Anterior Segment Length Research Articles

Digital analysis of the human maxilla to enable semistandardized template tool reconstructions with free fibula transplants

ObjectivesThis study analyzed the human maxilla to support the development of mean-value-based cutting guide systems for maxillary reconstruction, bridging the gap between freehand techniques and virtual surgical planning (VSP).Materials and methodsThis retrospective cohort study used routine CT scans. DICOM data enabled 3D modelling and the maxilla was divided into four regions: paranasal (R1), facial maxillary sinus wall (R2), zygomatic bone (R3) and alveolar process (R4). Surface comparisons were made with a reference skull. Statistical analyses assessed anatomical variations, focusing on mean distance (Dmean), area of valid distance (AVD), integrated distance (ID) and integrated absolute distance (IAD). The study addressed hemimaxillectomy defects for two-segmental reconstructions using seven defined bilateral points to determine segmental distances and angles.ResultsData from 50 patients showed R2 as the most homogeneous and R4 as the most heterogeneous region. Significant age and gender differences were found in R3 and R4, with younger patients and females having more outliers. Cluster analysis indicated that males had R1 and R3 positioned anterior to the reference skull. The mean angle for segmental reconstruction was 131.24° ± 1.29°, with anterior segment length of 30.71 ± 0.57 mm and posterior length of 28.15 ± 0.86 mm.ConclusionsAnatomical analysis supported the development of semistandardized segmental resection approaches. Although gender and anatomical differences were noted, they did not significantly impact the feasibility of mean-value-based cutting-guide systems.Clinical relevanceThis study provides essential anatomical data for creating cost-effective and efficient reconstruction options for maxillary defects, potentially improving surgical outcomes and expanding reconstructive possibilities beyond current techniques.

Ocular Biometry Features and Their Relationship with Anterior and Posterior Segment Lengths among a Myopia Population in Northern China.

Objectives: The study aims to explore the ocular biometry of a myopic population in Northern China, focusing specifically on anterior and posterior segment lengths. Methods: This is a cross-sectional study. The medical records of 3458 myopic patients who underwent refractive surgery were evaluated. Axial length (AL), anterior chamber depth (ACD), lens thickness (LT) and other biometric parameters were measured using the IOL Master 700. The study determined the anterior segment length (ASL = ACD + LT), the posterior segment length (PSL = AL - ASL) and the ratio of ASL to PSL (ASL/PSL). Results: This study included 3458 eyes from 3458 myopic patients (1171 men and 2287 women). The mean age was 27.38 ± 6.88, ranging from 16 to 48 years old. The mean ASL was 7.35 ± 0.27 mm, and the mean PSL was 18.39 ± 1.18 mm. The ASL and PSL trends demonstrate an age-related increase for both genders, with notable gender-specific variations. Across most age groups, males typically exhibited higher ASLs and PSLs than females, with the exception of the 35-40 and 40-45 age groups. The ASL and PSL consistently increased with a rising AL. The AL strongly correlates with the PSL and negatively correlates with the ASL/PSL ratio. The ACD and LT moderately correlate with the ASL, but an increased LT does not imply a longer posterior segment. The CCT and SE show little correlation with axial eye parameters. Conclusions: Among Chinese myopic patients, a longer ASL and PSL were correlated with older age and the male gender. The AL strongly correlates positively with the PSL and negatively correlates with the ASL/PSL ratio. An elongation of the posterior segment may primarily account for an eyeball's lengthening.

The relationships between lens diameter and ocular biometric parameters: an ultrasound biomicroscopy-based study.

