A nonlinear finite element model of the eye with experimental validation for the prediction of globe rupture

Effect of twisting of intravitreal injections on ocular bio-mechanics: a novel insight to ocular surgery

Although intravitreal (IVT) injections provide several advantages in treating posterior segment eye diseases, several associated challenges remain. The current study uses the finite element method (FEM) to highlight the effect of IVT needle rotation along the insertion axis on the reaction forces and deformation inside the eye. A comparison of the reaction forces at the eye's key locations has been made with and without rotation. In addition, a sensitivity analysis of various parameters, such as the needle's angular speed, insertion location, angle, gauge, shape, and intraocular pressure (IOP), has been carried out to delineate the individual parameter's effect on reaction forces during rotation. Results demonstrate that twisting the needle significantly reduces the reaction forces at the penetration location and throughout the needle travel length, resulting in quicker penetration. Moreover, ocular biomechanics are influenced by needle insertion location, angle, shape, size, and IOP. The reaction forces incurred by the patient may be reduced by using a bevel needle of the higher gauge when inserted close to the normal of the local scleral surface toward the orra serrata within the Pars Plana region. Results obtained from the current study can deepen the understanding of the twisting needle's interaction with the ocular tissue.

Evaluation of continuous curvilinear capsulorhexis based on a neural-network

PURPOSE

Continuous curvilinear capsulorhexis (CCC), as a prerequisite for successful cataract surgery, is one of the most important and difficult steps in phacoemulsification. In clinical practice, the size and circularity of the capsular tear and eccentricity with the lens are often employed as indicators to evaluate the effect of CCC.

METHODS

We present a neural network-based model to improve the efficiency and accuracy of evaluation for capsulorhexis results. The capsulorhexis results evaluation model consists of the detection network based on U-Net and the nonlinear fitter built from fully connected layers. The detection network is responsible for detecting the positions of the round capsular tear and lens margin, and the nonlinear fitter is utilized to fit the outputs of the detection network and to compute the capsulorhexis results evaluation indicators. We evaluate the proposed model on an artificial eye phantom and compare its performance with the medical evaluation method.

RESULTS

The experimental results show that the average detection error of the proposed evaluation model is within 0.04 mm. Compared with the medical method (the average detection error is 0.28 mm), the detection accuracy of the proposed evaluation model is more accurate and stable.

CONCLUSION

We propose a neural network-based capsulorhexis results evaluation model to improve the accuracy of evaluation for capsulorhexis results. The results of the evaluation experiments show that the proposed results evaluation model evaluates of the effect of capsulorhexis better than the medical evaluation method.

Discrepancy of eye injuries in mechanism, clinical features, and vision prognosis by different causative sports

Objective

To investigate the epidemiological and clinical characteristics of sports-related eye injuries in China, as well as how they differ depending on the sport or other specific factor that caused them.

Methods

Consecutive medical records from 2015 to 2019 of sports-related eye injuries from a standardized database in nine tertiary referral hospitals in China were retrospectively reviewed and analyzed.

Results

A total of 377 eyes in 376 inpatients (mean age, 22.5 ± 7.3 years; men:women 15.4:1) were included. Soccer (46.8%), basketball (27.1%), and badminton (16.8%) were the top three sports that caused injury. Ball strikes (74.7%), physical collision (13.8%), and racket/equipment beating (9.0%) were the common specific causes of injury. Blunt force injuries (95.8%) and close globe injuries (95.1%) accounted for the majority of injuries. Open globe injuries occurred more in basketball (8.3%) than in other sports, mainly due to physical collision (12.8%) and racket/equipment beating (11.8%). Basketball (13.4%) or physical collision (21.3%) caused Zone I injuries more frequently than other sports. Soccer (60.5%) and basketball (54.6%) caused more injuries to the posterior segment of the eyeball than other sports, mainly due to ball strikes (96.6%). Badminton (69.8%) and racket beating (61.8%) caused more Zone II globe injuries than other sports. In badminton, the percentage of hyphema (85.7%), the most typical symptom of eye damage, and ultimate visual acuity (VA) ≥20/40 (88.9%) was the greatest. A final low vision score of (≤4/200) was observed in 10.6% of all participants, including three participants who had an eye removed due to rupturing. The final VA was positively correlated with the presenting VA (r = 0.421).

