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At least 145 records · Page 8Linked to original sources
PubMed2003

Dynamic accommodative changes in rhesus monkey eyes assessed with A-scan ultrasound biometry.

PURPOSE: Prior studies in humans measured time constants of biometric accommodative changes as a function of amplitude, and prior studies in monkeys used slit lamp videography to analyze dynamic lenticular accommodative movements. Neither of these studies related biometric changes to refractive changes. We wished to develop and test methodology to begin to test the hypothesis that ocular biometric changes are well correlated with accommodative refractive changes in rhesus monkeys. METHODS: Methodology is described to dynamically measure biometric accommodative changes with A-scan ultrasonography. Lens thickness, anterior chamber depth, and anterior segment length (anterior chamber depth plus lens thickness) were measured dynamically during Edinger-Westphal-stimulated accommodation in two eyes of one rhesus monkey. In addition, dynamic accommodative refractive changes were measured with infrared photorefraction. Functions were fit to the accommodative and disaccommodative responses to obtain time constants. Derivatives of these functions allow peak velocities to be determined for each amplitude. Dynamic changes in lens thickness and anterior chamber depth measured with A-scan biometry were compared with dynamic measures of accommodation using infrared photorefraction. RESULTS: Lens thickness and anterior segment length increase and anterior chamber depth decreases during accommodation. The biometric changes are well correlated with the accommodative optical changes. Peak velocities of accommodative changes in lens thickness and anterior chamber depth increase with amplitude and peak velocities for disaccommodation were higher than those for accommodation. CONCLUSIONS: Dynamic A-scan provides a method for dynamic analysis of the accommodative biometric changes during Edinger-Westphal-stimulated accommodation in monkeys, although the measurement resolution of this approach is limited.

Accommodation, Ocular↗
PubMed2002

The problems of biometry in combined silicone oil removal and cataract extraction: a clinical trial.

PURPOSE: To evaluate the problems and accuracy of biometry in eyes that have been operated on by silicone oil removal combined with cataract extraction with or without intraocular lens implantation. SUBJECTS AND METHODS: Twenty-nine consecutive cases that have been operated on for silicone oil removal and cataract, with or without intraocular lens implantation, were included in a prospective study. Axial length measurement was done in silicone oil-filled eyes after changing the sound speed in vitreous cavity to 987 m/sec. The SRKT formula was used for intraocular lens calculation. The cataract was removed by phacoemulsification through corneal section or phacofragmentation through the standard vitrectomy sclerotomy. Intraocular lens implantation was done either on the peripheral anterior capsule (single piece, PMMA) or in the bag (acrylic foldable three pieces). The final refraction after at least 3 months' follow-up was measured. The difference between the predicted and the actual refraction was evaluated. A control group of 30 consecutive cases (20 nonmyopic and 10 highly myopic) of cataract extraction and intraocular lens implantation in eyes not filled with silicone oil was included using the same evaluation methods. RESULTS: The mean deviation of the final from the predicted refraction was 1.87 +/- 2.11 diopters (range, +3.25 to -9 diopters). A total of 72.4% had a deviation of +/-2 diopters. The mean deviation in high myopia was 3.04 +/- 2.68 diopters (12 cases) (range, +/-1.75 to -9 diopters), while in nonmyopic patients, the mean deviation was 1.04 +/- 1.04 diopters (17 cases) (range, +3.25 to -3.25 diopters). The difference between highly myopic and nonmyopic eyes was statistically significant (P < 0.05). Most high errors occurred in highly myopic eyes. There was no statistical difference between the types of silicone oil (1000 versus 5000) or the mode of cataract extraction (phacoemulsification versus pars plana phacofragmentation). In the control group, the mean deviation in high myopia was 1.48 +/- 1.02 diopters (10 cases) (range, +/-0.5 to -3.5 diopters), while in nonmyopic patients, the mean deviation was 0.65 +/- 0.75 diopters (20 cases) (range, +2.75 to -1.75 diopters). The difference was statistically significant (P < 0.05). CONCLUSION: Intraocular lens calculation in silicone oil-filled eyes is accurate in eyes that are not highly myopic. Some highly myopic eyes with posterior staphyloma have great deviation. Unsuitable formula, artifacts, or large eyes beyond the machine range may be the cause of errors of deviation of refraction. Comparable results are obtained in eyes regardless of the type of silicone oil (1000 or 5000) and techniques of intraocular lens implantation (in the sulcus or in the bag).

