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

Long-term follow-up of a patient with partial optic nerve avulsion associated with submacular hemorrhage who underwent pneumatic displacement

Purpose

We report the case of a 16-year-old boy with partial optic nerve avulsion (ONA) and submacular hemorrhage (SMH) resulting from blunt ocular trauma who underwent pneumatic displacement and subsequent monitoring with optical coherence tomography (OCT) and fundus photography.

Observations

Reduced visual acuity was observed in the right eye at presentation (20/2400). Vitreous hemorrhage, partial ONA, and SMH were observed during dilated fundus examination. SMH was managed via pneumatic displacement. Subsequent examination revealed improvement in the visual acuity of the right eye with a substantial reduction in the subfoveal hemorrhage. Further improvement in visual acuity was observed 6 months after the injury (20/150). A smaller optic nerve head excavation defect, foveal atrophy, and reabsorption of SMH were observed during fundus examination. OCT of the optic nerve revealed that glial growth had covered the avulsion excavation. However, atrophy of the outer retinal layer of the fovea was observed during macular OCT.

Conclusions and importance

This case emphasizes the importance of performing multimodal imaging in cases of ONA as it enables the identification of alterations in the retinal layers and optic nerve. The subretinal hemorrhage was displaced from the subfoveal region without any adverse effects.

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.

Clinical profile and visual outcome in patients with traumatic optic neuropathy

Purpose

To analyze the visual outcome in patients with traumatic optic neuropathy (TON) with respect to different treatment modalities, to study the correlation of initial visual loss with the final visual outcome, and to find out the predictor of final visual outcome in patients with indirect TON.

Methods

A retrospective analysis of 36 eyes with TON was done. Data on clinical profile, including demographics, mode of trauma, best corrected visual acuity (BCVA), pupillary reflex examination, and anterior and posterior segment examination, was collected. Presence and location of orbital and cranial fractures were identified from computed tomography scan. Visual outcomes following steroid therapy, optic nerve (ON) decompression, and in untreated patients were analyzed. Pre- and post-treatment BCVA were divided into three groups based on logarithm of the minimum angle of resolution (logMAR) as follows: group A: 3, group B: 2.9-1.3, and group C<1.3. BCVA values at follow-up visits were taken as the primary outcome measure. Association between various risk factors and final visual outcome in patients with indirect TON was also analyzed.

Results

Out of 34 patients whose 36 eyes were studied, three (8.8%) patients were females and 31 (91.2%) patients were males. Most common mode of trauma was road traffic accident (RTA; 91.2%), which was followed by fall (8.8%) and assault (2.9%). Pre- and post-treatment BCVA values of 36 eyes were compared, and improvement in BCVA after treatment was found to be statistically significant. Also, 28.6% of patients with presenting BCVA of no light perception showed improvement compared to 94.1% and 100% in groups B and C, respectively. Orbital wall fractures were seen in 80.5% (n = 29) of the patients, with lateral wall fracture being the most common (58.3%) followed by medial wall (33.3%), roof (27.7%), floor (27.7%), and optic strut (5%).

Conclusion

Baseline BCVA had significant association with final vision improvement. Lateral wall fracture was the most common fracture associated with indirect TON. Patients treated with high-dose corticosteroids, irrespective of the time of presentation, had a better visual outcome.

Traumatic Optic Neuropathy: Update on Management

Traumatic optic neuropathy is one of the causes of visual loss caused by blunt or penetrating head trauma and is classified as both direct and indirect. Clinical history and examination findings usually allow for the diagnosis of traumatic optic neuropathy. There is still controversy surrounding the management of traumatic optic neuropathy; some physicians advocate observation alone, while others recommend steroid therapy, surgery, or both. In this entry, we tried to highlight traumatic optic neuropathy's main pathophysiologic mechanisms with the most available updated treatment. Recent research suggests future therapies that may be helpful in traumatic optic neuropathy cases.

Identification of optimal surgical plan for treatment of extraocular muscle damage in thyroid eye disease patients based on computational biomechanics

This study replicated the behavior of intraorbital tissue in patients with thyroid eye disease (TED) based on finite element analysis for general orbital decompression risk evaluation in thyroid eye disease patients. The orbit and intraorbital tissues of thyroid eye disease patients who underwent orbital decompression were modeled as finite element models. The stress was examined at specific locations of the removed orbital wall of a thyroid eye disease patient with undergone orbital decompression, and its variation was analyzed as a function of the shape and dimension (to be removed). As a result, in orbital decompression surgery which removes the orbital wall in a rectangular shape, the stress at the orbital wall decreased as the width and depth of the removed orbital wall increased. In addition, in the case of orbital decompression, it can be seen that the chamfered model compared to the non-chamfered model (a form of general orbital decompression) have the stress reduction rate from 11.08% to 97.88%. It is inferred that if orbital decompression surgery considering the chamfered model is performed on an actual thyroid eye disease patient, it is expected that the damage to the extraocular muscle caused by the removed orbital wall will be reduced.

