Mechanism of traumatic retinal detachment in blunt impact: A finite element study

Ocular injuries among patients with major trauma in England and Wales from 2004 to 2021

BACKGROUND

Ocular trauma is a significant cause of blindness and is often missed in polytrauma. No contemporary studies report eye injuries in the setting of severe trauma in the UK. We investigated ocular injury epidemiology and trends among patients suffering major trauma in England and Wales from 2004 to 2021.

METHODS

We conducted a retrospective study utilising the Trauma Audit and Research Network (TARN) registry. Major trauma cases with concomitant eye injuries were included. Major trauma was defined as Injury Severity Score >15. Ocular injuries included globe, cranial nerve II, III, IV, and VI, and tear duct injuries. Orbital fractures and adnexal and lid injuries were not included. Demographics, injury profiles, and outcomes were extracted. We report descriptive statistics and 3-yearly trends.

RESULTS

Of 287 267 major trauma cases, 2368 (0.82%) had ocular injuries: prevalence decreased from 1.87% to 0.66% over the 2004-2021 period (P < 0.0001). Males comprised 72.2% of ocular injury cases, median age was 34.5 years. The proportion of ocular injuries from road traffic collisions fell from 43.1% to 25.3% while fall-related injuries increased and predominated (37.6% in 2019/21). Concomitant head injury occurred in 86.6%. The most common site of ocular injury was the conjunctiva (29.3%). Compared to previous TARN data (1989-2004), retinal injuries were threefold more prevalent (5.9% vs 18.5%), while corneal injuries were less (31.0% vs 6.6%).

CONCLUSIONS

Whilst identifying eye injuries in major trauma is challenging, it appears ocular injury epidemiology in this setting has shifted, though overall prevalence is low. These findings may inform prevention strategies, guideline development and resource allocation.

Posterior Retinal Breaks Secondary to Closed-Globe Blunt Ocular Trauma

Purpose: To describe 2 cases of posterior pole retinal tears resulting from closed-globe trauma. Methods: Two cases of retinal breaks in the posterior pole after blunt ocular trauma were evaluated, and the relevant literature was reviewed. Results: Two eyes of 2 patients with posterior pole retinal tears secondary to closed-globe trauma were included. One patient had a pars plana vitrectomy with laser retinopexy and gas tamponade; the final Snellen visual acuity (VA) was 20/200. The second patient was treated with indirect laser retinopexy; the final Snellen VA was counting fingers. Conclusions: The rapid deformation of the globe in response to blunt ocular trauma may create significant tangential stress on the retina, leading to stretch breaks in the posterior pole. Clinicians should follow patients with a closed-globe injury to watch for retinal breaks in the posterior pole, in particular when a hemorrhage or other pathology obscures the view.

Modeling of inflicted head injury by shaking trauma in children: what can we learn? : Update to parts I&II: A systematic review of animal, mathematical and physical models

Inflicted shaking trauma can cause injury in infants, but exact injury mechanisms remain unclear. Controversy exists, particularly in courts, whether additional causes such as impact are required to produce injuries found in cases of (suspected) shaking. Publication rates of studies on animal and biomechanical models of inflicted head injury by shaking trauma (IHI-ST) in infants continue rising. Dissention on the topic, combined with its legal relevance, makes maintaining an up-to-date, clear and accessible overview of the current knowledge-base on IHI-ST essential. The current work reviews recent (2017-2023) studies using models of IHI-ST, serving as an update to two previously published reviews. A systematic review was conducted in Scopus and PubMed for articles using animal, physical and mathematical models for IHI-ST. Using the PRISMA methodology, two researchers independently screened the publications. Two, five, and ten publications were included on animal, physical, and mathematical models of IHI-ST, respectively. Both animal model studies used rodents. It is unknown to what degree these can accurately represent IHI-ST. Physical models were used mostly to investigate gross head-kinematics during shaking. Most mathematical models were used to study local effects on the eye and the head's internal structures. All injury thresholds and material properties used were based on scaled adult or animal data. Shaking motions used as inputs for animal, physical and mathematical models were mostly greatly simplified. Future research should focus on using more accurate shaking inputs for models, and on developing or and validating accurate injury thresholds applicable for shaking.

Numerical simulation of mechanical properties of epiretinal membrane peeling

An epiretinal membrane (ERM) is a fibrocellular proliferation on the inner surface of the retina causing blurred and distorted central vision. Surgery is the only effective method for ERM removal. This paper investigated the mechanical properties of ERM peeling using the finite element (FE) method. A FE model of ERM formation on the retina surface was constructed. The failure criterion was applied to the attachment pegs to represent the adhesive force between the ERM and retina. The simulation results were consistent with the experimental data in published research. The maximum peeling force was 4.1 mN at a peeling velocity of 2 mm/s and an angle of 30°. The peeling force was minimum at the peeling angle of 45° and increased with the increase in peeling velocity and Young's modulus of the membrane. The outcome of this paper can improve the safety and efficiency of ERM removal.