Adult↗
PubMed2004

Fetal age assessment based on ultrasound head biometry and the effect of maternal and fetal factors.

BACKGROUND: Maternal height and weight have increased during the past 20 years, as has birthweight. The aim of the present study was to establish new reference charts for gestational age (GA) assessment using fetal biparietal diameter (BPD) and head circumference (HC), and to determine the effect of maternal and fetal factors on age assessment. METHODS: This was a prospective, cross-sectional study of 650 healthy women with regular menstrual periods and singleton uncomplicated pregnancies, recruited after written consent. BPD (outer-outer) and HC were measured at 10-24 weeks of gestation. We used regression analysis to construct mean curves and assess the effect of maternal and fetal factors on age assessment. RESULTS: BPD and HC were successfully measured in 642 participants. Using BPD and HC before 20 weeks, the new charts gave 3-8 days higher GA assessment than the charts presently in use, and <1 day difference compared to other recently established charts. Maternal age, multiparity, fetal gender, breech position and shape of fetal head affect GA estimation by 1-2 days when using BPD (p = 0.0001-0.02). Only maternal age and fetal gender affected GA estimation when using HC (</= 1 day, p = 0.001). CONCLUSIONS: Our new charts for assessing gestational age based on fetal head biometry are notably different from charts presently in use. Maternal and especially fetal factors affect gestational age assessment when using BPD, but less so for the HC method, which is suggested as the more robust method.

Adolescent↗
PubMed2005

Refractive error and ocular biometry in Jordanian adults.

The aim of this study was to establish the prevalence of refractive errors in Jordanian adults of working age, and to study the ocular biometric correlates of refractive error in this population. Refractive error and ocular biometry were measured in 1093 Jordanian adult subjects aged 17-40 years to determine the prevalence of refractive error, and explore structural correlations of ametropia. Refractive error was measured using a Grand-Seiko GR-3100K closed-view infrared autorefractor. Ocular component measurements were made using A-scan ultrasonography and autokeratometry. The prevalence of myopia [spherical equivalent refraction (SER) less than -0.50 DS] and hyperopia (SER greater than +0.50 DS) was 53.71 and 5.67% respectively; 40.62% of the sample was emmetropic (refraction between +0.50 D and -0.50 D inclusive in both principal meridians). The distribution of SER was found to show marked leptokurtosis, exhibiting a peak between plano and 1 D of myopia. Corneal radius, anterior chamber depth, crystalline lens thickness, vitreous chamber depth and axial length (AL) parameters were normally distributed in the population studied. AL to corneal curvature ratio was not normally distributed, and showed marked leptokurtosis. Linear regression analysis showed that AL correlated most closely with spherical equivalent refractive error. This study has established a database of refractive error prevalence and ocular biometric correlates of ametropia in a Middle Eastern population of working age.

Adolescent↗
PubMed2002

A new non-contact optical device for ocular biometry.

BACKGROUND: A new commercially available device (IOLMaster, Zeiss Instruments) provides high resolution non-contact measurements of axial length (using partial coherent interferometry), anterior chamber depth, and corneal radius (using image analysis). The study evaluates the validity and repeatability of these measurements and compares the findings with those obtained from instrumentation currently used in clinical practice. METHOD: Measurements were taken on 52 subjects (104 eyes) aged 18-40 years with a range of mean spherical refractive error from +7.0 D to -9.50 D. IOLMaster measurements of anterior chamber depth and axial length were compared with A-scan applanation ultrasonography (Storz Omega) and those for corneal radius with a Javal-Schiötz keratometer (Topcon) and an EyeSys corneal videokeratoscope. RESULTS: Axial length: the difference between IOLMaster and ultrasound measures was insignificant (0.02 (SD 0.32) mm, p = 0.47) with no bias across the range sampled (22.40-27.99 mm). Anterior chamber depth: significantly shorter depths than ultrasound were found with the IOLMaster (-0.06 (0.25) mm, p <0.02) with no bias across the range sampled (2.85-4.40 mm). Corneal radius: IOLMaster measurements matched more closely those of the keratometer than those of the videokeratoscope (mean difference -0.03 v -0.06 mm respectively), but were more variable (95% confidence 0.13 v 0.07 mm). The repeatability of all the above IOLMaster biometric measures was found to be of a high order with no significant bias across the measurement ranges sampled. CONCLUSIONS: The validity and repeatability of measurements provided by the IOLMaster will augment future studies in ocular biometry.

