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At least 19 recordsLinked to original sources
PubMed2003

Laser interference biometry versus ultrasound biometry in certain clinical conditions.

PURPOSE: To compare laser interference biometry (LIB) with conventional ultrasound biometry in certain clinical conditions such as globe deformities, eccentric fixation, retinal detachment, macular edema or silicone oil-filled eyes. SETTING: Department of Ophthalmology, Würzburg University Eye Hospital, Germany. METHODS: We evaluated all patients who came to our university hospital for axial length measurement with our routine immersion biometry system (Grieshaber Biometry System) and compared the results with those obtained using the Zeiss IOLMaster of Carl Zeiss Jena, the commercially available LIB device. RESULTS: Selected case reports demonstrate the advantages and disadvantages of LIB. Advantages of LIB were found in patients with asymmetrically shaped globes, eccentric fixation, silicone oil-filled eyes and a fearful/nervous disposition. Disadvantages of the system were revealed in cases of retinal detachment, severe opacities along the visual axis and poor patient cooperation. CONCLUSION: We showed that LIB is a valuable addition to the choice of biometric devices, when used with medical understanding.

Aged↗
PubMed2003

Influence of operator experience on the performance of ultrasound biometry compared to optical biometry before cataract surgery.

PURPOSE: To compare measurements performed with the IOLMaster (Carl Zeiss, Meditec AG) with those obtained by applanation ultrasound (US) and manual keratometry and to evaluate the effect of operator experience on US biometry. SETTING: Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS: The axial length (696 eyes) and anterior chamber depth (ACD) (462 eyes) were measured in 377 patients with cataract using the IOLMaster and applanation US. To assess the effect of operator experience on the biometric results, the operators were divided into 2 groups: experienced and less experienced in performing US biometry. The difference in measurements between the methods and the variability of the difference were compared between the 2 groups. RESULTS: Applanation US measured axial length and ACD shorter than the IOLMaster; the mean numerical difference was 0.13 mm and 0.19 mm, respectively (P<.01). For axial length, the absolute difference was smaller with experienced operators than with less experienced operators (0.15 mm versus 0.22 mm) (P<.01). For ACD, experienced operators obtained a smaller difference between measurement techniques (0.21 mm versus 0.29 mm; P<.05). CONCLUSIONS: Experienced US operators had less difference and lower variability in the difference between applanation US and IOLMaster readings for axial length and ACD measurements. The noncontact optical method, which is essentially operator independent, gave significantly more reliable biometry before cataract surgery, especially in the case of less experienced operators.

Adult↗
PubMed2003

[First steps with the Zeiss IOLMaster: A comparison between acoustic contact biometry and non-contact optical biometry].

BACKGROUND: After having received an IOL-Master (Zeiss, Jena), we compared our actual standard method with this new device. PATIENTS, MATERIALS AND METHODS: From March to June 2002, we examined 175 consecutive cataractous eyes with the IOL-Master as well as with the acoustic biometry (Tomey AL-1000) combined to the Javal-Keratometer (Haag-Streit, Bern). The results were compared and analysed statistically. In all eyes, the intraocular lens to be implanted was chosen by means of the SRK/T formula, based on the measurements conducted with our standard method. The achieved postoperative refraction of 153 eyes obtained, at least six weeks after surgery, by the treating ophthalmologists, was communicated to us. RESULTS: Comparison of eye lengths as well as of the keratometric measurements showed good correspondence between the obtained measurements by both methods, acoustic biometry yielding significantly (p < 0.001) shorter axial lengths than the IOL-Master, and the Javal yielding significantly (p < 0.001) higher mean corneal refraction power than the IOL-Master. For both measurements, regression lines showed good coherence of the results over the refraction sample of our patients. Surprisingly, the accuracy of the refraction obtained postoperatively compared to the preoperative aim was better with our standard method compared to the IOL-Master. CONCLUSIONS: The predicted systemic differences in measurement results could be verified. No improvement in accuracy of our postoperative refraction prediction was achieved so far. The current advantage of the IOL-Master in our clinic is the substantial gain in time, as well as the fact that performance of the measurements may be delegated.

Adult↗
PubMed2003

The Doppler assessment in multiple pregnancy randomised controlled trial of ultrasound biometry versus umbilical artery Doppler ultrasound and biometry in twin pregnancy.