Assessment of age-related change of the ocular support system

To estimate the material stiffness of the orbital soft tissue in human orbits using an inverse numerical analysis approach, which could be used in future studies to understand the behaviour under dynamic, non-contact tonometry or simulate various ophthalmological conditions. Clinical data were obtained for the left eye of 185 Chinese participants subjected to a complete ophthalmic examination, including tests by the Corvis ST and Pentacam. 185 numerical models of the eye globes were built with idealised geometry of the sclera while considering the corneal tomography measured by the Pentacam. The models were extended to include representations of the orbital soft tissue (OST), which were given idealised geometry. The movement of the whole eye in response to an air-puff directed at the central cornea was examined and used in an inverse analysis process to estimate the biomechanical stiffness parameters of the OST. The results indicated a weak correlation of E _t with the progression of age, regardless of the stress at which E _t was calculated. However, there was evidence of significant differences in E _t between some of the age groups. There was statistical evidence of significant differences between E _t in the age range 20< years < 43 relative to E _t in OST with age ranges 43< years < 63 (p = 0.022) and 63< years < 91 (p = 0.011). In contrast, E _t in OST with age ranges 43< years < 63 and 63< years < 91 were not significantly different (p = 0.863). The optimised mechanical properties of the OST were found to be almost four times stiffer than properties of fatty tissue of previous experimental work. This study consolidated previous findings of the role of extraocular muscles on the ocular suppor system. In addition, the rotation of the globe during corvis loading is suggested to be of posterior components of the globe and shall be further investigated.

Experimental evidence to understand mechanical causes of retinal detachment following blunt trauma

PURPOSE

This study aimed to perform an in vitro experiment to simulate retinal detachment caused by blunt impact, and provide experimental evidence to understand mechanical causes of traumatic retinal detachment.

METHODS

The experiment was conducted on twenty-two fresh porcine eyes using a bespoke pendulum testing device at two energy levels (0.1J for low energy and 1.0J for high energy). We examined dynamic forces and mechanical responses to the impact, including global deformations, intraocular pressure changes and the energy absorption. Another set of twenty-two eyes underwent pathological examination immediately after being subjected to blunt impact. Twelve additional intact eyes were examined as controls. All pathological sections were scored to indicate whether retinal detachment had occurred.

RESULTS

A dynamic variation in intraocular pressure was detected following impact and exhibited an approximate sinusoidal oscillation-attenuation profile. The peaks of impact force were 12.9 ± 1.9 N at low-energy level and 34.8 ± 9.8 N at high-energy level, showing a significant difference (p < 0.001). The positive and negative peaks of intraocular pressure were 149.4 ± 18.9 kPa and -10.9 ± 7.2 kPa at low-energy level, and 274.5 ± 55.2 kPa and -35.7 ± 23.7 kPa at high-energy level, showing significant differences (p < 0.001 for both levels). Retinal detachments were observed in damaged eyes while few detachments were found in control eyes. The occurrence rate of retinal detachment differed significantly (p < 0.05) between the high- and low-energy impact groups.

CONCLUSIONS

This study provided experimental evidence that shockwaves produced by blunt trauma break the force equilibrium and lead to the oscillation and negative pressure, which mainly contribute to traumatic retinal detachment.

The adhesion behavior of the retina

Ocular diseases and treatment related to rhegmatogenous retinal detachment (RRD) are highly correlated with retinal adhesion behavior. Therefore, this paper proposes to study the adhesion behavior of the intact retina. This can provide theoretical guidance for the treatment and research of retinal detachment (RD) related diseases. To systematically analyze this aspect, two experiments were performed on the porcine retina. The pull-off test combined with the modified JKR theory was used to study the adhesion behavior of the vitreoretinal interface, while the peeling test was used to study the adhesion behavior of the chorioretinal interface. In addition, the adhesion phase involved in the pull-off test was simulated and analyzed by building the corresponding finite element method (FEM). The experimental results of adhesion force on the vitreoretinal interface were obtained by pull-off test with five sizes of rigid punch. The experimental value of the pull-off force F_PO tends to increase gradually with increasing punch radius in the range of 0.5-4 mm. A comparison of the experimental results with the simulation results shows that they are in a well agreement. And there is no statistical difference between the experimental and theoretical values of the pull-off force F_PO. In addition, the values of retinal adhesion work were also obtained by pull-off test. Interestingly, there is a significant scale effect of the retinal work of adhesion. Finally, the peeling test gave a maximum peeling strength T_Max of about 13 mN/mm and a stable peeling strength T_D of about 11 mN/mm between the retina and the choroid. The pull-off test well shows the process of retinal traction by the diseased vitreous at the beginning of RRD. A comparison of the experimental results with the finite element results verifies the accuracy of the simulation. The peeling test well investigated the adhesion behavior between the retina and the choroid and obtained key biomechanical data (peeling strength, etc.). The combination of the two experiments allows a more systematic study of the whole retina. This research can provide more complete material parameters for finite element modeling of retina-related diseases, and it also can provide the theoretical guidance for individualized design of retinal repair surgery.

