Protective ocular mechanisms in woodpeckers

Minireview: Insights into the role of TRP channels in the retinal circulation and function

Consistent with their wide distribution throughout the CNS, transcripts of all transient receptor potential (TRP) cation channel superfamily members have been detected in both neuronal and non-neuronal cells of the mammalian retina. Evidence shows that members of the TRPC (canonical, TRPC1/4/5/6), TRPV (vanilloid, TRPV1/2/4), TRPM (melastatin, TRPM1/2/3/5), TRPA (ankyrin, TRPA1), and TRPP (polycystin, TRPP2) subfamilies contribute to retinal function and circulation in health and disease, but the relevance of most TRPs has yet to be determined. Their principal role in light detection is far better understood than their participation in the control of intraocular pressure, retinal blood flow, oxidative stress, ion homeostasis, and transmitter signaling for retinal information processing. Moreover, if the therapeutic potential of targeting some TRPs to treat various retinal diseases remains speculative, recent studies highlight that vision restoration strategies are very likely to benefit from the thermo- and mechanosensitive properties of TRPs. This minireview focuses on the evidence of the past 5 years about the role of TRPs in the retina and retinal circulation, raises some possibilities about the function of TRPs in the retina, and discusses the potential sources of endogenous stimuli for TRPs in this tissue, as a reflection for future studies.

Investigating the Effects of Mechanical Stimulation on Retinal Ganglion Cell Spontaneous Spiking Activity

Mechanical forces are increasingly recognized as major regulators of several physiological processes at both the molecular and cellular level; therefore, a deep understanding of the sensing of these forces and their conversion into electrical signals are essential for studying the mechanosensitive properties of soft biological tissues. To contribute to this field, we present a dual-purpose device able to mechanically stimulate retinal tissue and to record the spiking activity of retinal ganglion cells (RGCs). This new instrument relies on combining ferrule-top micro-indentation, which provides local measurements of viscoelasticity, with high-density multi-electrode array (HD-MEAs) to simultaneously record the spontaneous activity of the retina. In this paper, we introduce this instrument, describe its technical characteristics, and present a proof-of-concept experiment that shows how RGC spiking activity of explanted mice retinas respond to mechanical micro-stimulations of their photoreceptor layer. The data suggest that, under specific conditions of indentation, the retina perceive the mechanical stimulation as modulation of the visual input, besides the longer time-scale of activation, and the increase in spiking activity is not only localized under the indentation probe, but it propagates across the retinal tissue.

Traumatic macular retinoschisis in infants and children

PURPOSE

To provide detailed description of pediatric traumatic retinoschisis.

METHODS

The medical records of children with either abusive head trauma and traumatic macular retinoschisis seen at a single center from 1993 to 2006 were reviewed retrospectively. Clinical details were extracted from the record and photographic documentation. Evaluation regarding abuse excluded ophthalmology findings to avoid circular reasoning.

RESULTS

Of 134 patients with suspected abusive head trauma, 31 had retinoschisis. Mean age was 9 months. Of the 31, 22 (71%) offered a history of injury, and 9 (29%) were found unresponsive without history of injury; 6 were reportedly shaken. All patients had seizures, vomiting, and/or altered responsiveness. All had subdural hemorrhage, with cerebral edema in 17 (55%). In 10 (32%), there were findings of blunt force head injuries; in 4 of these there was no impact history. Retinal hemorrhages were present in all cases. Agreement between sidedness of retinoschisis and subdural hemorrhage was poor. Eleven patients had retinal folds, 3 of which had a hemorrhagic edge to the schisis. Nine patients had extracranial manifestations of abuse. Multidisciplinary team adjudications were as follows: of the 31 cases, 18 were suspicious for abuse, 11 were indeterminate, and 2 were possibly accounted for by accidental severe crush injury. Three children died, and 11 suffered neurological sequelae.