Conclusion

Sports can lead to high proportions of ocular contusion injury and low vision. VA prognosis is closely related to initial VA following ocular sports trauma, which is directly determined by the causative sports and/or the specific causes. Effective eye protection is imperative to avoid or reduce visual impairments of sports participants.

Modelling and Development of a Mechanical Eye for the Evaluation of Robotic Systems for Surgery

Ophthalmic surgery, which addresses critical eye diseases such as retinal disorders, remains a formidable and arduous surgical pursuit. Nevertheless, with the advent of cutting-edge robotics and automation technology, significant advancement has been made in recent years to enhance the safety and efficacy of these procedures through meticulous research and development efforts. Ensuring the safe and effective execution of micro-surgical procedures requires stringent quality control measures, notably concerning evaluating and testing the devices utilized. During the development phase, these instruments must undergo extensive and continual evaluation by clinical practitioners to guarantee their safety and efficacy. Ideally, the test conditions should be identical to those of an actual operation. When testing robotic systems for ophthalmology, essential variables of the human eye, such as tissue properties and movement mechanisms, should be addressed. To minimize the discrepancy of tests and actual eye surgery conditions, in this paper, we propose a developed mechanical eye model to enable the realistic evaluation of ophthalmic surgical systems. After developing a virtual and physical model, the model was tested by an eye surgeon. The eye surgeon rated the model with four out of five possible points.Clinical relevance- This method ensures minimal discrepancy in verification of ophthalmic surgical devices by allowing the mechanical eye model to behave similar to the human eye, thus providing a realistic surgical procedure.

Ocular biomechanics during improvised explosive device blast: A computational study using eye-specific models

BACKGROUND

Eye injuries comprise 10-13% of civilian improvised explosive device (IED) injuries. The bomb blast wave induces a normal and shear forces on the tissues, causing a large acute IOP elevation. This study calculated the biomechanical stresses and strains in the eye due to IED explosion via eye-specific fluid-structure interaction (FSI) models.

METHODS

Blast occurred at 2, 3, and 4 m from the front and side of the victim and the weights of the IED were 1 and 2 kg. The ground was covered with the deformable soil to mimic the realistic IED explosion condition and reflect the blast wave.

RESULTS

The IOP elevation of ∼6,000-48,000 mmHg was observed in the eyes while the highest IOP was occurred with the IED weight and distance of 2 kg and 2 m (front) and the lowest was occurred with the IED weight and distance of 1 kg and 4 m (side). Our findings suggest the importance of the victim location and orientation concerning the blast wave when it comes to ocular injury assessment. IOP elevation of ∼2900 and ∼2700 mmHg were observed in ∼1.6 ms after the blast for the IEDS weight of 2 kg and a victim distance of 2 m in front and side blasts, respectively, in consistence with the literature. Nonetheless, IOPs were considerably higher after ∼1.6 ms due to the merging of the bomb blast wave and its reflection off the ground.

CONCLUSIONS

The stresses and strains were highest for the frontal blast. Both side and frontal blasts caused higher stresses and strains at the rectus muscle insertions where the sclera is thinnest and prone to rupture. Blast angle has no considerable role in the resultant IOP. Front blast with a heavier IED resulted a higher stresses and deformations in the eye connective tissues compared to the side blast.

Influence of the eye globe design on biomechanical analysis

PURPOSE

To assess the mechanical contribution of inner eye components on corneal deformation during a finite element analysis.

METHODS

A finite element model of an eye globe was implemented to examine the corneal response under various mechanical conditions. The model incorporates the cornea, limbus, sclera, iris, lens, muscles, anterior chamber and vitreous. The Ogden hyperelastic model was used for the corneo-limbal region and the Yeoh isotropic model for the sclera. The anterior chamber was modelled as a cavity and other eye components were incorporated as linear elastic material. A fluid dynamic simulation was implemented to determine the spatial air puff velocity and pressure profiles around corneal surface.