An Inverse Method to Determine Mechanical Parameters of Porcine Vitreous Bodies Based on the Indentation Test

The vitreous body keeps the lens and retina in place and protects these tissues from physical insults. Existing studies have reported that the mechanical properties of vitreous body varied after liquefaction, suggesting mechanical properties could be effective parameters to identify vitreous liquefaction process. Thus, in this work, we aimed to propose a method to determine the mechanical properties of vitreous bodies. Fresh porcine eyes were divided into three groups, including the untreated group, the 24 h liquefaction group and the 48 h liquefaction group, which was injected collagenase and then kept for 24 h or 48 h. The indentation tests were carried out on the vitreous body in its natural location while the posterior segment of the eye was fixed in the container. A finite element model of a specimen undertaking indentation was constructed to simulate the indentation test with surface tension of vitreous body considered. Using the inverse method, the mechanical parameters of the vitreous body and the surface tension coefficient were determined. For the same parameter, values were highest in the untreated group, followed by the 24 h liquefaction group and the lowest in the 48 h liquefaction group. For C₁₀ in the neo-Hookean model, the significant differences were found between the untreated group and liquefaction groups. This work quantified vitreous body mechanical properties successfully using inverse method, which provides a new method for identifying vitreous liquefactions related studies.

Opto-mechanical self-adjustment model of the human eye

The eye has specific optical and biomechanical properties that jointly regulate the eye's quality of vision, shape, and elasticity. These two characteristics are interdependent and correlated. Contrary to most currently available computational models of the human eye that only focus on biomechanical or optical aspects, the current study explores the inter-relationships between biomechanics, structure, and optical properties. Possible combinations of mechanical properties, boundary conditions, and biometrics were specified to ensure the opto-mechanical (OM) integrity to compensate for physiological changes in intraocular pressure (IOP) without compromising image acuity. This study evaluated the quality of the vision by analyzing the minimum spot diameters formed on the retina and drew how the self-adjustment mechanism affects the eye globe shape by adopting a finite element (FE) model of the eyeball. The model was verified by a water drinking test with biometric measurement (OCT Revo NX, Optopol) and tonometry (Corvis ST, Oculus).

The Roles of Vitreous Biomechanics in Ocular Disease, Biomolecule Transport, and Pharmacokinetics

PURPOSE

The biomechanical properties of the vitreous humor and replication of these properties to develop substitutes for the vitreous humor have rapidly become topics of interest over the last two decades. In particular, the behavior of the vitreous humor as a viscoelastic tissue has been investigated to identify its role in a variety of processes related to biotransport, aging, and age-related pathologies of the vitreoretinal interface.

METHODS

A thorough search and review of peer-reviewed publications discussing the biomechanical properties of the vitreous humor in both human and animal specimens was conducted. Findings on the effects of biomechanics on vitreoretinal pathologies and vitreous biotransport were analyzed and discussed.

RESULTS

The pig and rabbit vitreous have been found to be most mechanically similar to the human vitreous. Age-related liquefaction of the vitreous creates two mechanically unique phases, with an overall effect of softening the vitreous. However, the techniques used to acquire this mechanical data are limited by the in vitro testing methods used, and the vitreous humor has been hypothesized to behave differently in vivo due in part to its swelling properties. The impact of liquefaction and subsequent detachment of the vitreous humor from the posterior retinal surface is implicated in a variety of tractional pathologies of the retina and macula. Liquefaction also causes significant changes in the biotransport properties of the eye, allowing for significantly faster movement of molecules compared to the healthy vitreous. Recent developments in computational and ex vivo models of the vitreous humor have helped with understanding its behavior and developing materials capable of replacing it.

CONCLUSIONS

A better understanding of the biomechanical properties of the vitreous humor and how these relate to its structure will potentially aid in improving clinical metrics for vitreous liquefaction, design of biomimetic vitreous substitutes, and predicting pharmacokinetics for intravitreal drug delivery.

Explosive eye injuries: characteristics, traumatic mechanisms, and prognostic factors for poor visual outcomes

BACKGROUND

Explosions can produce blast waves, high-speed medium, thermal radiation, and chemical spatter, leading to complex and compound eye injuries. However, few studies have comprehensively investigated the clinical features of different eye injury types or possible risk factors for poor prognosis.

METHODS

We retrospectively reviewed all consecutive records of explosive eye injuries (1449 eyes in 1115 inpatients) in 14 tertiary referral hospitals in China over 12 years (between January 2008 and December 2019). Data on demographics, eye injury types, ocular findings, treatments, and factors affecting visual prognosis were extracted from a standardized database of eye injuries and statistically analyzed.

RESULTS

Mechanical ocular trauma accounted for 94.00% of explosion-related eye injuries, among which intraocular foreign bodies (IOFBs) resulted in 55.17% of open globe injuries (OGIs) and contusion caused 60.22% of close globe injuries (CGIs). Proliferative vitreous retinopathy (PVR) was more common in perforating (47.06%) and IOFB (26.84%) than in penetrating (8.79%) injuries, and more common with laceration (24.25%) than rupture (9.22%, P < 0.01). However, no difference was observed between rupture and contusion. Ultimately, 9.59% of eyes were removed and the final vision was ≤ 4/200 in 45.82% of patients. Poor presenting vision [odds ratio (OR) = 5.789], full-thickness laceration of the eyeball ≥ 5 mm (OR = 3.665), vitreous hemorrhage (OR = 3.474), IOFB (OR = 3.510), non-mechanical eye injury (NMEI, OR = 2.622, P < 0.001), rupture (OR = 2.362), traumatic optic neuropathy (OR = 2.102), retinal detachment (RD, OR = 2.033), endophthalmitis (OR = 3.281, P < 0.01), contusion (OR = 1.679), ciliary body detachment (OR = 6.592), zone III OGI (OR = 1.940), and PVR (OR = 1.615, P < 0.05) were significant negative predictors for poor visual outcomes.