Adult↗
PubMed2004

Ocular biometry and refraction in Mongolian adults.

OBJECTIVE: To describe the variation in ocular biometry and its association with refraction in adult Mongolians. METHODS: The study included 1800 subjects, aged 40 years or more, who were selected in two Mongolian provinces-Hövsgöl and Omnögobi-to participate in this population survey. Axial length (AL) and its components, as well as noncycloplegic autorefraction and corneal power (CP), were measured. RESULTS: Of those selected, 1617 subjects (90.0%) were examined. Mean +/- SD of AL was 23.13 +/- 1.15 mm. There was a very small but significant increase in mean AL with age (0.05 mm per decade, P = 0.03). Autorefraction was performed on 620 of 675 subjects of those examined in Omnögobi. The age and gender standardized prevalences of myopia (< -0.5 D), emmetropia, hyperopia (> +0.5 D), astigmatism (< -0.5 D of cylinder) and anisometropia (>1.0 D difference between eyes) were 17.2%, 49.9%, 32.9%, 40.9%, and 10.7%, respectively. Prevalence of myopia showed no clear trend with increasing age, whereas hyperopia, astigmatism, and anisometropia all increased monotonically. Multiple regression models revealed that AL (P < 0.001) and VCD (P < 0.001) were the strongest determinants of refractive error. CONCLUSIONS: In this cross-sectional study of adult Mongolians, a much lower prevalence of myopia was found than in other East Asian populations studied to date. The mean AL differed little between age groups, in marked contrast to data on Chinese people.

Adult↗
PubMed2005

Refractive error, ocular biometry, and lens opalescence in an adult population: the Los Angeles Latino Eye Study.

PURPOSE: To characterize age- and gender-related differences in refractive error, ocular biometry, and lens opalescence (NOP) in a population-based sample of adult Latinos. Also assessed were the determinants of age-related refractive differences. METHODS: Participants in the Los Angeles Latino Eye Study (LALES), a population-based study of Latinos aged 40 years and more, underwent an ophthalmic examination, including ultrasonic measurements of axial length (AL), vitreous chamber depth (VCD), anterior chamber depth (ACD), lens thickness (LT), and noncycloplegic automated and subjective refraction. Corneal curvature/power (CP) was measured using an autorefractor. NOP was graded at the slit lamp by an ophthalmologist using the Lens Opacity Classification System II. Age- and gender-related differences were calculated. Multiple regression models were used to identify the determinants of age-related refractive differences. RESULTS: Of the 6357 LALES participants, 5588 phakic individuals with biometric data were included in this analysis. Older individuals had shallower ACDs, thicker lenses, more NOP, and more hyperopia compared to younger individuals (P < 0.001). There was no age-related difference in AL (P > or = 0.05). Women had significantly shorter AL, shallower ACD and VCD, than did men (P < or = 0.01). The strongest determinants of refractive error were AL (primarily VCD) and CP. NOP was a small but significant determinant of refractive error in older individuals. CONCLUSIONS: Age- and gender-related differences in ocular biometric, refractive error, and NOP measurements are present in adult Latinos. While the relative contribution of NOP in determining refractive error is small, it is greater in older persons compared to younger individuals.

Adult↗
PubMed2004

Sonographic biometry of the frontal lobe in normal and growth-restricted neonates.

Assessing the impact of restricted intrauterine growth on neonatal frontal lobe (FL) dimensions is important. We aimed to create a sonographic nomogram of FL dimensions in neonates at different gestational ages (GA) and evaluate the impact of small head circumference (HC) on FL dimensions. We conducted sonographic biometry of the FL at birth. We included 218 newborn infants born at GA of 24-43 wk: appropriate for GA and normal HC (n = 178), and small for GA and small HC (n = 23). Infants with a 5-min Apgar score <7, severe congenital malformations, or chromosomal abnormalities were excluded. Through a coronal ultrasound scan via the anterior fontanelle at the level where the most lateral point of the left Sylvian fissure was best demonstrated, we drew a triangle connecting the most lateral point of the Sylvian fissure, the corpus callosum, and the subcalvarian point of the interhemispheric fissure. We measured the three sides of the triangle, Sylvian-fontanellar distance, Sylvian-callosal distance, and fontanellar-callosal distance, and calculated the frontal triangular area. All four FL dimensions increased significantly between 24 and 43 wk of gestation in both appropriate for GA-normal HC and small for GA-small HC neonates, and were strongly correlated with HC and birth weight. Regression lines of GA against Sylvian-fontanellar distance, Sylvian-callosal distance, fontanellar-callosal distance, and frontal triangular area in the appropriate for GA-normal HC group differed significantly from those of the small for GA-small HC group (p < 0.05). Male neonates had significantly larger Sylvian-fontanellar and Sylvian-callosal distances than females (p < 0.01 and p < 0.015, respectively). In conclusion, FL measures increased significantly between 24 and 43 wk of gestation, and were strongly correlated with HC. We speculate that a sonographically small fetal HC implies growth restriction of the fetal FL.