This study aims to explore the relationships between lens diameter (LD) measured with ultrasound biomicroscopy (UBM) and ocular biometric parameters. Ocular biometric parameters including axial length (AL), white-to-white distance (WTW), anterior chamber depth (ACD), lens thickness (LT) and anterior segment length (ASL) were measured with IOL-Master 700, and the direct measurement of LD was conducted through UBM (ArcScan Insight 100). Relationships between LD and ocular biometric parameters were then investigated. Eyes with AL ≥ 28 mm were defined as eyes with extreme myopia, and eyes with AL < 28 mm were defined as eyes without extreme myopia. A total of 194 eyes from 194 subjects were included. The mean LD was 9.58 ± 0.49 mm, ranging from 8.60 to 10.96 mm. According to univariate analysis, larger LD was associated with elder age, male gender, larger WTW, ACD and ASL (all p < 0.05). Meanwhile, the LD was positively correlated with AL in eyes without extreme myopia (p < 0.05), but not in eyes with extreme myopia (p > 0.05). Backward stepwise regressions revealed that a larger LD was associated with larger WTW, ASL and AL in eyes without extreme myopia (all p < 0.05), while ASL was the only significant variable in eyes with extreme myopia (p < 0.05). Larger WTW, ASL and AL in eyes without extreme myopia, as well as longer ASL in eyes with extreme myopia indicated a larger LD, which provides guidance in personalized surgical choice and promises ideal visual outcomes.

Three-dimensional Computed Tomography Scan of the Pelvic Bone in Isolated Epispadias: Analysis Before Surgical Correction

To determine intrapelvic angles and distances in pure epispadias patients and compare them to normal values. Using three-dimensional computed tomography, 17 intrapelvic dimensions (8 angles and 9 distances) were measured in 26 patients with pure epispadias (21 boys and 5 girls). These values were compared to normal values obtained from 6 patients (5 boys and 1 girl) who underwent either pelvic or abdominopelvic computed tomography for purposes unrelated to their bony pelvis. Significant differences were observed in five angles (sacroiliac joint angle, S1 tilt angle, sacral curvature, superior-inferior rotation of the pelvis, and pubococcygeal angle; P-value=.016, .044, .011, .020, and .001, respectively); these show less sacral rotation toward the axial plane, more sacral curvature, inferior rotation of the pelvis, and sacroiliac joints' rotation toward the coronal plane in epispadias compared to controls. Also, two distances (pubic diastasis and anterior segment length of the pelvis; P-value=.002 and .012, respectively) had significant differences, showing wider pubic diastasis and shorter anterior segment in epispadias. However, the differences between other intrapelvic angles and distances were not statistically significant between the two groups. In addition to the explanations hypothesized for the embryology of the exstrophy-epispadias complex, there can be other etiologies for both epispadias and bladder exstrophy to explain the differences between bony anatomies of the pelvis in these patients.

Comparisons of Using Cycloplegic Biometry Versus Non-cycloplegic Biometry in the Calculation of the Cycloplegic Refractive Lens Powers.

This study investigated the difference between the calculation of cycloplegic crystalline lens power (LP) using non-cycloplegic and cycloplegic biometry data in children, and associated factors were explored. A total of 821 children were enrolled and only right eye was analyzed. The corneal radii (CR), corneal power (CP), anterior chamber depth (ACD), lens thickness (LT), and axial length (AL) before and after cycloplegia were obtained using IOLMaster700. Anterior segment length (ASL) was defined as ACD plus LT. The cycloplegic LP was calculated with Bennett's formula. In addition, LP calculated with cycloplegic data was defined as cLP, otherwise it was defined as nLP. The ΔLP (defined as the value as cLP minus nLP) was compared among age, gender, and refractive states groups. Associated factors of ΔLP and |ΔLP| were explored by Pearson's correlation and multivariate linear regression. The mean age of the 821 subjects was 9.83 ± 2.97years with a mean spherical equivalent refraction (SER) of - 1.06 ± 2.12D. Overall, the ACD, LT, and ASL were significantly affected by cycloplegia agent (all p < 0.001; paired ttest). Conversely, no statistically significant differences were documented in AL, CP, or AL/CR ratio before and after inducing cycloplegia (p = 0.917, p = 0.515, and p = 0.549, respectively). Significant difference was found between nLP and cLP (21.24 ± 1.58D vs 21.43 ± 1.92D, p = 0.001). The mean ΔLP was 0.11 ± 0.87D (range from - 7.01D to 7.08D). Significant change in LP was found in low and medium groups, respectively (0.13 ± 0.81D, p = 0.001; 0.11 ± 0.48D, p = 0.043). In the multiple regression analysis, |ΔLP| was exclusively associated with ΔASL (β = 0.172, [95%CI 0.112-0.300], p < 0.001). Our results indicated that using cycloplegic biometry could lead to an overestimation in LP for low and moderate myopia eyes. This finding is likely to facilitate the refractive development research in children. ClinicalTrials.gov identifier, NCT05247099.