RESULTS

The maximal apical displacement under IOP = 15 mmHg was 0.22 mm with a stress of 0.013 MPa. An unrestrained limbus slightly increases the apical displacement, while an unrestrained equatorial sclera largely increases the displacement by 10%, resulting in reduced stiffness. The iris slightly decreases the displacement but increases stress in the corneal periphery. Meanwhile, the joint contribution of muscle and lens cannot be neglected as it reduces corneal displacement by 50%. Incorporation of the remaining eye components results in nearly similar results. Under air puff loading, a free equatorial sclera raised the dynamic deformation amplitude by nearly 2%, while the dynamic profile remained similar for all remaining study cases considered.

CONCLUSION

In a finite element analysis, the lens, iris, and muscle each provide major mechanical contributions to corneal deformation, and it is highly recommended that the internal contributions are considered.

The Biomechanics of Indirect Traumatic Optic Neuropathy Using a Computational Head Model With a Biofidelic Orbit

Indirect traumatic optic neuropathy (ITON) is an injury to the optic nerve due to head trauma and usually results in partial or complete loss of vision. In order to advance a mechanistic understanding of the injury to the optic nerve, we developed a head model with a biofidelic orbit. Head impacts were simulated under controlled conditions of impactor velocity. The locations of impact were varied to include frontal, lateral, and posterior parts of the head. Impact studies were conducted using two types of impactors that differed in their rigidity relative to the skull. The simulated results from both the impactors suggest that forehead impacts are those to which the optic nerve is most vulnerable. The mode and location of optic nerve injury is significantly different between the impacting conditions. Simulated results using a relatively rigid impactor (metal cylinder) suggest optic nerve injury initiates at the location of the intracranial end of the optic canal and spreads to the regions of the optic nerve in the vicinity of the optic canal. In this case, the deformation of the skull at the optic canal, resulting in deformation of the optic nerve, was the primary mode of injury. On the other hand, simulated results using a relatively compliant impactor (soccer ball) suggest that primary mode of injury comes from the brain tugging upon the optic nerve (from where it is affixed to the intracranial end of the optic canal) during coup countercoup motion of the brain. This study represents the first published effort to employ a biofidelic simulation of the full length of the optic nerve in which the orbit is integrated within the whole head.

Factors Affecting Child Injury Risk in Motor-Vehicle Crashes

Current recommendations for restraining child occupants are based on biomechanical testing and data from national and international field studies primarily conducted prior to 2011. We hypothesized that analysis to identify factors associated with pediatric injury in motor-vehicle crashes using a national database of more recent police-reported crashes in the United States involving children under age 13 where type of child restraint system (CRS) is recorded would support previous recommendations. Weighted data were extracted from the National Automotive Sampling System General Estimates System (NASS-GES) for crash years 2010 to 2015. Injury outcomes were grouped as CO (possible and no injury) or KAB (killed, incapacitating injury, nonincapacitating injury). Restraint was characterized as optimal, suboptimal, or unrestrained based on current best practice recommendations. Analysis used survey methods to identify factors associated with injury. Factors with significant effect on pediatric injury risk include restraint type, child age, driver injury, driver alcohol use, seating position, and crash direction. Compared to children using optimal restraint, unrestrained children have 4.9 (13-year-old) to 5.6 (< 1-year-old) times higher odds of injury, while suboptimally restrained children have 1.1 (13-year-old) to 1.9 (< 1-year-old) times higher odds of injury. As indicated by the differences in odds ratios, effects of restraint type attenuate with age. Results support current best practice recommendations to use each stage of child restraint (rear-facing CRS, forward-facing harnessed CRS, belt-positioning booster seat, lap and shoulder belt) as long as possible before switching to the next step.

Indirect Traumatic Optic Neuropathy Induced by Primary Blast: A Fluid–Structure Interaction Study

Current knowledge of traumatic ocular injury is still limited as most studies have focused on the ocular injuries that happened at the anterior part of the eye, whereas the damage to the optic nerve known as traumatic optic neuropathy (TON) is poorly understood. The goal of this study is to understand the mechanism of the TON following the primary blast through a fluid–structure interaction model. An axisymmetric three-dimensional (3D) eye model with detailed orbital components was developed to capture the dynamics of the eye under the blast wave. Our numerical results demonstrated a transient pressure elevation in both vitreous and cerebrospinal fluid (CSF). A high strain rate over 100 s−1 was observed throughout the optic nerve during the blast with the most vulnerable part located at the intracanalicular region. The optic nerve deforming at such a high strain rate may account for the axonal damage and vision loss in patients subjected to the primary blast. The results from this work would enhance the understanding of indirect TON and provide guidance in the design of protective eyewear against such injury.

