Simulation of air-bag impact on post-radial keratotomy eye using finite element analysis

Computer Modelling Study of Volume Kinetics in Intraocular Segments Following Airbag Impact Using Finite Element Analysis

Background

We have previously studied the physiological and mechanical responses of the eye to blunt trauma in various situations using finite element analysis (FEA). In this study, we evaluated the volume kinetics of an airbag impact on the eye using FEA to sequentially determine the volume change rates of intraocular segments at various airbag deployment velocities.

Methods

The human eye model we created was used in simulations with the FEA program PAM-GENERISTM (Nihon ESI, Tokyo, Japan). Different airbag deployment velocities, 30, 40, 50, 60 and 70 m/s, were applied in the forward direction. The volume of the deformed eye impacted by the airbag was calculated as the integrated value of all meshes in each segment, and the decrease rate was calculated as the ratio of the decreased volume of each segment at particular timepoints to the value before the airbag impact.

Results

The minimum volume of the anterior chamber was 63%, 69% and 50% at 50, 60 and 70 m/s airbag impact velocity, respectively, showing a curve with a sharp decline followed by gradual recovery. In contrast to the anterior chamber, the volume of the lens recovered promptly, reaching 80-90% at the end of observation, except for the case of 60 m/s. Following the decrease, the volume increased to more than that of baseline at 60 m/s. The rate of volume change of the vitreous was distributed in a narrow range, 99.2-100.4%.

Conclusion

In this study, we found a large, prolonged decrease of volume in the anterior chamber, a similar large decrease followed by prompt recovery of volume in the lens, and a time-lag in the volume decrease between these tissues. These novel findings may provide an important insight into the pathophysiological mechanism of airbag ocular injuries through this further evaluation, employing a refined FEA model representing cuboidal deformation, to develop a more safe airbag system.

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.

Simulation of Changes in Tensile Strain by Airbag Impact on Eyes After Trabeculectomy by Using Finite Element Analysis

Purpose

We studied the kinetic phenomenon of an airbag impact on eyes after trabeculectomy using finite element analysis (FEA), a computerized method for predicting how an object reacts to real-world physical effects and showing whether an object will break, to sequentially determine the responses at various airbag deployment velocities.

Methods

A human eye model was used in the simulations using the FEA program PAM-GENERISTM (Nihon ESI, Tokyo, Japan). A half-thickness incised scleral flap was created on the limbus and the strength of its adhesion to the outer sclera was set at 30%, 50%, and 100%. The airbag was set to hit the surface of the post-trabeculectomy eye at various velocities in two directions: perpendicular to the corneal center or perpendicular to the scleral flap (30° gaze-down position), at initial velocities of 20, 30, 40, 50, and 60 m/s.

Results

When the airbag impacted at 20 m/s or 30 m/s, the strain on the cornea and sclera did not reach the mechanical threshold and globe rupture was not observed. Scleral flap lacerations were observed at 40 m/s or more in any eye position, and scleral rupture extending posteriorly from the scleral flap edge and rupture of the scleral flap resulting from extension of the corneal laceration through limbal damage were observed. Even in the case of 100% scleral flap adhesion strength, scleral flap rupture occurred at 50 m/s impact velocity in the 30° gaze-down position, whereas in eyes with 30% or 50% scleral flap adhesion strength, scleral rupture was observed at an impact velocity of 40 m/s or more in both eye positions.

Conclusion

An airbag impact of ≥40 m/s might induce scleral flap rupture, indicating that current airbags may induce globe rupture in the eyes after trabeculectomy. The considerable damage caused by an airbag on the eyes of short-stature patients with glaucoma who have undergone trabeculectomy might indicate the necessity of ocular protection to avoid permanent eye damage.

Finite Element Analysis of Changes in Deformation of Intraocular Segments by Airbag Impact in Eyes of Various Axial Lengths

Background

We studied the kinetic phenomenon of an airbag impact on eyes with different axial lengths using finite element analysis (FEA) to sequentially determine the physical and mechanical responses of intraocular segments at various airbag deployment velocities.