Axial Elongation During Short-Term Accommodation in Myopic and Nonmyopic Children.

PurposeAxial length increases during accommodation in adults and children; however, refractive error group differences are conflicting and have not been explored in pediatric populations. This study aimed to evaluate differences in accommodation-induced axial elongation between myopic and nonmyopic children.MethodsA range of ocular biometric measurements were captured during brief accommodation tasks (0, 3, 6, and 9 D) using a Badal optometer mounted to a noncontact optical biometer (Zeiss IOLMaster 700). Reliable measurements were captured for 15 myopic and 15 age- and sex-matched nonmyopic children. The average central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (LT), anterior segment length (ASL), vitreous chamber depth (VCD), and axial length (AL) were determined for each accommodation stimulus. Raw measurements of AL and VCD were corrected for the estimated error associated with LT increases during accommodation.ResultsAll biometric parameters, except CCT, changed significantly during accommodation (all P < 0.001). Myopic children exhibited significantly greater accommodation-induced axial elongation than nonmyopic children (P = 0.002) at the 3, 6, and 9 D accommodation stimuli, with a mean difference of 7, 10, and 16 µm, respectively (all pairwise comparisons, P ≤ 0.03). The changes in all other biometric parameters were not different between the refractive error groups (P ≥ 0.23).ConclusionsAccommodation-induced axial elongation was greater in myopic than nonmyopic children. This finding could support a potential mechanism linking near work, axial elongation, and myopia development in children or may reflect greater susceptibility to accommodation-induced axial elongation in children with established myopia.

An investigation into the total mandibular length and its potential correlation with the intraoral forces

ObjectivesIntraoral forces can be affected by several factors, including craniofacial dimensions, muscles, teeth status, and age. This study aims to reveal a possible correlation between maximum vertical interocclusal bite and masticatory forces and the total mandible length. Materials and methodsThe law of the lever was used to elucidate the mastication function by recording the occlusion and phases of mastication movements. A total of 115 people, 18 females, and 97 males, participated in the study. The midpoints of Gnathion (Gn), and Condyle (Co) were selected on the digital radiographs, and line connecting these points were used. Bite, and masticatory forces were measured in the anterior (intercanine) and posterior (premolar-molar) segments. Pearson correlation and multiple regression analyses were performed to evaluate the relationship between mandibular measurements and masticatory force. ResultsTotal mandible length varied between 11.0 and 13.0 cm in females and between 10.3 and 13.9 cm in males. The bite force of the anterior segment was found to be 34.2–52.1 kg in females and 27.0–61.2 kg in males, whereas posterior segment masticatory forces were determined between 45.0 and 69.0 kg in females and 36.8–93.6 kg in males. A weak positive correlation was found between the posterior segment and total mandibular length (p = 0.016) in the study. However, no correlation was found between the anterior segment and total mandibular length (p = 0.733). ConclusionThe results of the current study point to the fact that, as the total length of the mandible increase, the posterior segment masticatory forces increase as well. However, this relationship is relatively weak.

Associations between anterior segment parameters and rotational stability of a plate-haptic toric intraocular lens.