FOCAL RETINAL ISCHEMIA REVEALED BY MULTIMODAL IMAGING AFTER TRAUMATIC PARTIAL OPTIC NERVE AVULSION

PURPOSE

Traumatic optic neuropathy can have varying presentations. Blunt focal trauma can lead to optic nerve avulsion with underlying retinal findings. A case of partial optic nerve avulsion after finger poke injury leading to focal retinal ischemia is reported.

METHODS

Visual acuity, fundus photography with fluorescein angiography, and spectral-domain optical coherence tomography were performed to document the findings in a 16-year-old man who presented after a finger poke injury to the left orbit during a water polo match.

RESULTS

On initial presentation, examination revealed decreased visual acuity with a fixed left pupil and afferent pupillary defect by reverse. On slit-lamp examination of the left eye, a hyphema was present. Dilated fundus examination revealed layering vitreous hemorrhage over the posterior pole and an avulsed vitreous base. On follow-up, a gap temporal to the optic nerve head consistent with a partial optic nerve avulsion was noted once the vitreous hemorrhage cleared. Multimodal imaging revealed retinal ischemia temporal to the disc on fluorescein angiography with corresponding changes in the inner retinal layers and retinal nerve fiber layer using spectral-domain optical coherence tomography.

CONCLUSION

Clinicians should have a high suspicion for optic nerve avulsion if a patient presents with new vitreous hemorrhage and afferent pupillary defect after a finger-poke injury. Optic nerve avulsion injury can cause retinal ischemia, likely because of interruption of retinal blood flow as a result of nerve shearing injury. Multimodal imaging can reveal focal retinal injury and aid in proper diagnosis and follow-up.

Effect of orbital volume in unilateral orbital fracture on indirect traumatic optic neuropathy

PURPOSE

This retrospective study aimed to analyze the relationship between the volume of the fractured and the normal orbit in patients with unilateral orbital fractures with and without indirect traumatic optic neuropathy (TON).

SUBJECTS

Data of 25 patients with unilateral orbital fractures who underwent computer tomography between January 2016 and December 2020 were investigated. Emergency imaging was performed within 2 hours of arrival at the emergency room. The subjects were categorized into two groups: unilateral orbital fractures with and without TON.

METHODS AND MEASURES

The assessment of TON was performed during a comprehensive ophthalmologic examination by an ophthalmologist. The stereographic orbit was reconstructed, and the volume was calculated. Other variables examined included age, sex, and cause of orbital trauma. The variables were compared using paired t-tests. Statistical significance was set at p < 0.05.

RESULTS

The orbital volume of the non-fractured orbit was 27.50  ± 2.26 and 27.48  ±  2.64 cm³ in the groups with and without TON, respectively. The average volume of the fractured orbit in the TON group was 27.78  ± 2.56 cm³, and there was no significant volumetric difference between the fractured and non-fractured sides in this group. However, the average volume of the fractured orbit without TON was 28.76  ±  3.18 cm³, larger than that of the non-fractured orbit (p = 0.016).

CONCLUSIONS

Non-expansion of the fractured orbit was a risk factor for indirect TON in patients with unilateral orbital fractures. Volumetric analysis from primary imaging would expedite the diagnosis and treatment of TON, resulting in optimal outcomes.

Case report: Partial visual recovery from incomplete traumatic optic nerve avulsion caused by a badminton shuttle

Purpose

Blunt ocular trauma rarely results in optic nerve avulsion. Here, we report a case of incomplete optic nerve avulsion caused by the impact of a badminton shuttlecock.

Observations

The patient was a 16-year-old healthy male. A badminton shuttlecock hit his right eye from a short distance. On his first visit to the local eye clinic, his visual acuity in the right eye was hand motion. About 4-mm hyphema in height was observed in the right eye. Three days after the injury, visual acuity improved to 20/50, but the intraocular pressure increased to 40 mmHg; hence, intraocular pressure (IOP)-lowering medication was initiated. Five days after the injury, although hyphema had decreased gradually, he noticed a worsening of vision and was referred to our department. In his right eye, visual acuity was reduced to finger-counting, IOP was 38 mmHg. Slit-lamp examination of the right eye revealed a dilated pupil, hyphema, and angle recession. Fundus examination revealed dilation of the central retinal vein and edematous changes around the optic nerve head. Optical coherence tomography showed a very deep depression of the optic nerve head and partial rupture of the optic nerve axons. B-mode ultrasonography showed hypolucency just posterior to the optic nerve head. Goldmann perimetry revealed a central visual field defect in the right eye. Computed tomography showed no signs of optic canal fracture. These findings suggest that incomplete optic nerve avulsion had occurred. We performed IOP-lowering and anti-inflammatory therapy. After treatment, visual acuity was restored to 20/50, and the deep depression of the optic nerve head recovered to an almost normal range.