OBJECTIVE: To assess the addition value of umbilical artery Doppler ultrasound added to standard ultrasound biometry measurements in the management of twin pregnancies. DESIGN: A prospective randomised controlled multicentre trial of women with twin pregnancies. SETTING: Tertiary level referral hospitals in Australia, New Zealand and Southeast Asia. POPULATION: Pregnant women with twin pregnancies. METHODS: Women were randomised at 25 weeks of gestation to receive either standard ultrasound biometric assessment or standard assessment plus Doppler ultrasound umbilical artery flow velocity waveform analysis. The studies were repeated at 30 and 35 weeks unless otherwise indicated. Physicians were advised to institute close fetal surveillance in the presence of an abnormal umbilical artery Doppler study or with biometry indicators of fetal compromise. MAIN OUTCOME MEASURES: Standard obstetric (mode of delivery, perinatal mortality, hypertension, antenatal admissions and gestation at delivery) and neonatal (5 minute Apgar scores <5, admissions to neonatal nursery and requirements for ventilation) outcomes and statistical analysis was on intention-to-treat. There were no significant differences between the two groups with respect to demography, antenatal, peripartum and neonatal outcomes. There was no difference in the perinatal mortality rate in the no Doppler group (n = 264), which was 11/1000 live births, and the Doppler group (n = 262), which was 9/1000 live births. There were three unexplained intrauterine deaths in the no Doppler group and none in the Doppler group (OR 0.14, 95% CI 0.01-1.31). Two intrauterine deaths in the Doppler group were due to cord prolapse in labour and a fetomaternal haemorrhage, both very unlikely to be influenced by Doppler surveillance. CONCLUSIONS: In this study, close surveillance in twin pregnancy resulted in a lower than expected fetal mortality from 25 weeks of gestation in both the no Doppler and Doppler groups. The lower rate of unexplained fetal death in the no Doppler group was not significantly different from the Doppler group.

Adult↗
PubMed2001

[Optic biometry in intraocular lense calculation for cataract surgery. Comparison with usual methods].

PURPOSE: To compare axial length and intraocular lens power calculated from three biometry methods, then to study refractive postoperative results to assess the predictive value of each method. MATERIAL AND METHODS: This prospective study included 40 eyes planned for cataract surgery. Two skilled operators participated in this study: One for the surgery and the other for the biometry and measurement of intraocular lens power. For intraocular lens power, we used the optic biometer from Zeiss and the echograph B Ultrascan from Alcon. IOL power calculation was performed using the usual mathematical formulas based on 3 biometry methods. 1--keratometry measurement, anterior chamber depth (ACD), and axial length using optical biometry; 2--keratometry measurement using the Javal keratometer and biometry using the B mode ultrasonography; 3--keratometry measurement using the Javal keratometer and biometry using A mode ultrasonography. RESULTS: The average age of our patients was 69.5 years old, ranging from 52 to 81 years old. The average axial length was 23.46 mm with, ranging from 20 to 32.73 mm. The average keratometry with optic biometry was 43.97 diopters +/- 1.44 versus 43.84 diopters +/- 1.45 with the Javal keratometer. 40 eyes were examined and there were 4 failures (10%) for axial length measurement by optic biometry because the cataract was very dense. Biometric preoperative results with the 3 methods show that there was a statistically significant difference between the A mode and the B mode optic biometry (P < 0.006). On the other and, there was no statistical difference between optic biometry and the B mode. CONCLUSION: Optic biometry has a number of advantages. This is new method, is non invasive, easy to use, with no contact, and it is reliable. Results with this method are more precise than with ultrasonic biometry. For high myopia, optic biometry is a very valuable method. Its limits are total cataract and intraocular opacities; in these cases ultrasonic biometry is the best method.

Aged↗
PubMed2004

[Individual postoperative refraction after cataract surgery -- a comparison of optical and acoustical biometry].