To evaluate the associations between anterior segment parameters and the rotational stability of a plate-haptic toric intraocular lens (IOL). Eye and Ear, Nose, Throat Hospital of Fudan University. Retrospective case series. Patients who underwent uneventful phacoemulsification and plate-haptic toric IOL (AT TORBI 709M IOL) implantation were included. Preoperative axial length (AL) and anterior segment parameters, including the white-to-white (WTW) distance, anterior chamber depth (ACD), lens thickness (LT), and anterior segment length (ASL; the sum of ACD and LT) were recorded. IOL rotation, residual astigmatism (RAS), and visual acuity were evaluated 1 month postoperatively. The associations between the anterior segment parameters and IOL rotation were evaluated. A total of 102 eyes of 102 patients were included. The mean AL was 26.43 ± 2.65 mm (range 21.71-34.60 mm). The mean IOL rotation was 4.59 ± 3.18 degrees, and RAS was 0.62 ± 0.39 D postoperatively. No correlation was detected between AL, ACD, or LT and the rotation of the plate-haptic toric IOL (all P > .05). However, its rotation correlated positively with the WTW distance (r = 0.250, P = .011) and ASL (r = 0.214, P = .030). Backward stepwise multiple linear regression revealed that the WTW distance (β = 2.142, P = .014) and ASL (β = 2.060, P = .037) were independent predictors of plate-haptic toric IOL rotation. Plate-haptic toric IOLs rotate more in eyes with larger WTW distances and longer ASLs; therefore, toric IOL implantation should be performed with caution in eyes with these characteristics.

Distribution of Ocular Anterior and Posterior Segment Lengths Among a Cataract Surgical Population in Shanghai.

Purpose: To investigate the distributions of the ocular anterior and posterior segment lengths among a cataract surgical population in Shanghai.Design: Cross-sectional study.Methods: Ocular biometric parameters of 23,462 eyes of 23,462 cataract surgery candidates were reviewed. Axial length (AL), anterior chamber depth (ACD), and lens thickness (LT) were obtained using IOL Master. Anterior segment length (ASL = ACD + LT), posterior segment length (PSL = AL – ASL) and the ratio of ASL to PSL (ASL/PSL) were calculated.Results: The mean ASL was 7.58 ± 0.39 mm, the mean PSL was 17.12 ± 2.64 mm. As the age grew, the ASL increased, and PSL increased firstly then decreased. Male subjects tended to have significantly longer ASL and shorter PSL than female subjects. With the increasing AL, the ASL was firstly decreased to trough at 20–22 mm AL group, then increased gradually, while the PSL increased rapidly. The ASL correlated positively with AL in normal, moderate and highly myopic eyes, negatively in short eyes. The PSL correlated positively with AL across the entire study population. The ASL/PSL was not constant in the eyes with different AL but had a relatively steep downward trend with the increasing AL in the short eyes, then decreased smoothly in normal, moderate and highly myopic eyes.Conclusions: In Chinese cataractous eyes, longer ASL and shorter PSL were associated with elder age and male gender. The change of ASL over AL was not linear, and the ASL was smallest in the eyes with AL of 20–22 mm. The elongation of the eyeball was mainly due to the extension of the posterior segment.

Cataract surgery and the small eye: relative anterior microphthalmos, high hyperopia and nanophthalmos

Relativer anteriorer Mikrophthalmus, hochgradige Hyperopie und Nanophthalmus bezeichnen klein gebaute Augen mit unterschiedlichem morphologischem Verhältnis zwischen Vorderabschnitt und Achsenlänge. Im Rahmen dieses Beitrags werden intraoperative Herausforderungen und chirurgische Lösungsansätze für die Kataraktoperation bei Patienten mit einer der 3 genannten morphologischen Veränderungen diskutiert. Zusätzlich wird auf mögliche, vorliegende Komorbiditäten, wie z. B. das Glaukom, und die präoperative Planung eingegangen.Video onlineDie Online-Version dieses Beitrags (10.1007/s00347-021-01483-5) enthält ein Video.

