Traumatic blindness after airbag deployment: bilateral lenticular dislocation

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.

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.

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.

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.

Bilateral posterior dislocation of the crystalline lens after a head injury sustained during a seizure

This article presents a case of bilateral posterior dislocations of the crystalline lens in a patient with epilepsy who presented with reduced vision and anisocoria 2 weeks after having sustained head injuries during a seizure. The possibility of lens dislocation was raised only at this time, and subsequently confirmed on computed tomography. Such patients may require prompt referral to the ophthalmologist to treat complications such as functional aphakia, uveitis and more seriously pupillary block glaucoma. This case highlights the importance of ocular examination of head injuries to rule out possible ophthalmological pathology.

The Effects of Depowered Airbags on Skin Injuries in Frontal Automobile Crashes

The purpose of this study was to determine the effects of depowered frontal airbags on the incidence of skin injuries. The National Automotive Sampling System database files from 1993 to 2000 were examined in a study including 2,246,524 occupants exposed to airbag deployment in the United States. There was no significant difference between full-powered and depowered airbags, with 60.2 percent of those exposed to a full-powered deployment sustaining a skin injury versus 59.5 percent of occupants exposed to a depowered airbag (p = 0.19). Whether occupants were exposed to a full-powered airbag (1,936,485 occupants) or a depowered airbay (310,039 occupants), the majority of skin injuries were to the upper extremity and the face. Regardless of airbag power, the overwhelming majority of the skin injuries were minor (99.8 percent). There was not a significantly greater risk of injury from any source for occupants exposed to a depowered airbag or a full-powered airbag (p = 0.87). The data suggest that the implementation of depowered airbags did not affect the number, seriousness, location, or source of skin injuries.

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.

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.

Airbags and eye injuries: epidemiology, spectrum of injury, and analysis of risk factors

Although airbags measurably reduce the overall risk of injury to adults (including eye injury), and death from motor vehicle accidents, injuries attributed to airbag deployment have been reported. To identify reported cases of ocular trauma related to airbag deployment, a MEDLINE search from 1991 to 2000 was performed. A total of 263 injuries in 101 patients were identified. Patient demographics, details of the accident, specific ocular structures injured, and visual outcomes when available where tabulated and analyzed. The most common of these affect the eyes. Damage to the orbit and virtually every ocular and adnexal structure has been seen. Although most injuries are self-limited and do not significantly compromise vision, some result in severe, permanent visual loss. Most common is damage to anterior structures due to either blunt, contusive forces and/or chemical injury. Posterior segment trauma is less common but generally more visually devastating because of the involvement of the retina or optic nerve. Data are not available to determine whether the wearing of eyeglasses or previous intraocular surgery affects the nature, severity, or outcome of these injuries. Awareness of the spectrum of airbag-associated ocular trauma will help physicians recognize these problems early and optimize their management. Data derived from analyses of these injuries will be critical to the development of safer, more effective devices.

Partial Dislocation of Laser in situ Keratomileusis Flap by Air Bag Injury

PURPOSE

A patient developed significant corneal complications from air bag deployment, 17 months after laser in situ keratomileusis (LASIK).

METHODS

Case report, slit-lamp microscopy, and review of the medical literature.

RESULTS

A 37-year-old woman underwent bilateral LASIK with resultant 20/20 uncorrected visual acuity. Seventeen months later, she sustained facial and ocular injuries from air bag deployment during a motor vehicle accident. Examination revealed bilateral corneal abrasions, partial dislocation of the right corneal LASIK flap, and a hyphema in the right eye. The LASIK flap was realigned, but recovery was complicated by a slowly healing epithelial defect and flap edema. One month following the injury, epithelial ingrowth beneath the LASIK flap was noted. Surgical elevation of the flap and removal of the epithelial ingrowth was performed. Eight months later, epithelial ingrowth was absent and the visual acuity was 20/40. Residual irregular astigmatism necessitated rigid gas permeable contact lens fitting to achieve 20/20 visual acuity.

CONCLUSIONS

Air bags may cause significant ocular trauma. The wound healing response of LASIK allows corneal flap separation from its stromal bed for an indeterminate time after surgery. Discussion of the possible risk of corneal trauma as part of informed consent prior to LASIK may be appropriate.

Atlanto-occipital dislocation: an unusual lethal airbag injury

Airbag-induced injury fatality is increasing in frequency. We present the case of a 6-year-old passenger who sustained a fatal atlanto-occipital dislocation associated with airbag deployment in a low-speed motor vehicle crash. The current literature regarding airbag fatalities and methods to ameliorate airbag-induced injury are reviewed.

Traumatic anterior lens dislocation: a case report

A 45-year-old man presented to the emergency department complaining of decreased vision and pain in the left eye after blunt trauma to the eye. On evaluation, the vision was limited to detecting hand motions, and the intraocular pressure was 37 mmHg. Secondary acute angle-closure glaucoma, with pupillary block due to anterior dislocation of the lens, was diagnosed. The intraocular pressure remained elevated after medical therapy, and the patient underwent intracapsular cataract extraction and anterior vitrectomy. The possibility of elevated intraocular pressure due to lens dislocation or other types of secondary glaucoma should be considered after blunt ocular trauma.

On burn injuries related to airbag deployment

Airbags have been shown as a vital, supplemental restraining device that save lives and reduce morbidity associated with motor vehicles crashes. However, as with any developing technology, airbags have also been identified in some instances, as the source of injuries which, have been well described in the literature. To a significantly lesser degree, burns due to airbag deployment (about 7-8% of these injuries) have been reported. These injuries will be seen more frequently as more vehicles are equipped with airbags and should be suspected in drivers and passengers involved in accidents in which airbags have been activated. This article, reviews the various types of burns and their pathogenesis, found in crashes involving airbag deployments.

Air bags: an update

Overwhelming evidence shows that air bags save lives and reduce morbidity associated with MVCs. The resulting benefits far outweigh the risks of air bag injury or death. Emergency nurses play a pivotal role in educating the public about active seat belt use in conjunction with passive restraint systems such as air bags. Air bags cannot be viewed as a single solution or panacea to occupant protection. Air bags are designed as supplemental devices to be used with seat belts and require the active participation of the user for maximum benefit and safety.