Conclusion and Importance

It was assumed that the impact of the badminton shuttlecock caused irreversible changes in the optic nerve head, but the visual function partially improved with IOP-lowering and anti-inflammatory therapy. Because eye injury in badminton can cause severe damage to visual function, every badminton player needs to wear an appropriate eye shield, and rules or guidelines to prevent untoward accidents are needed in badminton.

Diversified Treatment Options of Adult Stem Cells for Optic Neuropathies

Optic neuropathies refer to a group of ocular disorders with abnormalities or dysfunction of the optic nerve, sharing a common pathophysiology of retinal ganglion cell (RGC) death and axonal loss. RGCs, as the retinal neurons in the central nervous system, show limited capacity in regeneration or recovery upon diseases or after injuries. Critically, there is still no effective clinical treatment to cure most types of optic neuropathies. Recently, stem cell therapy was proposed as a potential treatment strategy for optic neuropathies. Adult stem cells, including mesenchymal stem cells and hematopoietic stem cells, have been applied in clinical trials based on their neuroprotective properties. In this article, the applications of adult stem cells on different types of optic neuropathies and the related mechanisms will be reviewed. Research updates on the strategies to enhance the neuroprotective effects of human adult stem cells will be summarized. This review article aims to enlighten the research scientists on the diversified functions of adult stem cells and consideration of adult stem cells as a potential treatment for optic neuropathies in future clinical practices.

A Finite Element Analysis Model is Suitable for Biomechanical Analysis of Orbital Development

ABSTRACT

The authors investigated orbital bone development in congenital microphthalmia (CM) using a three-dimensional finite element analysis model, after the orbital dimension deficiency was improved with a self-inflating hydrogel expander implant.Data of a 2-year-old male CM patient were examined. The orbital structure, eyeball, eye muscles, and self-inflating hydrogel expander were constructed according to computed tomography examination data. The effects of self-expanding spherical hydrogel at various locations in the muscle cone on orbital bone development were examined using 3-mL self-expanding expanders placed at shallow (model 1: 2 mm depth) and deep (model 2: 8 mm depth) muscle cone positions. This model simulated the hydrogel expansion process; the orbital bone biomechanics and radial displacement nephograms were obtained when the hydrogel volume increased 3, 5, 7, and 9 times and analyzed.The orbital bone biomechanics were concentrated at the medial orbital wall center, gradually spreading to the whole orbital wall. Biomechanics and radial displacement of the inferior temporal and lateral distal orbital wall region were the most significant, and were more significant in model 1 than in model 2.Finite element analysis is suitable for the biomechanical analysis of orbital development in CM. The shallow position inside CM patients' muscle cone is the optimal site for hydrogel implantation.

Afferent Visual Manifestations of Traumatic Brain Injury

Traumatic brain injury (TBI) causes structural and functional damage to the central nervous system including the visual pathway. Defects in the afferent visual pathways affect visual function and in severe cases cause complete visual loss. Visual dysfunction is detectable by structural and functional ophthalmic examinations that are routine in the eye clinic, including examination of the pupillary light reflex and optical coherence tomography (OCT). Assessment of pupillary light reflex is a non-invasive assessment combining afferent and efferent visual function. While a assessment using a flashlight is relatively insensitive, automated pupillometry has 95% specificity and 78.1% sensitivity in detecting TBI-related visual and cerebral dysfunction with an area under the curve of 0.69-0.78. OCT may also serve as a noninvasive biomarker of TBI severity, demonstrating changes in the retinal ganglion cell layer and nerve fiber layer throughout the range of TBI severity even in the absence of visual symptoms. This review discusses the impact of TBI on visual structure and function.

The Role of the Flash Visual Evoked Potential in Evaluating Visual Function in Patients with Indirect Traumatic Optic Neuropathy

Purpose

To assess the value of the flash visual evoked potential (FVEP) in determining final visual prognosis in patients with indirect traumatic optic neuropathy (TON).