Role of the Pubic Symphysis in Osseous Pelvic Development: A Novel Model of Bladder Exstrophy in Rabbits.

It has been posited that the osseous pelvic anomalies seen in patients with classic bladder exstrophy (CBE) result from disruption of the pubic symphysis. This hypothesis, however, has not been tested. In the present animal study, our objective was to determine whether the tension of the pubic symphysis helps maintain the shape of the pelvic ring, or whether the growing bones maintain a ring shape even without the tension of the symphysis. In total, 12 neonatal New Zealand White rabbits underwent pubic symphysiotomy (experimental group, n=9) or sham surgery (control group, n=3) on days 3 or 4 of life. Rabbits were scanned with cone-beam computed tomography at 1, 4, 12, and 20 weeks postoperatively to monitor changes in the following pelvic parameters, which are known to be altered in CBE: anterior segment angle, anterior segment length, intertriradiate distance, interpubic distance, and posterior segment angle. Changes within the experimental and control groups were evaluated using repeated-measures analysis of variance and post hoc Tukey honest significant difference testing. Two-tailed t tests were used to compare treatment groups at each time point. Both groups showed increases in anterior segment length and intertriradiate distance during the study period; rabbits in the experimental group also showed a steady increase in interpubic distance (F=43.9; P<0.001). Experimental rabbits had significantly larger mean values for anterior segment angle, intertriradiate distance, interpubic distance, and posterior segment angle than did control rabbits at all time points. We found no difference in mean anterior segment length between control and experimental groups at any time point. The difference in interpubic distance was particularly pronounced by 20 weeks (experimental group, 13±2.7 mm; control group, 1.1±0.1 mm; P<0.001). The pubic symphysis is essential for normal pelvic development. Its absence led to early pelvic angulation and progressive pubic separation in a rabbit model. However, we found no significant difference in the mean anterior segment length, and it is likely that other factors are also implicated in the growth disturbance seen in CBE. Level V.

New IOL formula using anterior segment three-dimensional optical coherence tomography.

This retrospective study was aimed to compare prediction errors from various combinations of biometric data generated using optical coherence tomography (OCT) and develop a new intraocular lens (IOL) formula using biometric data. 145 eyes from 145 patients who underwent femtosecond laser-assisted cataract surgery (FLACS) were enrolled to the present study and they were divided into a training set (n = 92) and a test set (n = 53). Preoperative axial length (AL) and corneal radius were measured using partial coherence interferometry. The anterior chamber depth (ACD), lens meridian parameter (LMP), lens thickness (LT), thickness of anterior and posterior parts of the crystalline lens (aLT and pLT), and anterior segment length were measured by OCT. From a training set, we developed eight regression equations and analyzed the predictive accuracy. The regression equation using AL, LMP, and pLT (-1.143 + 0.148*AL + 0.428*LMP + 0.254*pLT) showed the strongest correlation with effective lens position (ELP) and smallest standard deviation of ELP prediction error. IOL formula generated using AL, LMP, and pLT yielded the highest predictive accuracy. In a test set, the new IOL formula also produced narrowest range of prediction error, smallest median absolute error, and highest percentages within ±0.25, ±0.50 than existing IOL formulas. The IOL formula considering AL, LMP and pLT will help to improve predictive accuracy in FLACS.

Changes in ocular biometry during short-term accommodation in children.