BACKGROUND: Optical biometry with the IOL-Master is an innovative technique that claims to improve the refractive results of cataract surgery compared to acoustical biometry. METHODS: In 140 consecutive non-selected eyes prior to cataract surgery firstly an optical biometry (IOL-Master, Zeiss, V.2.02) and secondly an ultrasound biometry (Sonomed) were carried out. Cataract surgery was performed using either a PMMA-IOL (n = 56) or an acrylic IOL (n = 84). The PMMA-IOL's were implanted in the capsular bag via a scleral tunnel. The acrylic-IOL's were implanted via a clear cornea incision in the capsular bag. The length of the globe was analysed and the deviations between the postoperative refraction after 3 month and the preoperative planned refraction were compared. RESULTS: The mean axial length difference between optical biometry and acoustical biometry was 0.19 mm in the PMMA-lens group and 0.16 mm in the acrylic-lens group. The deviation of postoperative refraction (spherical mean) from the planned refraction was 0.46 +/- 0.88 D in the PMMA-IOL group and 0.25 +/- 0.77 D in the acrylic IOL group when biometry was performed by ultrasonography. When optical biometry was performed the respective values were 1.15 +/- 0.83 D in the PMMA-IOL group and 0.84 +/- 0.75 D in the acrylic IOL group. The differences in mean postoperative refraction of optical and acoustical biometry can be compensated by adaptation of the A constants. The standard deviation of the difference between the postoperative refraction and the preoperatively planned refraction - that means the individual deviations between postoperative refraction and preoperatively planned refraction - were almost identical in optical and acoustical biometry. CONCLUSION: Optical biometry represents a significant simplification in the course of investigation prior to cataract surgery. The claim of optical biometry, however, to gain a higher precision and thus a significantly better prediction of individual postoperative refraction after cataract surgery is not yet fulfilled.

Acrylates↗
PubMed1998

B-mode-guided vector-A-mode versus A-mode biometry to determine axial length and intraocular lens power.

PURPOSE: To compare prospectively the reproducibility and accuracy of B-mode-guided biometry with those of A-scan biometry using a conventional A-mode probe to calculate intraocular lens (IOL) power. SETTING: Department of Ophthalmology, Hôtel-Dieu de Paris, France. METHODS: The axial length (AL) in 87 eyes of 72 candidates for cataract surgery was determined by B-mode-guided vector-A-mode and A-mode biometry using an Ophthascan S Ultrasound imager. Patients were assigned to one of two groups based on the B-mode biometry: nonmyopic (AL < 24.5 mm; n = 54) or myopic (AL > 24.5 mm; n = 33). Postoperative refractive results were compared with attempted values. RESULTS: Mean AL variance was significantly greater when using the A-mode than the B-mode: 0.157 mm +/- 0.260 (SD) versus 0.015 +/- 0.018 mm in the myopic group (P < .001) and 0.024 +/- 0.024 +/- 0.045 versus 0.009 +/- 0.011 mm in the nonmyopic group (P < .001). More eyes having B-mode biometry achieved a final refraction within +/- 0.50 diopter (D) of the attempted refraction (63 and 43%, respectively; P < .05). No deviation greater than 1.60 D was observed with the B-mode in the myopic or nonmyopic group. Three cases with a such a deviation (up to 2.24 D) would have been observed had A-mode-based biometry been chosen for the IOL power calculation. In the myopic group, attempted postoperative refraction was within +/- 0.50 D in 78% of eyes having B-mode biometry compared with 65% having A-mode. This difference was not statistically significant. CONCLUSION> These results suggest that the reproducibility and accuracy of AL measurements are significantly better with B-mode-guided A-mode biometry than with A-mode biometry in myopic and nonmyopic eyes.

Biometry↗
PubMed2002

Partial coherence laser interferometry vs conventional ultrasound biometry in intraocular lens power calculations.