Age Factors↗
PubMed1981

Ocular biometry of the cynomolgus monkey.

Eight cynomolgus monkeys underwent ocular biometry. Body weight = 3.04 +/- 0.59 kg; horizontal corneal diameter = 9.79 +/- 0.47 mm; anterior corneal curvature = 59.20 +/- 1.51 diopters at 90 degrees, 58.81 +/- 2.18 diopters at 180 degrees, 0.40 +/- 1.03 diopters at 90 degrees-180 degrees; anterior chamber depth = 2.79 +/- 0.27 mm; lens thickness = 3.18 +/- 0.15 mm; vitreous cavity length = 11.25 +/- 0.51 mm; total internal axial length = 17.16 +/- 0.69 mm. Most of the ocular parameters were correlated with body weight.

Animals↗
PubMed1997

A case-control study of biometry in healthy and cataractous Eritrean eyes.

The keratometry and axial length readings of healthy eyes (405 subjects) and cataractous eyes (63 subjects) from a sample of Tigrinians living in the Eritrean capital of Asmara were obtained. All subjects were at least 40 years of age. The mean keratometry reading for healthy eyes was 43.37 diopters (SD +/- 1.61), while that for cataractous eyes was 43.57 diopters (SD +/- 1.79). These values were not significantly different. Similarly, there was no significant difference in the mean ocular axial length for the two groups (healthy eyes; 23.03 mm, SD +/- 1.24: cataractous eyes; 23.34 mm, SD +/- 1.54). There was no correlation between age and the biometry readings of healthy eyes. Data from this study has been used to calculate a standard intraocular lens power for use by Eritrea's Blindness Prevention Programme during cataract surgery on this population (22 diopters at A constant 118.3). With this intraocular lens, 48% of patients will be within +/- 1D of emmetropia when left without spectacle correction; 73% will need a spectacle correction within +/- 2D to produce emmetropia.

Biometry↗
PubMed1997

Improved system for sonographic imaging and biometry of the cornea.

We developed a programmable motion system for high-frequency (50 MHz) ultrasonographic imaging of the cornea. The system permits a variety of scanning modes, including arc scans matched to the approximate radius of curvature of the cornea. This approach allows high-precision biometry (+ or - 2 microm) over a much larger region of the cornea than the 3 mm central zone obtainable with conventional rectilinear scanning. Using 60 degree wide meridional arc scans covering each clock-hour of a rabbit cornea, we obtained data over an 8 mm wide central zone and produced maps representing the thickness of the corneal epithelium.

Animals↗
PubMed2006

Early fetal echocardiography: heart biometry and visualization of cardiac structures between 10 and 15 weeks' gestation.

OBJECTIVE: The purpose of this prospective cross-sectional study was to compile normative data about biometry of the fetal heart and great vessels between 10 and 15 weeks in 123 normal singleton pregnancies. Additionally, we investigated the different methods and the optimal examination time of early fetal echocardiography. METHODS: The interrogated parameters included total heart diameter; heart area and circumference; right and left ventricular diameter; diameter, circumference, and area of the thorax; and diameter of the aorta and pulmonary trunk. Visualization of the 4-chamber view, 3-vessel view, origin and crossover of the great arteries, aortic arch, ductus arteriosus, superior and inferior venae cavae, and pulmonary veins was analyzed, and the success rates by transvaginal sonography (TVS) and transabdominal sonography (TAS) were calculated. RESULTS: Complete evaluation of the fetal heart was impossible at 10 weeks; the total success rate increased from 45% at 11 weeks to 90% between 12 and 14 weeks and 100% at 15 weeks. Between 10 and 13 weeks, TVS was superior to TAS. At 14 weeks, both methods were similar to each other, and at 15 weeks, TAS allowed adequate visualization of all structures. Linear regression analysis showed a significant correlation between the interrogated parameters and gestational age, crown-rump length, and biparietal diameter (P < .05). The ratio of right and left ventricular diameters and the ratio of pulmonary trunk and aortic diameters were constant. CONCLUSIONS: Early fetal heart evaluation by TVS or TAS or both is reasonable and feasible. Our normative data could be helpful for understanding the normal development of the fetal heart and great arteries and for detection of cardiac defects in early pregnancy.