Subjects and Methods

We included 30 patients diagnosed with indirect TON. Within one week of the onset of the trauma, visual acuity was recorded, pupillary reactions were assessed, FVEP was performed in both eyes. The amplitudes (N1p1 and N2P2) and the latency of P2 for each eye were recorded and amplitude ratio of N2P2 between the affected and normal eye was calculated. In follow-up visits, the cases underwent a complete ophthalmic examination, assessment of visual acuity, pupillary reaction, and FVEP.

Results

The study included 22 males (73.3%) and 8 females (26.7%). The right eye was involved in 16 patients (53.3%) and left eye was involved in 14 cases (46.7%). According to the findings of FVEP, there was a direct correlation between final visual acuity and initial amplitude of N1p1 and N2P2 and negative correlation with latency of P2 wave. In 20 patients in whom the N1P1 and N2P2 amplitude was within the normal range and amplitude ratio of N2P2 of normal and fellow eye was at least 0.5 and the P2 implicit time was less than 140 ms, they achieved better visual outcome and visual acuity improved in the affected eye. In other 10 patients in whom the N1P1 and N2P2 amplitude was below normal range and the N2P2 amplitude ratio between the normal and the affected eye was less than 0.5 and the P2 implicit time was more than 140 ms, the visual acuity in the affected eye was less than 0.01 and these patients achieved less or no improvement in their visual function.

Conclusion

Cases with TON usually present with severe loss of vision. FVEP is highly predictive of final visual outcome in patients having indirect TON given that the other eye is normal to be used as the patients’ internal control. More studies are needed to confirm these results.

Traumatic Optic Neuropathy

A host of different types of direct and indirect, primary and secondary injuries can affect different portions of the optic nerve(s). Thus, in the setting of penetrating as well as nonpenetrating head or facial trauma, a high index of suspicion should be maintained for the possibility of the presence of traumatic optic neuropathy (TON). TON is a clinical diagnosis, with imaging frequently adding clarification to the full nature/extent of the lesion(s) in question. Each pattern of injury carries its own unique prognosis and theoretical best treatment; however, the optimum management of patients with TON remains unclear. Indeed, further research is desperately needed to better understand TON. Observation, steroids, surgical measures, or a combination of these are current cornerstones of management, but statistically significant evidence supporting any particular approach for TON is absent in the literature. Nevertheless, it is likely that novel management strategies will emerge as more is understood about the converging pathways of various secondary and tertiary mechanisms of cell injury and death at play in TON. In the meantime, given our current deficiencies in knowledge regarding how to best manage TON, "primum non nocere" (first do no harm) is of utmost importance.

A Systematic Literature Review on Traumatic Optic Neuropathy

Traumatic optic neuropathy (TON) is an uncommon vision-threatening disorder that can be caused by ocular or head trauma and is categorized into direct and indirect TON. The overall incidence of TON is 0.7–2.5%, and indirect TON has a higher prevalence than direct TON. Detection of an afferent pupillary defect in the presence of an intact globe in a patient with ocular or head trauma with decreased visual acuity strongly suggests TON. However, afferent pupillary defects may be difficult to detect in patients who have received narcotics that cause pupillary constriction and in those with bilateral TON. Mechanical shearing of the optic nerve axons and contusion necrosis due to immediate ischemia from damage to the optic nerve microcirculation and apoptosis of neurons is a probable mechanism. The proper management of TON is controversial. High-dose corticosteroid therapy and decompression of the optic nerve provide no additional benefit over observation alone. Intravenous erythropoietin may be a safe and efficient treatment for patients with TON.

Gaze-evoked deformations of the optic nerve head in thyroid eye disease

PURPOSE

To assess gaze evoked deformations of the optic nerve head (ONH) in thyroid eye disease (TED), using computational modelling and optical coherence tomography (OCT).

METHODS

Multiple finite element models were constructed: one model of a healthy eye, and two models mimicking effects of TED; one with proptosis and another with extraocular tissue stiffening. Two additional hypothetical models had extraocular tissue softening or no extraocular tissue at all. Horizontal eye movements were simulated in these models. OCT images of the ONH of 10 healthy volunteers and 1 patient with TED were taken in primary gaze. Additional images were recorded in the same subjects performing eye movements in adduction and abduction. The resulting ONH deformation in the models and human subjects was measured by recording the 'tilt angle' (relative antero-posterior deformation of the Bruch's membrane opening).

RESULTS

In our computational models the eyes with proptosis and stiffer extraocular tissue had greater gaze-evoked deformations than the healthy eye model, while the models with softer or no extraocular tissue had lesser deformations, in both adduction and abduction. In healthy subjects, the mean tilt angle was 1.46°±0.25 in adduction and -0.42°±0.12 in abduction. The tilt angle measured in the subject with TED was 5.37° in adduction and -2.21° in abduction.