AIMS: The purpose of the study was to compare optical biometry based on partial coherence laser interferometry (PCLI) principle to conventional ultrasound biometry in the accuracy of intraocular lens (IOL) power calculations. The role of partial coherence laser interferometry in pseudophakic axial length measurement was analysed in the study. METHODS: In a prospective randomised clinical trial, 100 patients undergoing phacoemulsification cataract surgery were randomised to undergo biometry by either partial coherence laser interferometry (IOL Master) or the applanation ultrasound technique. The IOL material, design and the IOL formula were standardized. The mean error and mean absolute error were calculated and compared using paired t-tests. RESULTS: One hundred patients were included in this prospective randomised trial, of whom 50 patients underwent optical biometry and 50 patients had biometry by applanation ultrasound. The mean age of patients in the PCLI group was 67 +/- 6 yrs as compared to 71 +/- 8 yrs in the ultrasound group (P > 0.05). The preoperative mean axial length was 23.47 +/- 1.1 mm in the PCLI group (range 20-27.6 mm) and 23.43 +/- 1.2 mm in the ultrasound group with a range of 20.1-27 mm (P > 0.05). The mean absolute error (MAE) in the PCLI group was 0.52 +/- 0.32 D (upper and lower 95% CI 0.62 and 0.42 respectively). The MAE in the ultrasound group was 0.62 +/- 0.4 D (upper and lower CI 0.73 and 0.50 D respectively). Eighty-seven per cent of patients were within +/- 1 D in the PCLI group as compared to 80% in the ultrasound group (P = 0.24). The MAE of axial length difference with optical biometry was 0.13 mm +/- 0.13 SD (range -0.42 to 0.78 mm) in the PCLI group and 0.19 +/- 0.13 mm in the ultrasound group. There was a mean shortening of the eye length in the PCLI group postoperatively. Optical biometry improved the post op refraction by 16% on retrospective IOL power calculations. Eight per cent failed biometry with IOL Master (dense cataracts (4%) and fixation instability due to macular degeneration (4%)). CONCLUSION: The non contact optical biometry using the partial coherence laser interferometry principle improves the predictive value for postoperative refraction and is a reliable tool in the measurement of intraocular distances in pseudophakic eyes.

Adult↗
PubMed1998

Partial coherence interferometry: a novel approach to biometry in cataract surgery.

PURPOSE: To compare biometry performed by an enhanced version of dual beam partial coherence interferometry and applanation ultrasound in a prospective study of 85 cataract eyes to improve refractive outcome of cataract surgery due to a more accurate calculation of intraocular lens power. METHODS: The SRK II formula using ultrasound biometry data was employed. Three months after surgery, partial coherence interferometry biometry was repeated and refractive outcome was determined. Preoperative partial coherence interferometry biometry data were used to determine the refractive power of the intraocular lenses retrospectively and to calculate the possible refractive outcome. RESULTS: Precision of partial coherence interferometry biometry was more than 10 times better than that of ultrasound. Therefore, the possible mean absolute error for postoperative refraction achieved with partial coherence interferometry biometry was 0.49 diopters (compared with 0.67 diopters with ultrasound biometry), resulting in an improvement of 27%. Axial eye length measured with the two techniques differed by a mean of 460 microm. The difference in lens thickness measured with partial coherence interferometry and ultrasound significantly correlated with cataract grade. A mean shortening of 120 microm of axial eye length following cataract surgery was also detected by partial coherence interferometry. CONCLUSIONS: The enhanced version of partial coherence interferometry offers biometry with unprecedented precision (<10 microm) and resolution (approximately 12 microm), therefore improving the refractive outcome in cataract surgery. This noninvasive technique provides a high degree of comfort for the patient, with no need for local anesthesia or pupil dilation and minimized risk of corneal infection.

Adult↗
PubMed1991

Asteroid hyalosis and axial length measurement using automated biometry.

Accurate axial length measurements are needed before intraocular lens implantation in patients with asteroid hyalosis requiring cataract extraction. We suspected that falsely short axial length measurements may be obtained using automated A-scan biometry when we found an automated measurement of 15.90 mm in a patient with severe unilateral asteroid hyalosis. A manual biometry measurement of 21.90 mm was obtained for comparison; this was within 0.2 mm of the manual reading in the opposite uninvolved eye. A case-control study was performed on 20 unilateral asteroid hyalosis subjects using the uninvolved eye as the control, comparing automated biometry and manual A-scan biometry to assess the effect of asteroid hyalosis on automated biometry measurements. Five subjects (25%) with asteroid hyalosis had falsely short axial length measurements of more than 1.00 mm using automated biometry. This would result in more than 2.50 diopters of error in the implanted lens power. This case-control study demonstrates that falsely short axial length measurements may be obtained using automated biometry in patients with asteroid hyalosis, leading to significant error in intraocular lens power calculations.

Aged↗
PubMed2002

The evaluation of cardiac biometry in major cardiac defects detected in early pregnancy.