CONCLUSIONS

Explosion ocular trauma has complex mechanisms, with multiple eyes involved and poor prognosis. In lethal level I explosion injuries, eyeball rupture is a serious condition, whereas contusion is more likely to improve. In level II injuries, IOFBs are more harmful than penetrating injuries, and level IV represents burn-related eye injuries. PVR is more associated with penetrating mechanisms than with OGI. Identifying the risk predictors for visual prognosis can guide clinicians in the evaluation and treatment of ocular blast injuries.

Rapid Prediction of Retina Stress and Strain Patterns in Soccer-Related Ocular Injury: Integrating Finite Element Analysis with Machine Learning Approach

Soccer-related ocular injuries, especially retinal injuries, have attracted increasing attention. The mechanics of a flying soccer ball have induced abnormally higher retinal stresses and strains, and their correlation with retinal injuries has been characterized using the finite element (FE) method. However, FE simulations demand solid mechanical expertise and extensive computational time, both of which are difficult to adopt in clinical settings. This study proposes a framework that combines FE analysis with a machine learning (ML) approach for the fast prediction of retina mechanics. Different impact scenarios were simulated using the FE method to obtain the von Mises stress map and the maximum principal strain map in the posterior retina. These stress and strain patterns, along with their input parameters, were used to train and test a partial least squares regression (PLSR) model to predict the soccer-induced retina stress and strain in terms of distributions and peak magnitudes. The peak von Mises stress and maximum principal strain prediction errors were 3.03% and 9.94% for the frontal impact and were 9.08% and 16.40% for the diagonal impact, respectively. The average prediction error of von Mises stress and the maximum principal strain were 15.62% and 21.15% for frontal impacts and were 10.77% and 21.78% for diagonal impacts, respectively. This work provides a surrogate model of FE analysis for the fast prediction of the dynamic mechanics of the retina in response to the soccer impact, which could be further utilized for developing a diagnostic tool for soccer-related ocular trauma.

Finite element method for estimation of applanation force and to study the influence of intraocular pressure of eye on tonometry

PURPOSE

Discover the associations of force of applanation on the eye with the plunging depth of the cornea and quantify them. The results will be utilized as the feedback parameter in the new prototype development of eye care instruments as additional force may damage the internal structure of the eye or may result in erroneous output.

METHOD

A finite element-based eye model is designed utilizing the actual dimensions of the human eye. A standardized tonometer is designed and the simulation is carried out at predetermined deformation of the cornea to find the force of applanation on the cornea during tonometry. Adding on, the influence of IOP during tonometry is analyzed for a range of plunging depths of the cornea.

RESULTS

The graphical results inferred the linear relation between the force of applanation with the deformation of the cornea and the results are quantified. The resulting deformation and stress plot of FEM based simulation approach is analyzed and observations regarding deformations and stress are made.

CONCLUSION

The human eye is successfully developed and also computed force on the cornea during tonometry is validated. The inference drawn from the deformation plot and stress plot is that the junction of cornea-sclera along with cornea-tonometer periphery undergo maximum deformation and experiences the highest stress compared to other areas of the eye while during tonometry.

Finite Element Analysis of Cornea and Lid Wiper during Blink, with and without Contact Lens

Ocular surface disorders such as Lid Wiper Epitheliopathy (LWE), Superior Epithelial Arcuate Lesion (SEAL), and contact lens-induced Limbal Stem Cell Deficiency (LSCD) as well as Superior Limbic Keratoconjunctivitis (SLK) affect one’s quality of life. Hence, it is imperative to investigate the underlying causes of these ocular surface disorders. During blink, the undersurface of the eyelid tends to interact with the cornea and the conjunctiva. The presence of a contact lens can add to the biomechanical frictional changes on these surfaces. To estimate these changes with and without a contact lens, a finite element model (FEM) of the eyelid wiper, eyeball, and contact lens was developed using COMSOL Multiphysics. Biomechanical properties such as von Mises stress (VMS) and displacement were calculated. Our study concluded that (a) maximum VMS was observed in the lid wiper in the absence of contact lens in the eye and (b) maximum VMS was observed in the superior 1.3 mm of the cornea in the presence of the contact lens in the eye. Thus, the development of friction-induced ocular surface disorders such as LWE, SLK, SEAL, and LSCD could be attributed to increased VMS. FEA is a useful simulation tool that helps us to understand the effect of blink on a normal eye with and without CL.

Two Years of Darkness: An Autobiographical Case Report of an Emergency Physician With Bilateral Retinal Detachments

Retinal detachments constitute an emergency ocular condition when the neurosensory retina separates from the retinal pigment epithelium, leading to the death of the tissue. Prompt diagnosis and treatment are essential to avoid significant morbidity, including vision loss and/or blindness associated with this condition. This case report describes the author’s challenging journey from a non-ophthalmologist perspective through the terrifying experience of bilateral rhegmatogenous retinal detachments involving seven surgical procedures prior to return to full clinical function.

Surgical outcomes and prognostic factors in traumatic retinal detachment following closed-globe injuries

PURPOSE

To evaluate the anatomical and functional results of retinal detachment (RD) surgery following closed-globe injuries (CGI).

METHODS

Patients treated with vitreoretinal surgeries due to RD following CGI from 2014 to 2020 were retrospectively reviewed. Data included demographics, mechanism of injury, preoperative evaluation, and surgical intervention. Outcome measurements included anatomic success, best corrected visual acuity (BCVA), and possible prognostic factors.

