whereas the three studied formulas showed no significant differences in predictability in eyes with normal axial length. CONCLUSIONS: Intraoperative biometry proved to have good predictability for the absolute postoperative refractive error in cataract surgery for eyes at the time of silicone oil removal. This predictability was accurate independent of axial length.

Adult↗
PubMed2001

[Correlations between ocular biometry and post-surgical refraction].

PURPOSE: To show the importance of ocular biometry in establishing the power of intraocular lens. MATERIAL AND METHOD: We studied 212 eyes operated in the University Eye Hospital from Cluj-Napoca by planned extracapsular extraction with intraocular lens implantation. Before operation there was performed ocular biometry, using SRK II formulas for calculation of intraocular lens. At 6 weeks after operation, we checked the ocular refraction by dioptronometry and we established the optical correction of the patients. RESULTS: The standard error was statistically significantly in all cases. In 84.19% of cases it was performed visual acuity with optimal correction over 0.7. CONCLUSION: The ocular biometry represents significant factor in obtaining a very good visual acuity after cataract operation.

Adolescent↗
PubMed2005

[Observational study about biometry in patients with cataract and synchisis scintillans].

PURPOSE: to report the difficulties in biometry in patients with cataract and synchysis scintillans and the way to avoid the biometrical errors in such patients. MATERIALS AND METHODS: Observational study on 4 patients (from 3 different surgeons) with cataract and synchysis scintillans. RESULTS: In two patients, the biometry obtained an increased IOL dioptrical value (+29D, and +28D, respectively) which proved to be wrong by not obtaining the planed emmetropia postoperatively. Instead, the postoperative refraction showed increased myopia (-9D and -6.5D spherical equivalent, respectively), and explantation with re-implantation was needed. The secondary implant was chosen based on the postoperative refraction and primary implant value (+20D, and +24D respectively). In other two cases, the biometrical error was avoided by manually selecting the real antero-posterior axis value, not the mean value calculated by the computer. This method proved to be correct by obtaining near-emmetropia postoperatively. CONCLUSIONS: The association between cataract and synchysis scintillans is frequent, and the presence of synchysis scintillans could be a cause of errors in biometry. The biometrical errors could be avoided by amending the method of measurement. These observations stress the necessity of ocular echography in the case of opaque ocular media.

Aged↗
PubMed2000

Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocular lens calculation according to Haigis.

BACKGROUND: The precision of intraocular lens (IOL) calculation is essentially determined by the accuracy of the measurement of axial length. In addition to classical ultrasound biometry, partial coherence interferometry serves as a new optical method for axial length determination. A functional prototype from Carl Zeiss Jena implementing this principle was compared with immersion ultrasound biometry in our laboratory. PATIENTS AND METHODS: In 108 patients attending the biometry laboratory for planning of cataract surgery, axial lengths were additionally measured optically. Whereas surgical decisions were based on ultrasound data, we used postoperative refraction measurements to calculate retrospectively what results would have been obtained if optical axial length data had been used for IOL calculation. For the translation of optical to geometrical lengths, five different conversion formulas were used, among them the relation which is built into the Zeiss IOL-Master. IOL calculation was carried out according to Haigis with and without optimization of constants. RESULTS: On the basis of ultrasound immersion data from our Grieshaber Biometric System (GBS), postoperative refraction after implantation of a Rayner IOL type 755 U was predicted correctly within +/- 1 D in 85.7% and within +/- 2 D in 99% of all cases. An analogous result was achieved with optical axial length data after suitable transformation of optical path lengths into geometrical distances. CONCLUSIONS: Partial coherence interferometry is a noncontact, user- and patient-friendly method for axial length determination and IOL planning with an accuracy comparable to that of high-precision immersion ultrasound.

Adult↗
PubMed2006

Ultrasound biometry in the diagnosis of amblyopia in keratoconus.

Here, we describe a case in which A-scan ultrasound biometry was used to differentially diagnose the cause of reduced vision in a patient with keratoconus. A patient with keratoconus presented with reduced visual acuity in one eye, not improvable above 6/18 with specialist keratoconus contact lens fitting. This monocular amblyopia was attributed to previous anisometropic ametropia by the use of ultrasound biometry. The report demonstrates the usefulness of ultrasound biometry in the detection of amblyopia in circumstances in which a previous assessment of amblyopia is not possible. This information will impact upon decisions made for the future clinical management in this case, especially if vision deteriorates so that a corneal graft is required.

Adult↗
PubMed1982

[Diagnosis of intra-uterine growth retardation by intensive ultra-sound biometry].

In a prospective study on 125 maternity patients with suspected intra-uterine growth retardation, simple ultrasound biometry (measuring of the distance) and intensive ultra-sound biometry (measurement of the circumference and the surface) were compared. Of 85 newborn born within two weeks following the biometry 34 newborn had intra-uterine growth retardation with a weight percentile smaller than 5, and 32 newborn were growth retarded with a percentile of 5-10. In 19 cases no growth retardation was found. (12 newborn in this group had a weight percentile 10-25). The measurement of the biparietal diameter was capable of diagnosing at the most 50% of the growth retardations (percentile under 5). The accuracy of the diagnosis of intra-uterine growth retardation increased to 85% with the thoraco-abdominal transverse diameter. The so-called borderline cases (percentile 5-10) were diagnosed with the bi-parietal diameter in 38 percent of the cases and by the transverse thoracic diameter in 41% of the cases. Measurement of the circumference of the head resulted in no better measurements than the bi-parietal diameter. The addition of the measurement of the thoracic circumference increased the diagnosis of severe fetal growth retardation (percentile under 5) to 90% and in borderline cases to 88%. The head thorax index and the ratio of head circumference and thoracic circumference increase in our investigation the accuracy of the diagnosis of intra-uterine fetal growth retardation substantially.

Female↗
PubMed1999

Fetal ultrasound biometry: 1. Head reference values.

OBJECTIVE: To create reliable reference ranges and calculate Z scores for fetal head ultrasound biometry using a large sample size which is evenly distributed from 12 to 42 weeks of pregnancy. DESIGN: A prospective, cross-sectional study. SETTING: Obstetric clinics (outpatient and delivery units) at the University Hospital of Zurich. SAMPLE: The study data were obtained from 6557 pregnant women. METHODS: Only the first ultrasound examination between 12 and 42 weeks of each fetus with exactly established gestational age was used for analysis. No exclusions were made on the grounds of small-for-date birthweight, prematurity or other events several weeks after the examination. Separate regression models were fitted to estimate the mean and standard deviation at each gestational age for each parameter. RESULTS: A total of 6217 fetal head biparietal diameters and 5510 occipito-frontal diameters were measured. Both head circumference and cephalic index were derived in 5462 cases where both biparietal diameter and occipito-frontal diameter could be measured on the same fetus. The centile charts, tables and regression formulae for biparietal and occipito-frontal diameters, head circumference and cephalic index are presented. An application to calculate Z scores was developed using Excel (Microsoft Corporation, USA) and macros are presented in detail in the Figure 8 footnote. The comparison of our charts with those of the two most recent studies revealed almost no differences in biparietal diameter centiles. In one publication, occipito-frontal diameter charts, and in another, head circumference charts were different from the current study. CONCLUSIONS: We have presented centile charts, tables and regression formulae for fetal head ultrasound biometry derived from a large and minimally selected sample size in a carefully designed cross-sectional study. Complete tables and regression formulae to calculate reference ranges and Z scores are presented for use in computer-aided evaluation of fetal ultrasound biometry.

Adult↗