The objective was to evaluate early cardiac biometry in fetuses with structural cardiac defects between 10 and 17 weeks of gestation using our normative data about fetal heart biometry. A retrospective case series, patients were selected from all cases with congenital heart disease diagnosed between 10 and 17 weeks of gestation in our prenatal unit between 1999 and 2000. A schematic sonographic examination, including nuchal translucency (NT) thickness measurements, was performed and was followed by fetal Doppler echocardiography. The transversal heart diameter, both ventricular dimensions, heart area, heart circumference, thoracic diameter, thoracic circumference, thoracic area, pulmonary trunk diameter and aortic diameter were measured and the cardiothoracic ratios were calculated. Doppler evaluation of the umbilical arteries, ductus venosus and umbilical vein was performed. Fetal karyotyping was obtained by amniocentesis or chorionic villous sampling. During the study period, 31 cases of congenital heart disease between 10 and 17 weeks of gestation were diagnosed. Of these, two fetuses presented with ectopia cordis and six with insufficient cardiac biometric measurements. In the remaining 23 fetuses, different complex abnormalities with a high rate of chromosomal abnormalities (91%) were present. Fetal heart biometry was normal in 22% and abnormal in 78%. NT thickness measurements were performed before 14 weeks of gestation and ten of 12 fetuses (83%) presented with an increased NT. Both fetuses with normal NT showed an abnormal fetal heart biometry. Venous Doppler evaluation was performed in 22 cases and 12 fetuses (55%) demonstrated an abnormal venous Doppler. There were ten fetuses (45%) with normal venous Doppler; in seven of these cases, fetal heart biometry was partly abnormal. This study shows the feasibility of first and early second trimesters' fetal echocardiography and the applicability of cardiac biometry in these instances. In this context, early fetal heart biometry and NT thickness measurements may be complementary methods for the prenatal diagnosis of some major congenital heart defects. In early pregnancy, some cardiac defects like tricuspid valve dysplasia, coarctation of the aorta, aortic stenosis, tetralogy of Fallot or pulmonary stenosis may already show similar changes in the relation of the diameters of the fetal heart and great arteries, as seen in the second trimester. Therefore, evaluating the different cardiac ratios may have a high diagnostic value in early pregnancy.

Body Weights and Measures↗
PubMed2006

The AS biometry technique--a novel technique to aid accurate intraocular lens power calculation after corneal laser refractive surgery.

Intraocular lens power (IOL) calculation for cataract surgery has been shown to be inaccurate after photorefractive keratectomy (PRK), laser-assisted subepithelial keratectomy (LASEK) and laser in situ keratomileusis (LASIK). Many techniques exist to calculate corneal power with varying results and require the clinician to be aware of the pitfalls of IOL power calculation in post-refractive eyes. The AS biometry method proposed here is a simple method which does not rely on the calculation of corneal power. This new method is compared to the current gold standard the clinical history method (CHM). Twenty-nine eyes of 15 patients had routine biometry prior to LASIK, LASEK or PRK. The range of pre-operative spherical equivalent refractive error was -5.37 to +4.00 diopters. The post-operative refraction was measured at 3-6 months. The IOL power calculation was calculated using the AS biometry method and the CHM. The two methods were compared using the Student's paired t-test and the Bland Altman technique. There was no statistical difference between the AS biometry method and the CHM. The paired Student's t-test comparing the AS biometry method and the CHM showed no statistical difference, t=0.33 with a p-value of 0.75, at a 95% confidence interval. The authors conclude that the AS biometry technique is as accurate as the CHM. The former is a simpler method which avoids many of the pitfalls and confounding factors involved in IOL power calculation following corneal excimer laser surgery. However, like the CHM it requires measurements prior to laser surgery.

Adult↗
PubMed2003

Evaluation of the practicality of optical biometry and applanation ultrasound in 253 eyes.