RESULTS

A total of 67 eyes from 64 patients (49 males; mean age 52.84 years) were included. The most common causes of the CGI were work-related injury (22.4%) and traffic accidents (23.9%). The primary and final anatomic success rates were 80.6% (54/67) and 89.6% (60/67), respectively. In the multivariable analysis of the logistic regression models, the poor prognostic factor was proliferative vitreoretinopathy (PVR) (P = 0.009) for primary anatomic success. The median preoperative and final BCVA were logMAR 0.7 (IQR, 0.3-1.6) and logMAR 0.5 (IQR, 0.1-1.1), respectively (P = 0.077). Poorly presenting BCVA (counting fingers or worse) and giant tear were associated with poor visual outcomes.

CONCLUSION

Work-related injuries and traffic accidents are the prevalent causes of RD following CGI. The anatomic outcomes were favorable, but visual outcomes varied. Poor prognostic factors included PVR and poorly presenting BCVA, highlighting the importance of a careful initial evaluation.

A study for lens capsule tearing during capsulotomy by finite element simulation

BACKGROUND AND OBJECTIVE

During capsulotomy, the force applied to the anterior capsule is a crucial parameter controlling capsule tears, that affects the clinical performance. This study aims to investigate the tear force in capsulotomy and analyze the effects of different tearing conditions on the tear force.

METHODS

A three-dimensional model of the human lens was constructed based on published clinical data using the finite element (FE) method. The lens model consisted of four layers: the anterior and posterior lens capsule, the cortex, and the nucleus. Distortion energy failure criterion combined with the bilinear interface law was used to express the crack propagation process at the edge of the anterior lens capsule. At the clamping position, a local coordinate system was established to parameterize the capsule tearing. The simulation results were then validated by conducting a capsulorhexis experiment using isolated porcine eyes with force-sensing forceps.

RESULTS

The simulation results showed a good agreement with the experimental data of two porcine specimens (No. 6 and 9) during a stable tearing process (p-values = 0.76 and 0.10). The mean force differences between the experimental data and the simulation were 3.10 ± 2.24 mN and 2.14 ± 1.73 mN, respectively. The tear direction with a minimum mean tear force was at θ₁ = 0° and θ₂ = 30°. The tear velocity was not significantly different to the variation in the tear force. However, an appropriate capsulorhexis diameter was found to contribute to the reduction of tear force.

CONCLUSIONS

The outcome of this paper demonstrates that our FE model could be used in modeling lens capsule tearing and the theoretical study of tear mechanism.

Experimental evaluation of the viscoelasticity of porcine vitreous

This study aims to estimate the material properties of the porcine vitreous while testing it in close to its natural physiological conditions. Eighteen porcine eyes were tested within 48 h post-mortem. A custom-built computer-controlled test rig was designed to support, load and monitor the behaviour of eye globes while being subjected to dynamic rotation cycles mimicking saccade eye movement. Specimens were glued to the base of a container, surrounded by gelatin, frozen and cut in half to expose the vitreous. After thawing, the container was subjected to concentric dynamic rotations of up to 5°, 10° or 15°, while taking 50 MP photos of the specimen every 2 ms. The images were analysed by a digital image correlation algorithm to trace the movement of marked points on the vitreous surface with different radii from the centre of the posterior chamber. The initial camera image was used in building a finite-element model of the test set-up, which was used in an inverse analysis exercise to estimate the material properties of the vitreous. Angular displacements of the monitored points were up to 3.3°, 4.1° and 3.9° in response to eye rotations of 5°, 10° and 15°, respectively. With the experimental relationships between eye rotation and angular displacements used as target behaviour, the inverse analysis exercise estimated the initial shear modulus, the long-term shear modulus and the viscoelastic decay constant of the porcine vitreous as 2.10 ± 0.15 Pa, 0.50 ± 0.04 Pa and 1.20 ± 0.09 s^-1, respectively. Consideration of the viscoelasticity of the vitreous was essential to represent its experimental behaviour. Testing the vitreous in close to its normal physiological conditions produced estimations of the initial shear modulus and long-term shear modulus that were, respectively, smaller and larger than reported values (Zimberlin et al. 2010 Soft Matter 6, 3632-3635. (doi:10.1039/b925407b), Liu et al. 2013 J. Biomech. 46, 1321-7. (doi:10.1016/j.jbiomech.2013.02.006), Rossi et al. 2011 Invest. Ophthalmol. Vis. Sci. 52, 3994-4002. (doi:10.1167/iovs.10-6477)).

The choroidal rupture: current concepts and insights

Choroidal rupture is a posterior segment affliction following a traumatic event that results in a break in the retinal pigment epithelium, Bruch membrane, and the underlying choriocapillaris. The visual prognosis may be extremely poor when involving the macular area or in cases with major comorbidities. On funduscopic examination the rupture appears as a whitish/yellowish curvilinear or crescent-shaped lesion with forked or tapered endings. Multimodal imaging including fluorescein angiography, indocyanine green angiography, optical coherence tomography, and optical coherence tomography angiography can provide a detailed assessment of the extent of damage and the onset of complications. Although there is no treatment for choroidal rupture per se, associated complications such as angle-recession glaucoma, retinal detachment, or exudative choroidal neovascularization might need therapeutic interventions. We describe the pathophysiology of choroidal rupture, the recent multimodal imaging findings, and the available treatment options for the management of complications.