Methods

The human eye model we created was used in simulations with the FEA program PAM-GENERISTM. The airbag was set to impact eyes with axial lengths of 21.85 mm (hyperopia), 23.85 mm (emmetropia) and 25.85 mm (myopia), at initial velocities of 20, 30, 40, 50 and 60 m/s. The deformation rate was calculated as the ratio of the length of three segments, anterior chamber, lens and vitreous, to that at the baseline from 0.2 ms to 2.0 ms after the airbag impact.

Results

Deformation rate of the anterior chamber was greater than that of other segments, especially in the early phase, 0.2-0.4 ms after the impact (P < 0.001), and it reached its peak, 80%, at 0.8 ms. A higher deformation rate in the anterior chamber was found in hyperopia compared with other axial length eyes in the first half period, 0.2-0.8 ms, followed by the rate in emmetropia (P < 0.001). The lens deformation rate was low, its peak ranging from 40% to 75%, and exceeded that of the anterior chamber at 1.4 ms and 1.6 ms after the impact (P < 0.01). The vitreous deformation rate was lower throughout the simulation period than that of the other segments and ranged from a negative value (elongation) in the later phase.

Conclusion

Airbag impact on the eyeball causes evident deformation, especially in the anterior chamber. The results obtained in this study, such as the time lag of the peak deformation between the anterior chamber and lens, suggest a clue to the pathophysiological mechanism of airbag ocular injury.

Bilateral Angle Recession and Chronic Post-Traumatic Glaucoma: A Review of the Literature and a Case Report

Ocular trauma affects millions of people worldwide and is a leading cause of secondary glaucoma. Angle recession is the main cause of post-traumatic glaucoma after blunt eye trauma, and it is usually unilateral. The aim of this paper is to investigate the possible causes of angle recession with a bilateral presentation. Airbag activation during traffic accidents is a likely cause to be ruled out, along with repeated head or eye trauma, due to contact sports or a history of physical abuse. These aspects can aid in early detection, appropriate management, and improved outcomes for patients with ocular trauma. Finally, we report the case of a 75-year-old Caucasian man who developed a bilateral angle recession after an airbag impact, with advanced glaucoma in the right eye and ocular hypertension in the left eye. To our knowledge, this is the first case in the literature of chronic post-traumatic glaucoma probably caused by an airbag.

Biomechanics of open-globe injury: a review

Open-globe injury is a common cause of blindness clinically caused by blunt trauma, sharp injury, or shock waves, characterised by rupture of the cornea or sclera and exposure of eye contents to the environment. It causes catastrophic damage to the globe, resulting in severe visual impairment and psychological trauma to the patient. Depending on the structure of the globe, the biomechanics causing ocular rupture can vary, and trauma to different parts of the globe can cause varying degrees of eye injury. The weak parts or parts of the eyeball in contact with foreign bodies rupture when biomechanics, such as external force, unit area impact energy, corneoscleral stress, and intraocular pressure exceed a certain value. Studying the biomechanics of open-globe injury and its influencing factors can provide a reference for eye-contact operations and the design of eye-protection devices. This review summarises the biomechanics of open-globe injury and the relevant factors.

Finite element analysis of changes in tensile strain and deformation by airbag impact in eyes of various axial lengths

Purpose

Airbags have substantially reduced mortality and morbidity, while ocular injuries caused by airbags have been reported. We applied a three-dimensional finite element analysis (FEA) model we have established for evaluation of the deformation of an intact eyeball of various axial lengths induced by an airbag impact at various impact velocities.