CONCLUSION

Computational modelling and experimental observation suggest that TED can cause increased gaze-evoked deformations of the ONH.

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.

A case report of unrecovered monocular vision loss after anterior clinoid mucocele resection

Purpose

To describe a patient of anterior clinoid mucocele presenting with orbital apex syndrome and to propose the reason for her unrecovered monocular vision loss after operation, we hope this case report can provide treatment experience for the similar rare disease.

Conclusions and Importance

Mucocele of the anterior clinoid process remains a rare cause of optic neuropathy. They usually present with acute, rapidly progressive, painless monocular visual loss. Urgent surgical decompression play a vital role in the recovery of neurological function.

An evolving perspective of endoscopic transnasal optic canal decompression for traumatic optic neuropathy in clinic

Traumatic optic neuropathy (TON) is a serious complication of craniofacial trauma, which damages the optic nerve indirectly and leads to dysfunction of visual acuity. The clinical intervention for a patient with TON includes optic canal decompression (with or without steroids), treatment with corticosteroids alone, or observation only. Currently, there is a controversy among clinicians as to which treatment is optimal. An increasing number of retrospective studies have unveiled that patients could experience significant improvement in visual acuity after optic canal decompression surgery, particularly endoscopic transnasal/transethmosphenoid optic canal decompression (ETOCD), either with or without corticosteroids. In this review, we discuss the evolving perspective on surgical treatment, specifically ETOCD, for the management of patients with TON and focus mainly on the therapeutic efficacy, safety, and resulting prognosis in the clinic.

Clinical treatment of traumatic optic neuropathy in children: Summary of 29 cases

Clinical features and treatments for traumatic optic neuropathy (TON) in children are reported. Twenty-nine children were enrolled in the Affiliated Hospital of Qingdao University from April 1999 to May 2015 for retrospective analysis. Of these 29 patients, 5 received drug therapy, and 24 received drug therapy combined with surgical therapy. Among the patients who received surgical therapy, 23 received nasal endoscopic optic decompression under general anaesthesia, and 1 received nasal endoscopic orbital decompression under general anaesthesia. All the patients were followed up for at least 6 months. In 29 cases, 48.28% (14/29) had visual improvement. Of the 5 patients who received drug therapy, 3 showed improvement (60%). Of the 24 cases who received drug and surgical therapy, 11 showed improvement (45.83%). Of the 22 patients who lost visual sensitivity, 10 showed improvement (45.45%). Of the 7 cases with visual acuity above basic light sensitivity, 4 showed improvement (57.14%). In conclusion, TON in children can lead to poor diagnosis and prognosis because of the difficulty of examining children and their limited language expression ability. Early ophthalmologic examination is therefore essential for children with craniofacial injuries, and proper treatment should be undertaken as soon as possible.

Risk Factor Analysis for the Outcomes of Indirect Traumatic Optic Neuropathy with No Light Perception at Initial Visual Acuity Testing

BACKGROUND

The optimal management of indirect traumatic optic neuropathy (TON) is controversial. We aimed to compare the differences in visual improvement by treatment option in patients presenting with TON and no light perception (NLP). We also wanted to identify any patient-related factors that might favor the use of steroid pulse therapy or optic nerve decompression (OND).

METHODS

We retrospectively identified 46 consecutive patients with indirect TON treated at Chang Gung Memorial Hospital between 2007 and 2015. The outcome was the improvement in visual acuity by improvement rate and degree of improvement.

RESULTS

Females had a better improvement rate than did males. Compared with delayed treatment, patients receiving steroid pulse therapy within 14 hours or receiving OND within 26 hours had a better improvement rate/degree. In patients with an initial intraocular pressure (IOP) of 17-23 mm Hg, the improvement rate/degree was significantly better than for patients with an IOP outside this range. For patients treated by OND, an initially normal IOP (11-21 mm Hg) suggested a significantly better prognosis in the improvement rate/degree.

CONCLUSIONS

For patients with indirect TON, initial NLP implies a poor prognosis, but steroid pulse therapy or OND are both feasible treatment options. These results emphasize the importance of timely treatment for patients with indirect TON and NLP. Females and patients with an initial IOP of 17-23 mm Hg were more likely to recover. The results of our study indicate that normal initial IOP (11-21 mm Hg) is good prognostic factor for patients with indirect TON treated with OND.