CONCLUSIONS

Traumatic retinoschisis in children is highly associated with subdural hemorrhage, neurologic symptoms, and poor outcomes. Even with a conservative approach to opinion formulation, traumatic retinoschisis was associated with likely abuse.

PATHOLOGY OF PERIMACULAR FOLDS DUE TO VITREORETINAL TRACTION IN ABUSIVE HEAD TRAUMA

PURPOSE

To demonstrate vitreoretinal traction as a mechanism for perimacular folds in abusive head trauma.

METHODS

We performed gross and histopathologic examination of eyes of children with suspected abusive head trauma and identified those with typical perimacular folds. Information was collected regarding the incident that led to the child's death and systemic manifestations noted at autopsy. Eyes were prepared in a fashion that allowed for demonstration of the vitreoretinal interface.

RESULTS

Ten eyes of five patients (2-13 months) were examined. All patients had systemic manifestations of abusive trauma including intracranial injury. All cases provided evidence of vitreoretinal traction producing perimacular folds. Condensed vitreous was seen attached to the apices of the retinal folds, and the detached internal limiting membrane comprising the inner surfaces of the schisis cavity. Four cases showed severe bilateral multilayered symmetric retinal hemorrhages extending to the ora serrata. All cases showed optic nerve sheath subdural hemorrhage and subarachnoid hemorrhage. Orbital hemorrhage was unilateral in two cases and bilateral in three cases. Four cases showed orbital fat hemorrhage. One case showed extraocular muscle sheath and cranial nerve sheath hemorrhage. Two cases showed juxtapapillary intrascleral hemorrhage.

CONCLUSION

Vitreoretinal traction is the likely mechanism of perimacular folds in abusive head trauma.

Hierarchical multiscale structure-property relationships of the red-bellied woodpecker (Melanerpes carolinus) beak

We experimentally studied beaks of the red-bellied woodpecker to elucidate the hierarchical multiscale structure-property relationships. At the macroscale, the beak comprises three structural layers: an outer rhamphotheca layer (keratin sheath), a middle foam layer and an inner bony layer. The area fraction of each layer changes along the length of the beak giving rise to a varying constitutive behaviour similar to functionally graded materials. At the microscale, the rhamphotheca comprises keratin scales that are placed in an overlapping pattern; the middle foam layer has a porous structure; and the bony layer has a big centre cavity. At the nanoscale, a wavy gap between the keratin scales similar to a suture line was evidenced in the rhamphotheca; the middle foam layer joins two dissimilar materials; and mineralized collagen fibres were revealed in the inner bony layer. The nano- and micro-indentation tests revealed that the hardness (associated with the strength, modulus and stiffness) of the rhamphotheca layer (approx. 470 MPa for nano and approx. 320 MPa for micro) was two to three times less than that of the bony layer (approx. 1200 MPa for nano and approx. 630 MPa for micro). When compared to other birds (chicken, finch and toucan), the woodpecker's beak has more elongated keratin scales that can slide over each other thus admitting dissipation via shearing; has much less porosity in the bony layer thus strengthening the beak and focusing the stress wave; and has a wavy suture that admits local shearing at the nanoscale. The analysis of the woodpeckers' beaks provides some understanding of biological structural materials' mechanisms for energy absorption.

Ocular complications of bungee jumping

AIM

In this paper, we will try to highlight the importance of various investigations and their crucial role in identifying whether the defect is structural or functional.

CASE HISTORY

A 24-year-old woman presented with ocular complications after bungee jumping. Subsequently, although all ophthalmic signs resolved, she complained of decreased vision in her left eye.

CONCLUSION

Initial ophthalmic injury was detected by optical coherence tomography scan showing a neurosensory detachment of the fovea. This was not initially detected on slit-lamp examination or fluorescein angiography. On later examination, although the optical coherence tomography scan showed no structural damage, electrodiagnostic tests showed a functional defect at the fovea.