Analysis of the effects of finite element type within a 3D biomechanical model of a human optic nerve head and posterior pole

BACKGROUND AND OBJECTIVE

Biomechanical stresses and strains can be simulated in the optic nerve head (ONH) using the finite element (FE) method, and various element types have been used. This study aims to investigate the effects of element type on the resulting ONH stresses and strains.

METHODS

A single eye-specific model was constructed using 3D delineations of anatomic surfaces in a high-resolution, fluorescent, 3D reconstruction of a human posterior eye, then meshed using our simple meshing algorithm at various densities using 4- and 10-noded tetrahedral elements, as well as 8- and 20-noded hexahedral elements. A mesh-free approach was used to assign heterogeneous, anisotropic, hyperelastic material properties to the lamina cribrosa, sclera and pia. The models were subjected to elevated IOP of 45 mmHg after pre-stressing from 0 to 10 mmHg, and solved in the open-source FE package Calculix; results were then interpreted in relation to computational time and simulation accuracy, using the quadratic hexahedral model as the reference standard.

RESULTS

The 10-noded tetrahedral and 20R-noded hexahedral elements exhibited similar scleral canal and laminar deformations, as well as laminar and scleral stress and strain distributions; the quadratic tetrahedral models ran significantly faster than the quadratic hexahedral models. The linear tetrahedral and hexahedral elements were stiffer compared to the quadratic element types, yielding much lower stresses and strains in the lamina cribrosa.

CONCLUSIONS

Prior studies have shown that 20-noded hexahedral elements yield the most accurate results in complex models. Results show that 10-noded tetrahedral elements yield very similar results to 20-noded hexahedral elements and so they can be used interchangeably, with significantly lower computational time. Linear element types did not yield acceptable results.

Case Report: Suprachoroidal Hemorrhage after Chiropractic Manipulation of the Neck

SIGNIFICANCE

The case report highlights the possible complications of undergoing neck manipulation within a critical time period after intravitreal injection.

PURPOSE

This study aimed to describe a case of traumatic hemorrhagic choroidal detachment after cervical manipulation during a chiropractic treatment session.

CASE REPORT

A 43-year-old male patient with a history of complex rhegmatogenous retinal detachment repair and recurrent cystoid macular edema presented with decreased vision and sudden pain in the right eye after chiropractic manipulation of the neck, status post-intravitreal injection of triamcinolone, which was performed earlier that day. Vision in the right eye was hand motion and 20/20 in the left eye. IOPs were 8 and 11 mmHg, respectively. Slit lamp examination of the right eye revealed blood-tinged steroid residues in the anterior chamber. There was no view to the posterior pole. Ultrasonography showed a lobulated mass with heterogeneous echogenicity consistent with a large hemorrhagic choroidal detachment. No central kissing was observed. Left eye examination was unremarkable.

CONCLUSIONS

With the increasing use of complementary and alternative medicine, a better understanding of potential complications to raise awareness is becoming essential.

Posterior pole retinal tears following blunt ocular trauma

Purpose

Posterior pole retinal tears occur rarely following blunt trauma. We describe a case of traumatic macular tears, without concurrent peripheral retinal tears or holes.

Observations

A 17-year-old patient presented to our emergency unit with blunt ocular trauma and multiple maxillofacial fractures after being assaulted. On examination visual acuity was 20/200 in the left eye with scant vitreous and preretinal hemorrhages. Funduscopic examination revealed multiple choroidal ruptures running concentrically to the optic disc, a subretinal macular hemorrhage, and a large macular tear in the area of the inferior vascular arcade just temporal to the macula. Optical coherence tomography revealed subretinal fluid in the foveal area, choroidal ruptures and a slight elevation of the macular retinal tear margins without subretinal fluid. Laser retinopexy was performed around the macular tear nasally. On follow-up, the retina in the lasered area remained flat, while a shallow retinal detachment had developed temporal to the tear, with a second tear appearing supero-temporally to the macula. Laser retinopexy was not possible due to surrounding subretinal hemorrhage. The clinical course was later complicated by macular detachment, necessitating pars plana vitrectomy with endolaser around the posterior tears and the retinal periphery, and silicone oil injection.

Conclusions

While traumatic macular holes and traumatic macular choroidal ruptures have both been extensively described, posterior pole and macular retinal tears following blunt trauma have rarely been reported. This case illustrates this unusual finding, discussing the possible pathogenic mechanisms and the importance of close follow-up of patients after blunt trauma with appropriate imaging.

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.

Computational modeling of blast induced whole-body injury: a review

Blast injuries affect millions of lives across the globe due to its traumatic after effects on the brain and the whole body. To date, military grade armour materials are designed to mitigate ballistic and shrapnel attacks but are less effective in resisting blast impacts. In order to improve blast absorption characteristics of armours, the first key step is thoroughly understands the effects of blasts on the human body itself. In the last decade, a plethora of experimental and computational work has been carried out to investigate the mechanics and pathophysiology of Traumatic Brain Injury (TBI). However, very few attempts have been made so far to study the effect of blasts on the various other parts of the body such as the sensory organs (eyes and ears), nervous system, thorax, extremities, internal organs (such as the lungs) and the skeletal system. While an experimental evaluation of blast effects on such physiological systems is difficult, developing finite element (FE) models could allow the recreation of realistic blast scenarios on full scale human models and simulate the effects. The current article reviews the state-of-the-art in computational research in blast induced whole-body injury modelling, which would not only help in identifying the areas in which further research is required, but would also be indispensable for understanding body location specific armour design criteria for improved blast injury mitigation.