Adult↗
PubMed2000

Charts of Thai fetal biometries: 4. Abdominal circumference.

A cross-sectional study was conducted in order to construct a new reference chart for Thai fetal abdominal circumference (AC). A total of 621 normal pregnant women between 12-41 weeks of gestation and their fetuses were recruited. Measurements were made once at a randomly assigned gestational age specifically for the purpose of this study only. Due to unfavorable fetal position in some cases, AC data were available in 615 measurements. Linear regression models were fitted separately to estimate the mean and standard deviation as functions of gestational age. Reference centiles were constructed from both equations, assuming the data were normally distributed. A new reference centiles for AC is presented and compared with previously published data. Our derived centiles were lower than those from Western studies which may partly be due to racial differences. This emphasizes the need to develop fetal biometries charts specifically for each region.

Abdomen↗
PubMed2001

Variations in ocular biometry in an adult Chinese population in Singapore: the Tanjong Pagar Survey.

PURPOSE: To describe the variation in ocular biometry in adult Chinese individuals in Singapore. METHODS: This study was a population-based, cross-sectional survey of adult Chinese persons aged 40 to 81 years residing in Tanjong Pagar district, Singapore. Axial ocular dimensions, including axial length (AL), anterior chamber depth (ACD), lens thickness (LT), and vitreous chamber depth (VCD) were measured using an A-scan ultrasound device. Corneal curvature (CC) and noncycloplegic refraction were measured with an autorefractor, with refraction further refined subjectively. Lens nuclear opacity (NO) was graded clinically using the modified Lens Opacity Classification System III (LOCS III) score. RESULTS: A total of 1717 subjects were eligible for the survey, of whom 1232 (71.8%) participated. Biometric and refraction data were available for 1004 (58.5%) phakic subjects. The AL, ACD, LT, VCD, CC, and LOCS III scores were 23.23 +/- 1.17 mm, 2.90 +/- 0.44 mm, 4.75 +/- 0.47 mm, 15.58 +/- 1.11 mm, 7.65 +/- 0.27 mm, and 3.2 +/- 0.9 (mean +/- SD), respectively. On average, people aged 40 to 49 years, when compared with those 70 to 81 years, had longer ALs (mean difference, +0.58 mm), deeper ACDs (+0.52 mm), longer VCDs (+0.72 mm), but thinner lenses (-0.70 mm) and less severe NO (-1.7 LOCS III score). CCs did not vary significantly with age. After controlling for age, women had shorter ALs and VCDs, shallower ACDs, but thicker lenses and steeper CCs than men. The variation in noncycloplegic refraction with age was nonlinear. Among people aged 40 to 59 years, a higher prevalence of hyperopia was seen in older compared with younger persons (on average, a difference of +1.3 D for every 10-year difference in age, P: < 0.001), explained principally by shorter AL (and VCD) in older persons. Among those 60 to 81 years, this pattern was not obvious (a difference of -0.03 D for every 10-year difference in age, P: = 0.12), as NO became an additional determinant of refraction, with greater degrees of NO in older person's driving refraction in the "minus" direction. CONCLUSIONS: Ocular dimensions vary with age and gender in adult Chinese persons in Singapore. The variation in noncycloplegic refraction in people 40 years and older may be explained by differences in axial lengths (principally vitreous chamber depths) between older and younger persons and, from 60 years onwards, differences in lens nuclear opacification as well.

Adult↗
PubMed2001

Ocular biometry in the subtypes of primary angle closure glaucoma in University Malaya Medical Centre.