Effect of slosh mitigation on histologic markers of traumatic brain injury: laboratory investigation

OBJECT

Helmets successfully prevent most cranial fractures and skull traumas, but traumatic brain injury (TBI) and concussions continue to occur with frightening frequency despite the widespread use of helmets on the athletic field and battlefield. Protection against such injury is needed. The object of this study was to determine if slosh mitigation reduces neural degeneration, gliosis, and neuroinflammation.

METHODS

Two groups of 10 adult male Sprague-Dawley rats were subjected to impact-acceleration TBI. One group of animals was fitted with a collar inducing internal jugular vein (IJV) compression prior to injury, whereas the second group received no such collar prior to injury. All rats were killed 7 days postinjury, and the brains were fixed and embedded in paraffin. Tissue sections were processed and stained for markers of neural degeneration (Fluoro-Jade B), gliosis (glial fibrillary acidic protein), and neuroinflammation (ionized calcium binding adapter molecule 1).

RESULTS

Compared with the controls, animals that had undergone IJV compression had a 48.7%-59.1% reduction in degenerative neurons, a 36.8%-45.7% decrease in reactive astrocytes, and a 44.1%-65.3% reduction in microglial activation.

CONCLUSIONS

The authors concluded that IJV compression, a form of slosh mitigation, markedly reduces markers of neurological injury in a common model of TBI. Based on findings in this and other studies, slosh mitigation may have potential for preventing TBI in the clinical population.

Ultrastructure of the distal retina of the adult zebrafish, Danio rerio

The organization, morphological characteristics, and synaptic structure of photoreceptors in the adult zebrafish retina were studied using light and electron microscopy. Adult photoreceptors show a typical ordered tier arrangement with rods easily distinguished from cones based on outer segment (OS) morphology. Both rods and cones contain mitochondria within the inner segments (IS), including the large, electron-dense megamitochondria previously described (Kim et al.) Four major ultrastructural differences were observed between zebrafish rods and cones: (1) the membranes of cone lamellar disks showed a wider variety of relationships to the plasma membrane than those of rods, (2) cone pedicles typically had multiple synaptic ribbons, while rod spherules had 1-2 ribbons, (3) synaptic ribbons in rod spherules were ∼2 times longer than ribbons in cone pedicles, and (4) rod spherules had a more electron-dense cytoplasm than cone pedicles. Examination of photoreceptor terminals identified four synaptic relationships at cone pedicles: (1) invaginating contacts postsynaptic to cone ribbons forming dyad, triad, and quadrad synapses, (2) presumed gap junctions connecting adjacent postsynaptic processes invaginating into cone terminals, (3) basal junctions away from synaptic ribbons, and (4) gap junctions between adjacent photoreceptor terminals. More vitread and slightly farther removed from photoreceptor terminals, extracellular microtubule-like structures were identified in association with presumed horizontal cell processes in the OPL. These findings, the first to document the ultrastructure of the distal retina in adult zebrafish, indicate that zebrafish photoreceptors have many characteristics similar to other species, further supporting the use of zebrafish as a model for the vertebrate visual system.

The eye examination in the evaluation of child abuse

Retinal hemorrhage is an important indicator of possible abusive head trauma, but it is also found in a number of other conditions. Distinguishing the type, number, and pattern of retinal hemorrhages may be helpful in establishing a differential diagnosis. Identification of ocular abnormalities requires a full retinal examination by an ophthalmologist using indirect ophthalmoscopy through a pupil that has been pharmacologically dilated. At autopsy, removal of the eyes and orbital tissues may also reveal abnormalities not discovered before death. In previously well young children who experience unexpected apparent life-threatening events with no obvious cause, children with head trauma that results in significant intracranial hemorrhage and brain injury, victims of abusive head trauma, and children with unexplained death, premortem clinical eye examination and postmortem examination of the eyes and orbits may be helpful in detecting abnormalities that can help establish the underlying etiology.