Biomechanical Evaluations of Ocular Injury Risk for Blast Loading

Ocular trauma is one of the most common types of combat injuries resulting from the exposure of military personnel with improvised explosive devices. The injury mechanism associated with the primary blast wave is poorly understood. We employed a three-dimensional computational model, which included the main internal ocular structures of the eye, spatially varying thickness of the cornea-scleral shell, and nonlinear tissue properties, to calculate the intraocular pressure and stress state of the eye wall and internal ocular structure caused by the blast. The intraocular pressure and stress magnitudes were applied to estimate the injury risk using existing models for blunt impact and blast loading. The simulation results demonstrated that blast loading can induce significant stresses in the different components of the eyes that correlate with observed primary blast injuries in animal studies. Different injury models produced widely different injury risk predictions, which highlights the need for experimental studies evaluating mechanical and functional damage to the ocular structures caused by the blast loading.

Optic Nerve Avulsion After Finger-Poke Injury

We present a case of optic nerve avulsion as a result of finger-poke injury to the eye. Spectral domain optical coherence tomography demonstrated a plunging cup indicative of the avulsion, a finding not previously described. Optic nerve avulsion is a form of anterior indirect traumatic optic neuropathy evoked by a sudden severe rotation at the junction of the optic nerve and globe induced, in this case, by penetration of the finger into the nasal orbit.

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.

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.

Blunt forehead trauma and optic canal involvement: finite element analysis of anterior skull base and orbit on causes of vision impairment

BACKGROUND

Clinical studies report on vision impairment after blunt frontal head trauma. A possible cause is damage to the optic nerve bundle within the optic canal due to microfractures of the anterior skull base leading to indirect traumatic optic neuropathy.

METHODS

A finite element study simulating impact forces on the paramedian forehead in different grades was initiated. The set-up consisted of a high-resolution skull model with about 740 000 elements, a blunt impactor and was solved in a transient time-dependent simulation. Individual bone material parameters were calculated for each volume element to increase realism.

RESULTS

Results showed stress propagation from the frontal impact towards the optic foramen and the chiasm even at low-force fist-like impacts. Higher impacts produced stress patterns corresponding to typical fracture patterns of the anterior skull base including the optic canal. Transient simulation discerned two stress peaks equalling oscillation.

CONCLUSIONS

It can be concluded that even comparatively low stresses and oscillation in the optic foramen may cause micro damage undiscerned by CT or MRI explaining consecutive vision loss. Higher impacts lead to typical comminuted fractures, which may affect the integrity of the optic canal. Finite element simulation can be effectively used in studying head trauma and its clinical consequences.

Traumatic optic neuropathy: a review

The aim of this article is to evaluate current literature on investigation and management of traumatic optic neuropathy (TON), propose recommendations for diagnosis and management, and explore novel future treatments. TON, though uncommon, causes substantial visual loss. Without clear guidelines, there is much ambiguity regarding its diagnosis and management. Investigation and treatment (conservative, medical, surgical, and combined) vary widely between centers. Electronic databases PubMed, MEDLINE, PROSPERO, CENTRAL, and EMBASE were searched for content that matched "Traumatic optic neuropathy." Articles with abstracts and full text available, published in the past 10 years, written English and limited to human adults, were selected. All study designs were acceptable except case reports and case series with fewer 10 patients. All abstracts were then evaluated for relevance. References of these studies were evaluated and if also relevant, included. A total of 2,686 articles were retrieved and 43 examined for relevance. Of these, 23 articles were included. TON is a clinical diagnosis. Visual-evoked potential is useful in diagnosis and prognosis. Computed tomography demonstrates canal fractures and concomitant injuries. Magnetic resonance images should be reserved for select and stable patients. Conservative treatment is appropriate in mild TON. Steroids are of questionable benefit and may be harmful. Surgery should be reserved for patients with radiological evidence of compression and individualized.

Space physiology IV: mathematical modeling of the cardiovascular system in space exploration

Mathematical modeling represents an important tool for analyzing cardiovascular function during spaceflight. This review describes how modeling of the cardiovascular system can contribute to space life science research and illustrates this process via modeling efforts to study postflight orthostatic intolerance (POI), a key issue for spaceflight. Examining this application also provides a context for considering broader applications of modeling techniques to the challenges of bioastronautics. POI, which affects a large fraction of astronauts in stand tests upon return to Earth, presents as dizziness, fainting and other symptoms, which can diminish crew performance and cause safety hazards. POI on the Moon or Mars could be more critical. In the field of bioastronautics, POI has been the dominant application of cardiovascular modeling for more than a decade, and a number of mechanisms for POI have been investigated. Modeling approaches include computational models with a range of incorporated factors and hemodynamic sophistication, and also physical models tested in parabolic and orbital flight. Mathematical methods such as parameter sensitivity analysis can help identify key system mechanisms. In the case of POI, this could lead to more effective countermeasures. Validation is a persistent issue in modeling efforts, and key considerations and needs for experimental data to synergistically improve understanding of cardiovascular responses are outlined. Future directions in cardiovascular modeling include subject-specific assessment of system status, as well as research on integrated physiological responses, leading, for instance, to assessment of subject-specific susceptibility to POI or effects of cardiovascular alterations on muscular, vision and cognitive function.