Near work has been linked with myopia development; however, the underlying mechanism remains unclear. Small increases in axial length during accommodation have previously been reported in adults, and therefore, this study aimed to examine if accommodation-induced changes in ocular biometry also occur in school-aged children. A range of ocular biometric measurements were captured during brief accommodation tasks at four demands (0, 3, 6, and 9 D), in a group of 87 non-myopic, school-aged children using a Badal optometer mounted to a non-contact optical biometer (Zeiss IOLMaster 700, https://www.zeiss.com/meditec/int/product-portfolio/optical-biometers/iolmaster-700.html). Reliable biometry measurements and active accommodation were observed for 76 participants who were included in the analysis. The average central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (LT), anterior segment length (ASL), vitreous chamber depth (VCD), and axial length (AL) were determined for each accommodation demand. Raw measurements of AL and VCD were corrected to account for the effect of LT changes during accommodation. On average, AL increased with increasing levels of accommodation (p=0.005). The mean (SEM, standard error of the mean) AL increase from 0 D to the 3, 6, and 9 D demands was 4 (1), 8 (1), and 15 (2) µm, respectively. All other biometric parameters, except CCT, changed significantly during accommodation. LT and ASL increased, and ACD and VCD decreased significantly with increasing accommodation (all p≤0.02). A longer baseline AL was associated with greater levels of accommodation-induced axial elongation at the 9 D demand (p<0.0001). AL increased significantly during accommodation in children, consistent with previous findings in adults up to a 6 D demand. AL continued to increase for higher levels of accommodation (9 D demand), which children may experience during near tasks. These findings provide further insights into potential mechanisms linking near work, axial elongation, and myopia development. However, no myopic children participated in this experiment; therefore, further research is required.

Preoperative biometric measurements with anterior segment optical coherence tomography and prediction of postoperative intraocular lens position.

The purpose of this study is to evaluate the biometric parameters of crystalline lens components and to find effective factors for predicting postoperative intraocular lens (IOL) position. This retrospective study included 97 eyes from 97 patients with a mean age of 63.00 ± 12.38 (SD) years. The biometric measurements were performed by means of a 3-dimensional optical coherence tomography (3D-OCT) device. Specifically, anterior chamber depth (ACD), aqueous depth (AD), lens thickness (LT), lens meridian parameter (LMP), white-to-white diameters (WTW), anterior segment length (ASL), the anterior part of lens (aLT), and the posterior part of lens (pLT) were measured. Additionally, axial length (AL) and corneal radius (CR) were measured by the partial coherence interferometry. Ninety-seven eyes were divided into thin lens group (LT < 4.5 mm) and thick lens group (LT ≥ 4.5 mm). The differences between the above two groups were also analyzed. Postoperative IOL position was measured by 3D-OCT at 3 months postoperatively and regression formulas for predicting postoperative IOL position were developed by various combinations of preoperative factors. As lens thickened, ACD and AD became shallow (all P < .001). AD, ACD, ASL, aLT, and pLT showed statistically significant differences between two subgroups classified on the basis of LT (all P < .001). Meanwhile, the value obtained by subtracting aLT from pLT did not show any association with the other biometric measurements. The combination of ACD, aLT, pLT, AL, CR, and WTW showed the highest correlation with postoperative IOL position (R2 = 0.536, P < .001). In conclusion, pLT–aLT was an independent factor not affected by any other variables and did not show significant difference between thin lens group and thick lens group. The subdivision of the lens structure using 3D-OCT helps to predict postoperative IOL position.

Morphometric analysis of the palatal shape and arch dimension in subjects with buccally displaced canine.

To analyse morphological variations of the palate shape and maxillary arch dimension between a group of subjects with unilaterally or bilaterally buccally impacted maxillary canines and a control group (CG) by means of 3D geometric morphometric (GMM). Pre-treatment records of 50 subjects (16 males and 34 females; mean age 13.9 years ± 1.8) with one or both canines buccally displaced were collected retrospectively. A CG of 50 subjects was selected from a list of orthodontic patients at the same dental hospital. The experimental group, buccally displaced canine (BDC) was divided in two groups: unilateral buccally displaced canine (UBDC) and bilateral buccally displaced canine (BBDC). To analyse the palate's shape and maxillary arch dimension, study casts were scanned. To study the entirety of the palatal shape, 3D GMM analysis was used. To analyse the maxillary arch dimension, the virtual three-dimensional models were measured with a specific software (VAM, Vectra, Canfield Scientific, Fairfield, New Jersey, USA). When comparing the groups with the GMM analysis, patients with BDC showed a statistically significant narrower and higher palatal vault. About the analysis of linear measurements, the intercanine width, the anterior and posterior segment length were significantly smaller in BDC, UBDC, and BBDC subjects when compared with the controls and there were no differences between UBDC versus BBDC groups. Patients with buccally displaced permanent canine tended to have maxillary transverse constriction and variation in palatal vault morphology. The morphometric variation of the palatine vault and arch dimensions can be considered a clinical factor associated with the presence of BDC.