Mechanical Evaluation of Retinal Damage Associated With Blunt Craniomaxillofacial Trauma: A Simulation Analysis

PURPOSE

To evaluate retinal damage as the result of craniomaxillofacial trauma and explain its pathogenic mechanism using finite element (FE) simulation.

METHODS

Computed tomography (CT) images of an adult man were obtained to construct a FE skull model. A FE skin model was built to cover the outer surface of the skull model. A previously validated FE right eye model was symmetrically copied to create a FE left eye model, and both eye models were assembled to the skull model. An orbital fat model was developed to fill the space between the eye models and the skull model. Simulations of a ball-shaped object striking the frontal bone, temporal bone, brow, and cheekbones were performed, and the resulting absorption of the impact energy, intraocular pressure (IOP), and strains on the macula and ora serrata were analyzed to evaluate retinal injuries.

RESULTS

Strain was concentrated in the macular regions (0.18 in average) of both eyes when the frontal bone was struck. The peak strain on the macula of the struck-side eye was higher than that of the other eye (>100%) when the temporal bone was struck, whereas there was little difference (<10%) between the two eyes when the brow and cheekbones were struck. Correlation analysis showed that the retinal strain time histories were highly correlated with the IOP time histories (r > 0.8 and P = 0.000 in all simulation cases).

CONCLUSIONS

The risk of retinal damage is variable in craniomaxillofacial trauma depending on the struck region, and the damage is highly related to IOP variation caused by indirect blunt eye trauma.

TRANSLATIONAL RELEVANCE

This finite element eye model allows us to evaluate and understand the indirect ocular injury mechanisms in craniomaxillofacial trauma for better clinical diagnosis and treatment.

[Intravitreal injection as a possible model for studying biomechanics of fibrous tunic]

The article summarized the results of Russian and foreign research concerning biomechnical principles of eye functioning as an integral physiological system. Quite a number of studies have been published on corneal and scleral mechanics, which is also part of the said system. These studies fall largely into three groups: in vivo studies (involving living organism), in vitro studies (within an artificial environment), and mathematical modeling. In vivo techniques are often rather complicated and, therefore, most studies are based on in vitro procedures. Due to the growing number of intravitreal injections, they can be regarded as a stress test for studying fibrous tunic biomechanics in vivo. The results of such studies would contribute to a better understanding of the pathogenesis of various eye diseases and thus, a better clinical practice.

Risk functions for human and porcine eye rupture based on projectile characteristics of blunt objects

Eye ruptures are among the most devastating eye injuries and can occur in automobile crashes, sporting impacts, and military events, where blunt projectile impacts to the eye can be encountered. The purpose of this study was to develop injury risk functions for globe rupture of both human and porcine eyes from blunt projectile impacts. This study was completed in two parts by combining published eye experiments with new test data. In the first part, data from 57 eye impact tests that were reported in the literature were analyzed. Projectile characteristics such as mass, cross-sectional area, and velocity, as well as injury outcome were noted for all tests. Data were sorted by species type and areas were identified where a paucity of data existed, based on the kinetic and normalized energy of assaulting objects. For the second part, a total of 126 projectile tests were performed on human and porcine eyes. Projectiles used for these tests included blunt aluminum projectiles, BBs, foam pellets, Airsoft pellets, and paintballs. Data for each projectile were recorded prior to testing and high-speed video was used to determine projectile velocity prior to striking the eye. In part three the data were pooled for a total of 183 eye impact tests, 83 human and 100 porcine, and were analyzed to develop the injury risk criteria. Binary logistic regression was used to develop injury risk functions based on kinetic and normalized energy. Probit analysis was used to estimate confidence intervals for the injury risk functions. Porcine eyes were found to be significantly stronger than human eyes in resisting globe rupture (p=0.01). For porcine eyes a 50% risk of globe rupture was found to be 71,145 J/m2, with a confidence interval of 63,245 J/m2 to 80,390 J/m2. Human eyes were found to have a 50% risk of globe rupture at a lower, 35,519 J/m2, with confidence intervals of 32,018 J/m2 to 40,641 J/m2. The results presented in this paper are useful in estimating the risk of globe rupture when projectile parameters are known, or can be used to validate computational eye models.