Methods

A model human eye we have created was used in simulations with an FEA program, PAM-GENERIS™ (Nihon ESI, Tokyo, Japan). The airbag was set to impact eyes with various axial lengths of 21.85 mm (hyperopia), 23.85 mm (emmetropia) and 25.85 mm (myopia), at initial velocities of 30, 40, 50 and 60 m/s. Changes in the shape of the eye and the strain induced were calculated. Deformation of the eye in a cross-sectional view was displayed sequentially in slow motion.

Results

We found that considerable damage, such as corneal or scleral lacerations, was observed especially at higher impact velocities, such as 50 or 60 m/s, in eyes with any axial length. Deformation was most evident in the anterior segment. The decrease rate of axial length was greatest in the hyperopic eye, followed by the myopic eye, and the emmetropic eye.

Conclusions

It was shown that hyperopic eyes are most susceptible to deformation by an airbag impact in this simulation. The considerable deformation by an airbag impact on the eye during a traffic accident shown in this study might indicate the necessity of ocular protection to avoid permanent eye damage.

Finite Element Analysis of Changes in Tensile Strain by Airsoft Gun Impact on Eye and Deformation Rate in Eyes of Various Axial Lengths

Purpose

We have carried out three-dimensional finite element analysis (FEA) to determine the physical and mechanical response in several ocular injuries. We applied this FEA model to evaluate an airsoft gun impact on an eye and the deformation rate of eyes of various axial lengths at various velocities.

Methods

This study was carried out on a human eye model using an FEA program created by Nihon, ESI Group. The airsoft gun pellet was set to impact the eye at initial velocities of 45, 60 and 75 m/s with the addition of variation in axial length of 20 mm (hyperopia), 22 mm (emmetropia), 24 mm (myopia) and 26 mm (high myopia). Deformation of the eye was calculated as the decrease rate of the volume of the eyeball and the decrease rate of the axial length.

Results

In all emmetropic cases, the cornea reached its strain threshold during the impact, and scleral strain showed a patchy strength distribution in the simulation. The deformation was most evident in the anterior segment, while deformation of the posterior segment was less. The decrease rate of the volume of the eyeball and decrease rate of the axial length were highest in the hyperopic eye, followed by the emmetropic eye and myopic eye, and the high myopic eye showed the lowest decrease rates among the four axial lengths in all impact velocity simulations.

Conclusion

These results suggest that hyperopic eyes are most susceptible to deformation by an airsoft gun impact compared with other axial length eye models in this simulation. The considerable deformation by an airsoft gun impact shown in this study might indicate the necessity of ocular protection to avoid permanent eye injury. FEA using a human eyeball model might be a useful method to analyze and predict the mechanical features of ocular injury by an airsoft gun.

Finite Element Analysis of Air Gun Impact on Post-Keratoplasty Eye

Purpose

Due to the mechanical vulnerability of eyes that have undergone penetrating keratoplasty (PKP), it is clinically important to evaluate the possibility of corneal wound dehiscence by blunt impact. We have previously developed a simulation model resembling a human eye based on information obtained from cadaver eyes and applied three-dimensional finite element analysis (FEA) to determine the physical and mechanical response to an air gun impact at various velocities on the post-PKP eye.

Methods

Simulations in a human eye model were performed with a computer using a FEA program created by Nihon, ESI Group. The air gun pellet was set to impact the eye at three-different velocities in straight or 12° up-gaze positions with the addition of variation in keratoplasty suture strength of 30%, 50% and 100% of normal corneal strength.

Results

Furthermore to little damage in the case of 100% strength, in cases of lower strength in a straight-gaze position, wound rupture seemed to occur in the early phase (0.04-0.06 ms) of impact at low velocities, while regional break was observed at 0.14 ms after an impact at high velocity (75 m/s). In contrast, wound damage was observed in the lower quadrant of the suture zone and sclera in 12° up-gaze cases. Wound damage was observed 0.08 ms after an impact threatening corneoscleral laceration, and the involved area being larger in middle impact velocity (60 m/s) simulations than in lower impact velocity simulations, and larger damaged area was observed in high impact velocity cases and leading to corneoscleral laceration.