Maxillary arch dimensions in the first 6months of life and their relationship with pacifier use.

This study evaluated the maxillary arch dimensions at birth and 6months of life, and to verify the influence of pacifier use on palatal development. Maxillary arch impressions were taken from 80 full-term newborns, appropriate for gestational age, from 24 to 72h of life, and repeated after 6months. Anatomical references were mapped on dental casts and measurements were taken. Parents were questioned about feeding practices and sucking habits. Data were analysed by Kruskal-Wallis test and hierarchical mixed regression model (p < 0.05). Anterior maxillary segment (median [interquartile range]) presented an increase in transverse (Δ% = 81.90 [74.40-89.70]) and in length (Δ% = 76.20 [49.10-102.70]) relative growth. No differences were detected in palatine depth from birth (11.00mm [10.30-11.70]) to 6months (12.60mm [12.0-13.90]). Pacifier use was positively related to the increase in anterior segment length. In the first 6months of life, the greatest relative growth of the maxillary arch occurs in the anterior region, showing this growth does not occur homogeneously. The use of pacifiers came to influence this process, even before the eruption of the upper incisors.

Effect of pupil dilation on biometric measurements and intraocular lens power calculations in schoolchildren.

PurposeTo investigate the effect of pupil dilation on ocular biometric parameters and intraocular lens (IOL) power calculation in schoolchildren using the Lenstar LS 900.MethodsOne hundred forty eyes of 140 healthy schoolchildren were included in the analysis. Axial length (AL), central corneal thickness (CCT), aqueous depth (AD), anterior chamber depth (ACD), lens thickness (LT), flat keratometry (K), steep K, astigmatism, white-to-white (WTW), and iris/pupil barycenter distance were measured, before and after pupil dilation. Anterior segment length (ASL) was defined as the sum of ACD and LT, and lens position (LP) was defined as ACD plus half of the LT. The relative lens position (RLP) was defined as LP divided by AL. IOL power was calculated using the eight formulas (Hill-RBF, Barrett, Haigis, Hoffer Q, Holladay, Olsen, SRK II, and SRK/T) integrated in the Lenstar LS 900. Parameters before and after pupil dilation were compared.ResultsAL, AD, ACD, LT, ASL, LP, RLP, flat K, iris barycenter distance, pupil barycenter distance, and PD differed significantly after pupil dilation (P < 0.001 in all cases), as compared to before dilation. The Olsen formula demonstrated significant differences in the magnitude of astigmatism (P = 0.010) and IOL power (P = 0.003) after pupil dilation. Using the different formulas, 23.6–40.7% of participants had IOL power changes of more than 0.50 diopters, while 0.7–1.4% had IOL changes of more than 1.0 diopter after pupil dilation.ConclusionsDilated and undilated pupil size affected the Lenstar LS 900 measurement of some ocular biometric parameters, and pupil dilation led to IOL power changes exceeding 0.50 diopters with a high percentage (from 23.6% to 40.7%) in schoolchildren, which should be noticed in clinical practice.

Optical Coherence Tomography Reveals Sigmoidal Crystalline Lens Changes during Accommodation.