PURPOSE: To evaluate the percentage of eyes that could not be measured using optical biometry and ultrasound applanation and the reasons. SETTING: Department of Ophthalmology, Johannes Gutenberg-University Hospital, Mainz, Germany. METHODS: Optical biometry (IOLMaster, Carl Zeiss Meditec AG) and A-scan ultrasound biometry were performed consecutively in 253 eyes scheduled for cataract surgery the next day. Lens opacities were evaluated with the Opacity Lensmeter (Interzeag), and a slitlamp examination and measurement of visual acuity were performed. The 2 techniques were compared in terms of the rate of and reasons for primary measurement failure. RESULTS: Measurement with the IOLMaster was not possible in 44 eyes (17%). Failed measurements were the result of a combination of low visual acuity and lens opacity in 45% of eyes, posterior subcapsular opacity in 25%, and macular disease in 7%. Measurement with ultrasound biometry was not possible in 10 eyes (4%); 7 eyes were filled with silicone oil and in 3 cases, the patient refused biometry. CONCLUSIONS: Optical biometry allowed comfortable, noncontact, high-precision measurement in the optical axis. Uncorrected visual acuity and lens opacity were predictors of successful measurements. Eyes with dense cataract or poor visual acuity are better evaluated using ultrasound applanation.

Adolescent↗
PubMed2006

National Biometry Audit II.

PURPOSE: To determine the change in compliance with the Royal College of Ophthalmologists biometry guidelines since the last National Audit 2 years ago and in particular to quantify the adoption of modern methods of axial length measurement and customization of A constants. METHOD: A structured telephone questionnaire of individuals who perform biometry in all eye departments in the United Kingdom. RESULTS: A biometrist was interviewed in 94 of the 178 United Kingdom Ophthalmology departments. Compared with 2 years ago, nurses alone perform biometry more frequently (67 vs 51%) and junior doctors less frequently (9 vs 15%). More biometrists now attend external training courses (45 vs 37%). The Royal College of Ophthalmologists recommended intraocular lens calculation formulae (SRK-T, Hoffer Q, and Holladay) are used more commonly (30 and 15%) and audit of prediction error is being performed more frequently (78 vs 71%). The routine use of a partial coherence laser interferometry has increased from 35 to 61% in United Kingdom Ophthalmology departments. Currently, only one United Kingdom department is routinely using immersion ultrasound biometry. 'A' constants are customized in 47% of departments. CONCLUSION: Over the last 2 years, there has been improved implementation of the Royal College of Ophthalmologists guidelines on biometry. It is essential that the Royal College of Ophthalmologists guidelines are updated to include current best practice of routine use of partial coherence laser interferometry or immersion biometry and customization of A constants. A benchmark standard of 85-90% of patients achieving a final postoperative refraction within 1 dioptre of the predicted should be established.

Biometry↗
PubMed2005

Optimization of biometry for intraocular lens implantation using the Zeiss IOLMaster.

PURPOSE: To compare the accuracy of biometry using conventional A-scan ultrasonography and partial coherence interferometry, and to improve the accuracy of biometry by sequential audit of postoperative refractive error. METHODS: The study was performed in three phases. In phase 1, 20 consecutive patients undergoing routine phacoemulsification underwent biometry using both A-scan ultrasonography and the Zeiss IOLMaster (ZIOLM). A single experienced optometrist refracted all patients 2 weeks after surgery. The errors between expected and achieved refraction were calculated and compared between the two methods. In phases 2 and 3, a further 22 and 20 patients, respectively, were recruited and only the ZIOLM was used for biometry. The manufacturer's suggested A-constant was refined and the error between expected and achieved refraction was calculated. RESULTS: In phase 1, the median unexpected error for the ZIOLM was+0.63 (interquartile range+0.368 to+1.015) and for A-scan biometry was --0.24 (interquartile range--1.335 to+0.802). In phase 1 65% of patients' postoperative refractions were found to be within 1.0 D of emmetropia using the ZIOLM (55% using A-scan biometry). Refinements to the A-constant improved this to 95% by phase 3. CONCLUSION: An error was identified in IOL power estimation with the ZIOLM, when using the manufacturer's recommended A-constant (recommended and previously optimized ultrasound A-constant 118.0; ZIOLM optimized A-constant 118.6). Serial modifications to the A-constant were successful in reducing the unexpected error to well within the tolerance limits of published international standards.

Adolescent↗
PubMed2005

Optimization of biometry for intraocular lens implantation using the Zeiss IOLMaster.