Conclusion

These results suggest that the eye is most susceptible to corneal damage around the suture area especially with a straight-gaze impact by an air gun, and that special precautionary measures should be considered in patients who undergo PKP. FEA using a human eyeball model might be a useful method to analyze and predict the mechanical features of eyes that undergo keratoplasty.

Biomechanical simulation of eye-airbag impacts during vehicle accidents

Airbags are safety devices in vehicles effectively suppressing passengers' injuries during accidents. Although there are still many cases of eye injuries reported due to eye-airbag impacts in recent years. Biomechanical approaches are now feasible and can considerably help experts to investigate the issue without ethical concerns. The eye-airbag impact-induced stresses/strains in various components of the eye were found to investigate the risk of injury in different conditions (impact velocity and airbag pressure). Three-dimensional geometry of the eyeball, fat and bony socket as well as the airbag were developed and meshed to develop a finite element model. Nonlinear material properties of the vitreous body and sclera were found through the in vitro tests on ovine samples and for the other components were taken from the literature. The eye collided the airbag due to the velocity field in the dynamic explicit step in Abaqus. Results of compression tests showed a nonlinear curve for vitreous body with average ultimate stress of 22 (18-25) kPa. Tensile behavior of sclera was viscoelastic nonlinear with ultimate stresses changing from 2.51 (2.3-2.7) to 4.3 (4-4.6) MPa when loading strain rate increased from 10 to 600 mm/min. Sclera, ciliary body, cornea and lens were the eye components with highest stresses (maximum stress reached up to 9.3 MPa). Cornea, retina and choroid experienced the highest strains with the maximum up to 14.1%. According to the previously reported injury criteria for cornea, it was at high risk of injury considering both stress and strains. Reduced pressure of the airbag was beneficial decreased stress of all components. Comprehensive investigations in this area can disclose biomechanical behavior of the eye during eye-airbag impact. Effective guidelines can be drawn for airbag design for instance the airbag pressure which reduces risk of eye injury.

Simulation of airbag impact on eyes with different axial lengths after transsclerally fixated posterior chamber intraocular lens by using finite element analysis

Purpose

To determine the biomechanical response of an impacting airbag on eyes with different axial lengths with transsclerally fixated posterior chamber intraocular lens (PC IOL).

Materials and methods

Simulations in a model human eye were performed with a computer using a finite element analysis program created by Nihon, ESI Group. The airbag was set to be deployed at five different velocities and to impact on eyes with three different axial lengths. These eyes were set to have transsclerally fixated PC IOL by a 10-0 polypropylene possessing a tensile force limit of 0.16 N according to the United States Pharmacopeia XXII.

Results

The corneoscleral opening was observed at a speed of 40 m/second or more in all model eyes. Eyes with the longest axial length of 25.85 mm had the greatest extent of deformity at any given impact velocity. The impact force exceeded the tensile force of 10-0 polypropylene at an impact velocity of 60 m/second in all eyes, causing breakage of the suture.

Conclusion

Eyes with transsclerally fixated PC IOL could rupture from airbag impact at high velocities. Eyes with long axial lengths experienced a greater deformity upon airbag impact due to a thinner eye wall. Further basic research on the biomechanical response for assessing eye injuries could help in developing a better airbag and in the further understanding of ocular traumas.

Shear behavior of bovine scleral tissue

Ocular tissue properties have been widely studied in tension and compression for humans and a variety of animals. However, direct shear testing of the tissues of the sclera appear to be absent from the literature even though modeling, analyses, and anatomical studies have indicated that shear may play a role in the etiology of primary open angle glaucoma (POAG). In this work, the mechanical behavior of bovine scleral tissue in shear has been studied in both out-of-plane and in-plane modes of deformation. Stress-strain and relaxation tests were conducted on tissue specimens at controlled temperature and hydration focusing on trends related to specimen location and orientation. There was generally found to be no significant effect of specimen orientation and angular location in the globe on shear stiffness in both modes. The in-plane response, which is the primary load carrying mode, was found to be substantially stiffer than the out-of-plane mode. Also, within the in-plane studies, tissue further from the optic nerve was stiffer than the near tissue. The viscosity coefficient of the tissue varied insignificantly with distance from the optic nerve, but overall was much higher in-plane than out-of-plane.