Development of a finite-element eye model to investigate retinal hemorrhages in shaken baby syndrome

Retinal hemorrhages (RH) are among injuries sustained by a large number of shaken baby syndrome victims, but also by a small proportion of road accident victims. In order to have a better understanding of the underlying of RH mechanisms, we aimed to develop a complete human eye and orbit finite element model. Five occipital head impacts, at different heights and on different surfaces, and three shaking experiments were conducted with a 6-week-old dummy (Q0 dummy). This allowed obtaining a precise description of the motion in those two specific situations, which was then used as input for the eye model simulation. Results showed that four parameters (pressure, Von Mises stress and strain, 1st principal stress) are relevant for shaking-fall comparison. Indeed, in the retina, the softest shaking leads to pressure that is 4 times higher than the most severe impact (1.43 vs. 0.34 kPa). For the Von Mises stress, strain and 1st principal stress, this ratio rises to 4.27, 6.53 and 14.74, respectively. Moreover, regions of high stress and strain in the retina and the choroid were identified and compared to what is seen on fundoscopy. The comparison between linear and rotational acceleration in fall and shaking events demonstrated the important role of the rotational acceleration in inducing such injuries. Even though the eye model was not validated, the conclusion of this study is that compared to falls, shaking an infant leads to extreme eye loading as demonstrated by the values taken by the four mentioned mechanical parameters in the retina and the choroid.

Retinal Detachment Associated With Basketball-Related Eye Trauma

PURPOSE

Basketball is a popular sport involving significant body contact, which may frequently result in ocular trauma. The aim of this study was to evaluate the characteristics and visual outcomes of retinal detachment associated with basketball-related injury.

DESIGN

Retrospective, interventional case series.

METHODS

We reviewed the course of patients who sustained traumatic retinal detachment from basketball-related ocular trauma between 2003 and 2015.

RESULTS

Thirteen patients were evaluated for basketball-related traumatic retinal detachment. Twelve (92%) were male and 1 (8%) female, with an average age of 18.2 years. The majority (9 of 13, 70%) of patients had moderate-to-high myopia, and none were using protective eyewear when they sustained the eye trauma. Rhegmatogenous retinal detachment was observed in all eyes. The preoperative mean visual acuity was 20/625 (range, hand motions to 20/20). Initial surgery using scleral buckling alone was performed in most (8 of 13, 62%) of the patients. Retinal reattachment was achieved in 10 (76%) eyes after the first operation and in 12 (92%) at the end of the intervention. The mean follow-up was 3.9 years (range, 4 months to 12 years). The visual acuity during last follow-up was 20/231 (range, light perception to 20/20). In the multivariable analysis, initial visual acuity was an independent factor affecting the final visual outcome (P = .006).

CONCLUSION

Retinal detachment associated with basketball-related injury may cause severe visual loss. In the current study, all retinal detachments were of rhegmatogenous type and commonly occurred in young individuals with myopia. Initial visual acuity was associated with the prognosis. Risk awareness for early detection and intervention are important in these traumas.

SIMULATING THE EFFECTS OF ELEVATED INTRAOCULAR PRESSURE ON OCULAR STRUCTURES USING A GLOBAL FINITE ELEMENT MODEL OF THE HUMAN EYE

Elevated intraocular pressure (IOP) may be the primary risk factor to the development of glaucoma. Finite element (FE) modeling is commonly considered as an effective method to quantitatively analyze pathogenesis of glaucoma. Recent researches focus on establishing partial human eye models. A refined global human eye model was developed using ANSYS software to investigate the correlation between IOP elevation and biomechanical responses. First, the pressure transferring process according to IOP elevation in the whole eye was analyzed to simulate the effects of IOP elevation on glaucoma. Then, the biomechanical responses of the anterior eye segment under various pressure differences between the anterior and posterior chambers (AC and PC) were analyzed to simulate posterior nonadhesion of iris and posterior synechia. This global eye model not only simulated the responses of elevated IOP on ocular structures, but also revealed the process of pressure transferring among each tissue from the anterior eye segment to the optic nerve head (ONH) region. The local mechanical characteristics of the ocular structures obtained from the global model agreed with previous findings. This global model may shed light on the studies of multifactorial glaucoma.

FINITE ELEMENT ANALYSIS OF THE MECHANICAL CHARACTERISTICS OF GLAUCOMA

Purpose: Construct a finite element model of the human eye to quantitatively analyze the mechanical characteristics of the human eye, especially the glaucoma damage process of the optic nerve head (ONH). Method: First, the geometry model of the human eye with nonuniform thickness was established based on a reasonable hypothesis and assumptions. Because the ONH is an important factor for glaucoma, we refine the structure of the ONH with lamina cribrosa. Then, mesh division was applied for finite element analysis. To simplify the complexity of the analysis, the materials of the model were assumed to be isotropic linear elastic materials, and physical properties such as Young’s modulus and Poisson’s ratio were set according to published literature. Next, proper constraints and loads were applied to the model and solved with a finite element method. Result: A finite element model of the human eye was created to simulate the mechanical characteristics of the eye structures under high intraocular pressure (IOP). The ONH depressed 1.057[Formula: see text]mm under 0.009[Formula: see text]MPa pressure to simulate high IOP. Conclusion: The constructed model is able to quantitatively simulate excavation of the optic disc and damage of the optic nerve. The result proved Houcheng Liang’s hypothesis about the ONH damage mechanism in glaucoma.