Modelling human eye under blast loading

Primary blast injury (PBI) is the general term that refers to injuries resulting from the mere interaction of a blast wave with the body. Although few instances of primary ocular blast injury, without a concomitant secondary blast injury from debris, are documented, some experimental studies demonstrate its occurrence. In order to investigate PBI to the eye, a finite element model of the human eye using simple constitutive models was developed. The material parameters were calibrated by a multi-objective optimisation performed on available eye impact test data. The behaviour of the human eye and the dynamics of mechanisms occurring under PBI loading conditions were modelled. For the generation of the blast waves, different combinations of explosive (trinitrotoluene) mass charge and distance from the eye were analysed. An interpretation of the resulting pressure, based on the propagation and reflection of the waves inside the eye bulb and orbit, is proposed. The peculiar geometry of the bony orbit (similar to a frustum cone) can induce a resonance cavity effect and generate a pressure standing wave potentially hurtful for eye tissues.

Optical coherence tomography in optic nerve head avulsion

Early diagnosis of optic nerve head (ONH) avulsion may be difficult due to an obscured fundus view. Although B-scan ultrasonography is more useful than MRI and CT imaging, it has limited sensitivity and specificity. Optical coherence tomography (OCT) can be used to identify optic nerve pathology. Utilization of OCT has not been widely reported in the diagnosis of ONH avulsion. Two cases OCT use in ONH avulsion are reported. The utility of OCT in the diagnosis of ONH avulsion is of limited value.

Closed incision management with negative pressure wound therapy (CIM): biomechanics

A novel closed incision management with negative pressure wound therapy (CIM) has been developed for convenient use with closed incisions that has the potential to be beneficial for patients at risk for postoperative complications. Incisions are typically under lateral tension. This study explored the biomechanical mechanisms by which integrity of the incisional closure is enhanced by CIM. CIM was hypothesized to affect local stresses around closed incisions in a beneficial manner. Finite element analyses (FEA) indicated that application of CIM decreased the lateral stresses ~50% around the incision and changed the direction of the stresses to a distribution that is typical of intact tissue. Bench evaluations corroborated findings that CIM significantly increased the force required to disrupt the closed incision by ~50% as compared with closure alone. In conclusion, using 2 FEAs and bench modeling, CIM was shown to reduce and normalize tissue stresses and bolster appositional forces at the incision.

Mechanical Properties of Orbital Fat and Its Encapsulating Connective Tissue

There is an increasing need to understand the mechanical properties of human orbital fat and its encapsulating connective tissue (OFCT), but such knowledge is not available in the current literature. The purpose of the present study is to examine the mechanical properties of the OFCT. From 5 pairs of 76- to 92-year-old Caucasian human eyes and 33 5- to 7-month-old porcine eyes, 5 human and 11 porcine OFCT samples were dissected at the posterior pole or adjacent to the pole in the vertical, horizontal, and radial directions. Sample dimensions were fixed or measured. Tensile tests were performed on the samples in body-temperature saline. The stress-strain relationship was first approximately linear and then became nonlinear. The linear, the neo-Hookean, and the Mooney–Rivlin constants are reported in Tables 1 and 2. No statistical difference was found among their properties in the different directions in either the human or the porcine samples. Statistical differences were found between the human and the porcine material constants in the horizontal and radial directions. Among our material models, only the Mooney–Rivlin model was able to capture the mechanical properties of the OFCT in large deformation properly. The Mooney–Rivlin model was especially adaptive to the human data. This is the first time the mechanical properties of the human and porcine OFCT have been examined in the literature. We believe our data will provide valuable information to others regarding designing implant biomaterials in orbital treatments and developing computer models to study orbital biomechanics.

Traumatic optic neuropathy: an evolving understanding

PURPOSE

To critically review the treatment of traumatic optic neuropathy.

DESIGN

A perspective of clinical and basic science studies related to traumatic optic neuropathy and its treatment.

METHODS

Published clinical and basic science studies on traumatic optic neuropathy were critically reviewed and interpreted.