EMBEDDED COLLAGEN DEFORMATION MODELS FOR COMPUTATIONAL MODELING OF HEALTHY, KERATOCONIC, AND CROSSLINKED CORNEAS

Collagen plays an extremely important role in carrying forces and maintaining the shape of the cornea. In keratoconus, the cornea shape can become distorted to the extent that normal vision is impossible, and the amount crosslinking between collagen fibrils are generally lower than in healthy eyes. In contrast, riboflavin-induced crosslinks can strengthen and stiffen the cornea. This article examined quantitatively how the extent of crosslinking in collagen fibrils influences the overall mechanical behavior of corneal tissue. Three models for the stress–strain behavior of the fibrils were examined, which is a function of the crosslink density within the fibrils. These models were then embedded in a matrix model, and tensile tests of cornea strips were examined using a finite element program. Results were compared with experiments from the literature for both normal and crosslinked corneas.

Constitutive behavior of ocular tissues over a range of strain rates

The constitutive behavior of bovine scleral and corneal tissues is measured in tension and compression, at quasi-static and moderate strain rates. Experiments are conducted at strain rates up to about 50 strain per second by a pneumatic testing system developed to overcome noise and measurement difficulties associated with the time dependent test of low impedance materials. Results for the tissues at room and the natural bovine body temperatures are similar and indicate that ocular tissue exhibits nonlinear stiffening for increasing strain rates, a phenomena termed rate hardening. For example, at a tensile strain rate of 29/s, corneal tissue is found to develop 10 times the stress that it does quasi-statically at the same strain. Thus, conventional constitutive models will grossly underpredict stresses occurring in the corneo-scleral shell due to moderate dynamic events. This has implication to the accuracy of ocular injury models, the study of the stress field in the corneo-scleral shell for glaucoma research and tonometry measurements. The measured data at various strain rates is represented using the general framework of a constitutive model that has been used to represent biological tissue mechanical data. Here it is extended to represent the measured data of the ocular tissues over the range of tested strain rates. Its form allows for straightforward incorporation in various numerical codes. The experimental and analytical methods developed here are felt to be applicable to the test of human ocular tissue.

Evaluation of Different Projectiles in Matched Experimental Eye Impact Simulations

Eye trauma results in 30,000 cases of blindness each year in the United States and is the second leading cause of monocular visual impairment. Eye injury is caused by a wide variety of projectile impacts and loading scenarios with common sources of trauma being motor vehicle crashes, military operations, and sporting impacts. For the current study, 79 experimental eye impact tests in literature were computationally modeled to analyze global and localized responses of the eye to a variety of blunt projectile impacts. Simulations were run with eight different projectiles (airsoft pellets, baseball, air gun pellets commonly known as BBs, blunt impactor, paintball, aluminum, foam, and plastic rods) to characterize effects of the projectile size, mass, geometry, material properties, and velocity on eye response. This study presents a matched comparison of experimental test results and computational model outputs including stress, energy, and pressure used to evaluate risk of eye injury. In general, the computational results agreed with the experimental results. A receiver operating characteristic curve analysis was used to establish the stress and pressure thresholds that best discriminated for globe rupture in the matched experimental tests. Globe rupture is predicted by the computational simulations when the corneoscleral stress exceeds 17.21 MPa or the vitreous pressure exceeds 1.01 MPa. Peak stresses were located at the apex of the cornea, the limbus, or the equator depending on the type of projectile impacting the eye. A multivariate correlation analysis revealed that area-normalized kinetic energy was the best single predictor of peak stress and pressure. Additional incorporation of a relative size parameter that relates the projectile area to the area of the eye reduced stress response variability and may be of importance in eye injury prediction. The modeling efforts shed light on the injury response of the eye when subjected to a variety of blunt projectile impacts and further validate the eye model’s ability to predict globe rupture. Results of this study are relevant to the design and regulation of safety systems and equipment to protect against eye injury.