This study aimed to quantify biometric modifications of the anterior segment (AS) during accommodation and to compare them against changes in both accommodative demand and response. Thirty adults, aged 18–25 years were rendered functionally emmetropic with contact lenses. AS optical coherence tomography (AS-OCT) images were captured along the 180° meridian (Visante, Zeiss Meditec, Jena, Germany) under stimulated accommodative demands (0–4 D). Images were analysed and lens thickness (LT) was measured, applying a refractive index correction of 1.00. Accommodative responses were also measured sequentially through a Badal optical system fitted to an autorefractor (Shin Nippon NVision-K 5001, Rexxam, Japan). Data were compared with Dubbelman schematic eye calculations. Significant changes occurred in LT, anterior chamber depth (ACD), lens centroid (i.e., ACD + LT/2), and AS length (ASL = ACD + LT) with accommodation (all p < 0.01). There was no significant change in CT with accommodation (p = 0.81). Measured CT, ACD, and lens centroid values were similar to Dubbelman modelled parameters, however AS-OCT overestimated LT and ASL. As expected, the accommodative response was less than the demand. Interestingly, up until approximately 1.5 D of response (2.0 D demand), the anterior crystalline lens surface appears to be the primary correlate. Beyond this point, the posterior lens surface moves posteriorly resulting in an over-all sigmoidal trajectory. he posterior crystalline lens surface demonstrates a sigmoidal response with increasing accommodative effort.

A retrospective study on the effect of long term orthokeratology on ocular biometry

Purpose: To investigate the effect orthokeratology (ortho-k) on changes in ocular biometry including central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (CLT), anterior segment length (ASL), vitreous chamber depth (VCD) and axial length (AL) compared to spectacle-wearing controls. The associations of these parameters and their changes with axial elongation were also investigated.

Morphometric analysis of the arteries of Willis Polygon

Abstract Objective: Willis polygon forms the basis of the arterial circulation of the cerebrum. Willis polygon is a vascular structure whom variations are not rare. Knowledge of the anatomy and preservation of its integrity is crucial for performing neurovascular surgery and intracranial tumour surgery. Because of the important vascular and neurological structures, approaches to this region are considered extremely risky. One of the main variations in-person basis is the diameter differences of the arteries, which forms Willis polygon, between the left and right hemispheres. About structure and variations, studies of Rhoton and Yasargil had formed the touchstone. Our aim is to contribute to the literature and clinical studies, to be done in the future, by comparing our results with previous studies about variations and morphometric features of Willis polygon. Methods: Arteries of 30 fresh cadaver brains were examined during autopsies in T.C. Ministry of Justice Istanbul Forensic Science Institute. Bilaterally anterior cerebral artery A1 segment lengths, distance between anterior communicating artery-callosomarginal artery outputs, posterior cerebral artery P1 segment lengths were measured using a digital calliper. After dissections and measures, photos of the region were taken and vascular anatomy and variations noted. From every single cerebrum samples were obtained from bilaterally A1, A2, callosomarginal artery, middle cerebral artery, posterior communicant artery, P1 and basilar artery. Samples were fixed by using 10% buffered-formalin. Taken samples were transported to Marmara University Faculty of Medicine, Department of Anatomy Laboratory. Samples were examined and interior diameters were measured under the microscope. Results: Our results with artery diameters and lengths were similar with literature. Different from literature, in anterior cerebral artery A1 segment, posterior cerebral artery P1 segment and posterior communicant artery no aplasia were noted. In 50% of the samples, callosomarginal artery were originate from A2 segment. In one case, we observed left and right pericallosal arteries were joined together at the end of the A2 segment and continued as a single pericallosal artery. We could not find any information about this variation in the literature. Conclusion: Before surgical operations, detailed knowledge of Willis polygon and evaluation of the pre-op cerebral angiography considering possible variations, reduce mortality and morbidity ratios. In addition, because of the role of flow gradients of Willis polygon in aneurysm formation, and in terms of better understanding the collateral circulation which is important in vascular occlusive diseases and vascular surgery, we believe, more anatomic studies about this region needed.