Development of numerical models for injury biomechanics research: a review of 50 years of publications in the Stapp Car Crash Conference

Numerical analyses frequently accompany experimental investigations that study injury biomechanics and improvements in automotive safety. Limited by computational speed, earlier mathematical models tended to simplify the system under study so that a set of differential equations could be written and solved. Advances in computing technology and analysis software have enabled the development of many sophisticated models that have the potential to provide a more comprehensive understanding of human impact response, injury mechanisms, and tolerance. In this article, 50 years of publications on numerical modeling published in the Stapp Car Crash Conference Proceedings and Journal were reviewed. These models were based on: (a) author-developed equations and software, (b) public and commercially available programs to solve rigid body dynamic models (such as MVMA2D, CAL3D or ATB, and MADYMO), and (c) finite element models. A clear trend that can be observed is the increasing use of the finite element method for model development. A review of these modeling papers clearly indicates the progression of the state-of-the-art in computational methods and technologies in injury biomechanics.

Development of a finite element-based injury metric for pulmonary contusion part I: model development and validation

Pulmonary contusion is the most commonly identified thoracic soft tissue injury in an automobile crash and after blunt chest trauma and affects 10-17% of all trauma admissions. The mortality associated with pulmonary contusions is significant and is estimated to be 10-25%. Thus, there is a need to develop a finite element model based injury metric for pulmonary contusion for the purpose of predicting outcome. This will enable current and future finite element models of the lung to incorporate an understanding of how stress and strain may be related to contusion injuries. This study utilizes 14 impacts onto male Sprague-Dawley rats. In 5 of these tests, a calibrated weight (46 g) is dropped from a height of 44 cm directly onto the lungs of intubated, anesthetized rats in situ. Contused volume is estimated from MicroPET scans of the lung and normalized on the basis of liver uptake of 18F-FDG. The lungs are scanned at 24 hours, 7 days, and 28 days (15 scans), and the contused volume is measured. In addition, 9 controlled mechanical tests on in situ rat lung are used for model development and validation. Identical impacts are performed on a finite element model of the rat lung. The finite element model is developed from CT scans of normal rat and scaled to represent average rat lung volume. First principal strain is chosen as a candidate injury metric for pulmonary contusion. The volume of contused tissue at the three time points measured using PET is compared to the strain level achieved by a corresponding volume in the finite element model. For PET scans (n=5 scans per time point), the average contusion volume was 4.2 cm3 at 24 hours, 2.8 cm3 at 7 days, and 0.39 cm3 at 28 days. These volumes were used to identify threshold peak first principal strain levels measured by the finite element model. Maximum first principal strain from the finite element model for the three volume levels (4.2, 2.8, and 0.39 cm3) was 3.5%, 8.8%, and 35% strain, respectively. Furthermore, the lung model exhibited exponential decay in principal strain threshold as more of the lung volume was considered, correlating to the precise and well defined volume of the contusion as it healed. The results of this study may be used to establish an injury metric to predict pulmonary contusion due to an impact to the lungs. The results may be used to improve finite element models of the human body, which may then be used to tune stiffnesses of interior components of automobiles and tune safety systems for maximum mitigation of this serious injury.

The effects of depowered airbags on eye injuries in frontal automobile crashes

The purpose of this study was to investigate eye injuries resulting from frontal automobile crashes and to determine the effects of depowered airbags. The National Automotive Sampling System database files from 1993 to 2000 were examined in a 3-part investigation of 22 236 individual crashes. Of the 2 103 308 occupants exposed to a full powered deployment, 3.7% sustained an eye injury compared to 1.7% of the 310 039 occupants exposed to a depowered airbag deployment. Occupants were at a significantly higher risk to sustain an airbag-induced eye injury when exposed to a full powered airbag compared with occupants exposed to a depowered airbag deployment ( P = .04). Approximately, 90% of the eye injuries in full powered airbag deployments were caused by the airbag, compared to only 35% of the depowered airbag eye injuries.