Eye trauma in boxing

In boxing, along with a few other sports, trauma is inherent to the nature of the sport; therefore it is considered a high-risk sport for ocular injuries. The long-term morbidity of ocular injuries suffered by boxers is difficult to estimate due to the lack of structured long-term follow-up of these athletes. Complications of blunt ocular trauma may develop years after the athlete has retired from the ring and is no longer considered to be at risk for boxing-related injuries. This article describes the wide range of eye injuries a boxer can sustain, and their immediate and long-term clinical management.

Computer modelling study of the mechanism of optic nerve injury in blunt trauma

AIM

The potential causes of the optic nerve injury as a result of blunt object trauma, were investigated using a computer model.

METHODS

A finite element model of the eye, the optic nerve, and the orbit with its content was constructed to simulate blunt object trauma. We used a model of the first phalanx of the index finger to represent the blunt body. The trauma was simulated by impacting the blunt body at the surface between the globe and the orbital wall at velocities between 2-5 m/s, and allowing it to penetrate 4-10 mm below the orbital rim.

RESULTS

The impact caused rotations of the globe of up to 5000 degrees /s, lateral velocities of up to 1 m/s, and intraocular pressures (IOP) of over 300 mm Hg. The main stress concentration was observed at the insertion of the nerve into the sclera, at the side opposite to the impact.

CONCLUSIONS

The results suggest that the most likely mechanisms of injury are rapid rotation and lateral translation of the globe, as well as a dramatic rise in the IOP. The strains calculated in the study should be sufficiently high to cause axonal damage and even the avulsion of the nerve. Finite element computer modelling has therefore provided important insights into a clinical scenario that cannot be replicated in human or animal experiments.

Modelling of orbital deformation using finite-element analysis

The purpose of this study was to develop a three-dimensional finite-element model (FEM) of the human orbit, containing the globe, to predict orbital deformation in subjects following a blunt injury. This study investigated the hypothesis that such deformation could be modelled using finite-element techniques. One patient who had CT-scan examination to the maxillofacial skeleton including the orbits, as part of her treatment, was selected for this study. A FEM of one of the orbits containing the globe was constructed, based on CT-scan images. Simulations were performed with a computer using the finite-element software NISA (EMRC, Troy, USA). The orbit was subjected to a blunt injury of a 0.5 kg missile with 30 ms(-1) velocity. The FEM was then used to predict principal and shear stresses or strains at each node position. Two types of orbital deformation were predicted during different impact simulations: (i) horizontal distortion and (ii) rotational distortion. Stress values ranged from 213.4 to 363.3 MPa for the maximum principal stress, from -327.8 to -653.1 MPa for the minimum principal stress, and from 212.3 to 444.3 MPa for the maximum shear stress. This is the first finite-element study, which demonstrates different and concurrent patterns of orbital deformation in a subject following a blunt injury. Finite element modelling is a powerful and invaluable tool to study the multifaceted phenomenon of orbital deformation.

Orbital Stress Analysis—Part I: Simulation of Orbital Deformation Following Blunt Injury by Finite Element Analysis Method

PURPOSE

The purpose of this study was to develop a 3-dimensional finite element model (FEM) of the human orbit, housing the globe, to predict orbital deformation in subjects following a blunt injury.