Thirty-seven consecutive patients (41 eyes) diagnosed with primary angle closure glaucoma (PACG) attending the Glaucoma Clinic in University Malaya Medical Centre, over a period of 6 months were categorized into acute, subacute and chronic PACG from their clinical presentation. Each case was subjected to automated refraction, A-scan biometry for anterior chamber depth, axial length and lens thickness, keratometry and corneal diameter measurement. Calculations for the relative lens position and the lens thickness: axial length index were performed. The data collected was analysed by the nonparametric test (Kruskal-Wallis), one way analysis of variance (ANOVA), chi-square test, Spearman's nonparametric correlations and regression analysis. For controls 15 eyes from 15 normal subjects matched for age, sex, refractive error and race were chosen and subjected to the same examinations. Chronic PACG was the predominant subtype (53.6% of patients and 58.5% of eyes). The ocular biometric measurements of acute PACG eyes deviated most from normals in having the shallowest anterior chamber depth, shortest axial length, smallest corneal diameter, steepest corneal radius, thickest and most anteriorly situated lens, and the greatest lens thickness: axial length index. The subacute subtype was closest to normal and chronic PACG subtype fell in between in most of the biometric characteristics. These findings were not statistically significant. All PACG eyes as a group however showed statistically significant shallower anterior chamber depth (p < 0.05), and a more anterior relative lens position (p < 0.05) compared to normals.

Academic Medical Centers↗
PubMed2002

Height and its relationship to refraction and biometry parameters in Singapore Chinese children.

PURPOSE: To examine the association between the anthropometric measurements of height, weight, body mass index (BMI) and refraction and other ocular parameters in Singapore Chinese children. METHODS: In a cross-sectional study of 1449 Chinese schoolchildren, aged 7 to 9 years, from three Singapore schools, height and weight were measured according to standard protocol, and BMI was calculated. Refractive error and corneal curvature measures were determined by autorefraction in eyes under cycloplegia. Axial length, vitreous chamber depth, lens thickness, and anterior chamber depth were measured using A-scan biometry ultrasonography. RESULTS: In comparison with the children with height in the first quartile for a given age and gender, the eyeball length in children in the fourth quartile was 0.46 mm longer, the vitreous chamber depth 0.46 mm deeper, the corneal radius of curvature 0.10 mm greater (i.e., flatter), refraction more negative by 0.47 D (-0.76 D versus -0.29 D), and axial length-to-corneal curvature radius (AL-CR) ratio higher, after analyses controlling for age, gender, parental myopia, reading, school, and weight. The associations of height with refractive error and AL-CR ratio were significant in girls but not in boys. Heavier and more obese children had refractions that were more hyperopic (P = 0.01, P = 0.08), after analyses controlling for age, gender, parental myopia, reading, and school (height was also controlled for if weight was evaluated). This association was present in boys but not in girls. CONCLUSIONS: Controlling for age, gender, parental myopia, reading, school, and weight showed that taller Singapore Chinese children had eyes with longer axial lengths, deeper vitreous chambers, flatter corneas, and refractions that tended toward myopia. In multivariate analysis, eyes in children who were heavier or who had a higher BMI tended to have refractions that were more hyperopic, and eyes in heavier children had shorter vitreous chambers. Differences between the present results and a recent report in Singapore adults suggest either a cohort effect or a potential influence of systemic endocrine or metabolic factors during childhood on refractive development.

Biometry↗
PubMed2002

[Ocular biometry theory and practice].

The paper presents elements of eye biometry theory and practice as seen by a young resident, in his first years of practice as ophthalmologist. The paper refers to the current stage of IOL measurement technique. Also, challenges for the younger generation are presented, such as new formulas for the patients who have undergone refractive surgery, measurement solutions for the patients affected by cataract, whose vitreous was replaced by silicone, and last but not least, the proper approach as regards biometrical measurements for children.

Biometry↗
PubMed2003

[Difficult cases in biometry measurement].

A few problems have not yet been resolved concerning intraocular lens (IOL) power calculation in difficult cases. Patients can be divided into three groups: Group 1, patients with no previous ocular surgery but with unusual anatomy (staphyloma, high hyperopic eyes, etc.); Group 2, patients with previous surgery except refractive surgery; Group 3, patients with previous refractive surgery. Various techniques must be used to increase the accuracy of IOL calculation. B-mode biometry and optical coherence tomography are suitable tools to increase the accuracy of axial length measurement. Computerized videokeratography can be helpful. However, the most difficult cases seem to be those in Group 3.

Biometry↗