RESULTS

Clinical progress in the treatment of traumatic optic neuropathy is limited by small clinical studies lacking appropriate control groups. The Corticosteroid Randomization for Acute Head Trauma (CRASH) trial found an increased rate of death among patients with acute head trauma treated with high-dose corticosteroids compared to placebo-treated patients (21% vs 18%, P = .0001). Recent animal studies also suggest that high-dose corticosteroids are toxic to the injured optic nerve.

CONCLUSIONS

The Corticosteroid Randomization for Acute Head Trauma study is immediately relevant to the treatment of traumatic optic neuropathy as individuals with traumatic optic neuropathy often have concomitant head trauma. High-dose corticosteroids for traumatic optic neuropathy will result in a measurable loss of life in patients who also have a brain injury. Death has never been an endpoint for traumatic optic neuropathy studies. Given human and animal data suggesting that treatment is harmful and the lack of demonstrated clinical efficacy, corticosteroids should not be used to treat traumatic optic neuropathy. The benefit of optic canal decompression is also unclear. There is a need to identify traumatic optic neuropathy soon after injury to further define the natural history of this injury. This information will provide a basis for assessing potential future treatments for traumatic optic neuropathy.

Functional and structural analysis of partial optic nerve avulsion due to blunt trauma: case report

Partial optic nerve avulsion (ONA) secondary to finger gouging is an uncommon but devastating injury. A 21-year-old man who had an acute vision loss after accidentally getting poked by himself in his right eye when he fell down during jogging is reported. The patient was diagnosed with partial ONA. Magnetic resonance imaging revealed intact optic nerve. Optical coherence tomography (OCT) revealed deep cavity at the inferior-temporal half of the optic disc. Retinal nerve fiber layer thickness was also thin at the inferior quadrant with circumpapillary OCT scan. Visual field test and electrophysiological tests showed functional abnormality compatible with optic nerve lesion. Diagnostic tools for anatomical and functional evaluation may reveal the course of this 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.

Elastic properties of porcine ocular posterior soft tissues

We examine the thickness and mechanical properties of the porcine posterior retina, choroid, and sclera in different environments and surface directions. Vertical and horizontal samples were surgically obtained. Uniaxial experiments were performed in room-temperature air, room-temperature saline, and body-temperature saline. Sample thicknesses were estimated optically. Thickness of all layers was found to vary significantly among the samples; thickness standard deviation of the mean was 24, 19, and 19% for the retina, choroid, and sclera, respectively. Transition stresses and heel moduli of all layers were consistently higher in saline than air. The retinal stress-strain relationship in air was typically linear with significantly lower horizontal transition strain. Transition stresses and moduli of all layers were consistently lower in body than room temperature and the differences in the transition stresses and heel moduli of the retina and sclera were significant. Also, the sclera had significantly lower transition strains in body temperature. These results illustrate the importance of testing the tissues at conditions like those found in the body. In body-temperature saline, all layers behaved nonlinearly, but only the retina exhibited surface anisotropy between the vertical and horizontal directions.

Modeling individual-specific human optic nerve head biomechanics. Part I: IOP-induced deformations and influence of geometry

Glaucoma, the second most common cause of blindness worldwide, is an ocular disease characterized by progressive loss of retinal ganglion cell (RGC) axons. Biomechanical factors are thought to play a central role in RGC loss, but the specific mechanism underlying this disease remains unknown. Our goal was to characterize the biomechanical environment in the optic nerve head (ONH)--the region where RGC damage occurs--in human eyes. Post mortem human eyes were imaged, fixed at either 5 or 50 mmHg pressure and processed histologically to acquire serial sections through the ONH. Three-dimensional models of the ONH region were reconstructed from these sections and embedded in a generic scleral shell to create a model of an entire eye. We used finite element simulations to quantify the effects of an acute change in intraocular pressure from 5 to 50 mmHg on the ONH biomechanical environment. Computed strains varied substantially within the ONH, with the pre-laminar neural tissue and the lamina cribrosa showing the greatest strains. The mode of strain having the largest magnitude was third principal strain (compression), reaching 12-15% in both the lamina cribrosa and the pre-laminar neural tissue. Shear strains were also substantial. The distribution of strains in all ONH tissues was remarkably similar between eyes. Inter-individual variations in ONH geometry (anatomy) have only modest effects on ONH biomechanics, and may not explain inter-individual susceptibility to elevated intraocular pressure. Consistent with previous results using generic ONH models, the displacements of the vitreo-retinal interface and the anterior surface of the lamina cribrosa can differ substantially, suggesting that currently available optical imaging methods do not provide information of the acute deformations within ONH tissues. Predicted strains within ONH tissues are potentially biologically significant and support the hypothesis that biomechanical factors contribute to the initial insult that leads to RGC loss in glaucoma.