MATERIALS AND METHODS

A FEM of the human orbit including the eye, fatty tissues, and extraocular muscles was constructed. Simulations were performed with a computer using the finite element software NISA (EMRC, Troy, MI). The orbit was subjected to a blunt injury of a 0.5 kg missile with 30 m/s velocity. The FEM was then used to predict principal and shear stresses/strains at each node position.

RESULTS

Two types of orbital deformation were predicted during different impact simulations: a) horizontal distortion and b) rotational distortion. Stress values ranged from 112.12 to 262.3 MPa for the maximum principal stress, from -226.8 to -552.1 MPa for the minimum principal stress, and from 111.3 to 343.3 MPa for the maximum shear stress.

CONCLUSION

This is the first finite element study that demonstrates different and concurrent patterns of orbital deformation in subjects following a blunt injury. FEM is a powerful and invaluable tool to study the multifaceted phenomenon of orbital deformation.

Simulation of air-bag impact on an eye with transsclerally fixated posterior chamber intraocular lens using finite element analysis

PURPOSE

To determine the physical and mechanical conditions of an impacting air bag that would rupture an eye with a transsclerally fixated posterior chamber intraocular lens (IOL).

SETTING

Numerical simulation study on a computer.

METHODS

Simulations in a model human eye were performed with a computer using the finite element analysis program PAM-CRASH (Nihon ESI). The air bag was set to impact the surface of an eye with a transsclerally fixated posterior chamber IOL at various velocities. The tensile force limit of a 10-1 polypropylene suture was assumed to be 0.16 N, which is specified in the U.S. Pharmacopeia XXII.

RESULTS

At the lowest velocity of 20.0 m/s, 10-0 polypropylene sutures were not likely to break. Sutures fixating the IOL might break and a corneoscleral incision was likely to open after 0.3 second at the medium impacting velocity (30 m/s). Suture rupture was very likely at the highest velocity (40 m/s) since the tensile force on the sutures continuously exceeded the breaking force after the impact.

CONCLUSIONS

In an eye with a transsclerally fixated posterior chamber IOL, severe ocular trauma can be caused by an air bag at high velocity. Small individuals such as elderly women are at greater risk for air-bag ocular injury. Further research on modifying air-bag design and deployment is important to minimize the risk for ocular injury.

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

Over 2.4 million eye injuries occur each year in the US, with over 30,000 patients left blind as a result of the trauma. The majority of these injuries occur in automobile crashes, military operations and sporting activities. This paper presents a nonlinear finite element model of the eye and the results of 22 experiments using human eyes to validate for globe rupture injury prediction. The model of the human eye consists of the cornea, sclera, lens, ciliary body, zonules, aqueous humor and vitreous body. Lagrangian membrane elements are used for the cornea and sclera, Lagrangian bricks for the lens, ciliary, and zonules, and Eulerian brick elements comprise the aqueous and vitreous. Nonlinear, isotropic material properties of the sclera and cornea were gathered from uniaxial tensile strip tests performed up to rupture. Dynamic modeling was performed using LS-Dyna. Experimental validation tests consisted of 22 tests using three scenarios: impacts from foam particles, BB's, and baseballs onto fresh eyes used within 24 hours postmortem. The energies of the projectiles were chosen so as to provide both globe rupture and no rupture tests. Displacements of the eye were recorded using high speed color video at 7100 frames per second. The matched simulations predicted rupture of the eye when rupture was seen in the BB and baseball tests, and closely predicted displacements of the eye for the foam tests. Globe rupture has previously been shown to occur at peak stresses of 9.4 MPa using the material properties included in the model. Because of dynamic effects and improvements in boundary conditions resulting from a more realistic modeling of the fluid in the anterior and posterior chambers, the stresses can be much higher than those previously predicted, with the globe remaining intact. The model is empirically verified to predict globe rupture for stresses in the corneoscleral shell exceeding 23 MPa, and local dynamic pressures exceeding 2.1 MPa. The model can be used as a predictive aid to reduce the burden of eye injury, and can serve as a validated model to predict globe rupture.