A comparative study on dynamic stiffness in typical finite element model and multi-body model of C6-C7 cervical spine segment

In contrast to numerous researches on static or quasi-static stiffness of cervical spine segments, very few investigations on their dynamic stiffness were published. Currently, scale factors and estimated coefficients were usually used in multi-body models for including viscoelastic properties and damping effects, meanwhile viscoelastic properties of some tissues were unavailable for establishing finite element models. Because dynamic stiffness of cervical spine segments in these models were difficult to validate because of lacking in experimental data, we tried to gain some insights on current modeling methods through studying dynamic stiffness differences between these models. A finite element model and a multi-body model of C6-C7 segment were developed through using available material data and typical modeling technologies. These two models were validated with quasi-static response data of the C6-C7 cervical spine segment. Dynamic stiffness differences were investigated through controlling motions of C6 vertebrae at different rates and then comparing their reaction forces or moments. Validation results showed that both the finite element model and the multi-body model could generate reasonable responses under quasi-static loads, but the finite element segment model exhibited more nonlinear characters. Dynamic response investigations indicated that dynamic stiffness of this finite element model might be underestimated because of the absence of dynamic stiffen effect and damping effects of annulus fibrous, while representation of these effects also need to be improved in current multi-body model. Copyright © 2015 John Wiley & Sons, Ltd.

Simulations of Porcine Eye Exposure to Primary Blast Insult

PURPOSE

A computational model of the porcine eye was developed to simulate primary blast exposure. This model facilitates understanding of blast-induced injury mechanisms.

METHODS

A computational model of the porcine eye was used to simulate the effects of primary blast loading for comparison with experimental findings from shock tube experiments. The eye model was exposed to overpressure-time histories measured during physical experiments. Deformations and mechanical stresses within various ocular tissues were then examined for correlation with pathological findings in the experiments.

RESULTS

Stresses and strains experienced in the eye during a primary blast event increase as the severity of the blast exposure increases. Peak stresses in the model occurred in locations in which damage was most often observed in the physical experiments.

CONCLUSIONS

Blast injuries to the anterior chamber may be due to inertial displacement of the lens and ciliary body while posterior damage may arise due to contrecoup interactions of the vitreous and retina. Correlation of modeling predictions with physical experiments lends confidence that the model accurately represents the conditions found in the physical experiments.

TRANSLATIONAL RELEVANCE

This computational model offers insights into the mechanisms of ocular injuries arising due to primary blast and may be used to simulate the effects of new protective eyewear designs.

Traumatic retinal detachment--the difficulty and importance of correct diagnosis

Accurate characterization of a retinal detachment as traumatic is often difficult, but is important because it may instigate a careful search for occult coexistent traumatic pathology, affect the prognosis and the treatment of both eyes, influence insurance coverage benefits and medical-legal determinations, and is essential for epidemiologic studies. We review the epidemiology and pathophysiology of traumatic retinal detachment, common obstacles to correct diagnosis, diagnostic guidelines, and outline categories of traumatic causal relationships. Because there is no generally accepted definition of traumatic retinal detachment, we offer a practical one. Categorization as traumatic should be based on the particular history and physical examination rather than epidemiologic criteria.

Quantitative imaging of enzymatic vitreolysis-induced fiber remodeling

PURPOSE

Collagen fiber remodeling in the vitreous body has been implicated in cases of vitreomacular traction, macular hole, and retinal detachment, and also may occur during pharmacologic vitreolysis. The purpose of this study was to evaluate quantitative polarized light imaging (QPLI) as a tool for studying fiber organization in the vitreous and near the vitreoretinal interface in control and enzymatically perturbed conditions.

METHODS

Fiber alignment was measured in anterior-posterior sections of bovine and porcine vitreous. Additional tests were performed on bovine lenses and nasal-temporal vitreous sections. Effects of proteoglycan degradation on collagen fiber alignment using trypsin and plasmin were assessed at the microstructural level using electron microscopy and at the global level using QPLI.

RESULTS

Control vitreous showed fiber organization patterns consistent with the literature across multiple-length scales, including the global anterior-posterior coursing of vitreous fibers, as well as local fibers parallel to the equatorial vitreoretinal interface and transverse to the posterior interface. Proteoglycan digestion with trypsin or plasmin significantly increased fiber alignment throughout the vitreous (P < 0.01). The largest changes (3×) occurred in the posterior vitreous where fibers are aligned transverse to the posterior vitreoretinal interface (P < 0.01).

CONCLUSIONS

Proteoglycan loss due to enzymatic vitreolysis differentially increases fiber alignment at locations where tractions are most common. We hypothesize that a similar mechanism leads to retinal complications during age-related vitreous degeneration. Structural changes to the entire vitreous body (as opposed to the vitreoretinal interface alone) should be evaluated during preclinical testing of pharmacological vitreolysis candidates.