PURPOSE: To compare the accuracy of biometry using conventional A-scan ultrasonography and partial coherence interferometry, and to improve the accuracy of biometry by sequential audit of postoperative refractive error. METHODS: The study was performed in three phases. In phase 1, 20 consecutive patients undergoing routine phacoemulsification underwent biometry using both A-scan ultrasonography and the Zeiss IOLMaster (ZIOLM). A single experienced optometrist refracted all patients 2 weeks after surgery. The errors between expected and achieved refraction were calculated and compared between the two methods. In phases 2 and 3, a further 22 and 20 patients, respectively, were recruited and only the ZIOLM was used for biometry. The manufacturer's suggested A-constant was refined and the error between expected and achieved refraction was calculated. RESULTS: In phase 1, the median unexpected error for the ZIOLM was +0.63 (interquartile range +0.368 to +1.015) and for A-scan biometry was - 0.24 (interquartile range - 1.335 to +0.802). In phase 1 65% of patients' postoperative refractions were found to be within 1.0 D of emmetropia using the ZIOLM (55% using A-scan biometry). Refinements to the A-constant improved this to 95% by phase 3. CONCLUSION: An error was identified in IOL power estimation with the ZIOLM, when using the manufacturer's recommended A-constant (recommended and previously optimized ultrasound A-constant 118.0; ZIOLM optimized A-constant 118.6). Serial modifications to the A-constant were successful in reducing the unexpected error to well within the tolerance limits of published international standards.

Adolescent↗
PubMed1996

Adjusting the risk for trisomy 21 by a simple ultrasound method using fetal long-bone biometry.

OBJECTIVE: To establish the efficacy of second-trimester fetal long-bone biometry (femur, humerus, tibia, and fibula length) in detecting trisomy 21 and to generate tables for adjusting the risk of trisomy 21 according to long-bone biometry. METHODS: Four long-bones--femur, humerus, tibia, and fibula--were measured ultrasonically in singleton fetuses before genetic amniocentesis. Fetuses with normal karyotypes were used to derive regression equations describing predicted lengths on the basis of the biparietal diameter measurement. The efficacy of each abnormally short bone, alone and in combination, was determined in 22 fetuses with trisomy 21 encountered during the study period. After the sensitivity and specificity of long-bone biometry were established, appropriate tables were generated by Bayes' theorem to adjust the risk of trisomy 21 in the second trimester depending on long-bone biometry. RESULTS: Of 515 patients between 14 and 23 weeks' gestation, 493 had normal fetal karyotypes and 22 had trisomy 21. The sensitivity of an abnormal ultrasound, as defined by the presence of one or more short bones, was 63.6% and the specificity was 78.5%. According to Bayes' theorem, genetic amniocentesis may not be recommended for women less than 40 years old in the presence of normal long-bone biometry (ie, all four bones normal). CONCLUSION: Second-trimester fetal long-bone biometry is useful in detecting trisomy 21 and may be used to adjust the a priori risk of both high- and low-risk women for trisomy 21 and, therefore, the need for genetic amniocentesis.

Anthropometry↗
PubMed2004

Laser vs ultrasound biometry--a study of intra- and interobserver variability.

BACKGROUND: Accurate biometry is of vital importance in achieving predictable postoperative refraction following cataract surgery. AIM: To evaluate the accuracy and consistency in biometry, achieved by the new generation laser biometric system in comparison with the ultrasound biometric system. METHODS: The study was randomized and prospective. Biometry was performed in 68 eyes of 39 patients by three groups of biometrists (expert, intermediate user, novice). Expert and intermediate users are compared as group A, and expert and novice are compared in group B. Axial length, anterior chamber depth (ACD), and keratometry results are compared by t-test analysis. RESULTS: Axial length measurement variation between expert and non experts was 10 times less using laser than ultrasound (P<0.001). ACD measurement variation was also significantly less when using laser compared to ultrasound (P=0.003). Need for some level of user training is indicated in ACD measurement since group A achieved more consistent readings than group B. Keratometry measurements on the laser system were unreliable due to high range of results. Biometric failure was seen in 12% of eyes undergoing laser and 1% undergoing ultrasound biometry. CONCLUSION: Axial length determination by laser biometry is more accurate and consistent at all levels of biometrist expertise, compared to ultrasound biometry. ACD and keratometry measurements on the laser systems need some degree of user training in order to produce consistent results.

Adult↗