Hand-held spectral domain optical coherence tomography finding in shaken-baby syndrome

PURPOSE

The purpose of this study was to document the hand-held spectral domain optical coherence tomography (HHSD-OCT, Bioptigen, Durham, NC) findings in shaken-baby syndrome (SBS). The nonaccidental trauma in SBS has been associated with retinal findings, including hemorrhages in all layers of the retina and retinoschisis.

METHODS

Three consecutive patients with presumed SBS underwent complete ocular examination, fundus photography with the RetCam (Clarity Medical Systems, Pleasanton, CA), and imaging with the HHSD-OCT. Acquisition of the HHSD-OCT images required an assistant to stabilize the head of the infant.

RESULTS

All three patients had clinical findings consistent with SBS, including preretinal and intraretinal hemorrhages. Hand-held spectral domain optical coherence tomography documented focal posterior vitreous separation in four of the five eyes with multilayered retinoschisis in one eye, disruption of the foveal architecture and foveolar detachment in one eye, and disinsertion of the internal limiting membrane or inner retinoschisis in one eye. Hand-held spectral domain optical coherence tomography documented preretinal hemorrhages in all five eyes.

CONCLUSION

Hand-held spectral domain optical coherence tomography is helpful in the evaluation of patients with SBS. All patients in our series had vitreoretinal abnormalities not detected on clinical examination, including, for example, multilayered retinoschisis. Hand-held spectral domain optical coherence tomography allows high-resolution imaging of the vitreoretinal interface and retina in infants with SBS and has provided insight into the mechanism of various retinal findings.

Pathology of retinal hemorrhage in abusive head trauma

Abusive head injury, characterized by repeated acceleration-deceleration forces, is associated with retinal hemorrhages as demonstrated in many clinical and postmortem studies. The theory that vitreoretinal traction is the major factor in the pathogenesis of retinal hemorrhages is presently the most widely accepted explanation based on different lines of research. Postmortem examination of the eye and orbital structures is essential for recognizing abusive head injury and also for identifying other possible medical conditions which can cause retinal hemorrhage.

Retinal hemorrhages: advances in understanding

Retinal hemorrhage is a cardinal manifestation of abusive head injury characterized by repetitive acceleration-deceleration with or without blunt head impact. Detailed description of the hemorrhages and documentation are critical to diagnosis. Vitreoretinal traction appears to be the major causative factor. Outcome is largely dependent on brain and optic nerve injury.

Ischemic retinopathy and neovascular proliferation secondary to shaken baby syndrome

BACKGROUND

Ocular lesions known to occur after shaken baby syndrome (SBS) are epiretinal, intraretinal, and subretinal hemorrhages, which are present in up to 100% of patients. Retinoschisis and retinal folds have also been described. We describe three patients with SBS who presented with tractional retinal detachments secondary to neovascular proliferation and discuss the role of ischemia at the retinal level.

PATIENTS

Three patients (two 4-month-old babies and one 4-year-old child) with a history of SBS in the first year of life presented with tractional retinal detachment due to severe preretinal fibrovascular proliferation. Peripheral retinal ischemia and vascular disorganization were noted during clinical examination.

CONCLUSION

Although physiopathology of SBS remains disputed, ischemia has been accepted as the main feature of cerebral lesions. Ischemia could also be present at the retinal level as suggested by our patients' presentation. It could be induced by direct vitreous shearing of the capillary network or more probably by vascular leak due to brain edema and hypoxic damage of capillaries. Long-term ocular follow-up is necessary in SBS to treat these patients preventively.

Natural animal shaking: a model for non-accidental head injury in children?

BACKGROUND

Non-accidental head injury (NAHI) is a form of child abuse where a perpetrator may violently subject an infant to repeated acceleration-deceleration forces with or without head impact, producing injuries including retinal haemorrhages in most cases. Animal models have included laboratory shaking of mice and rats, but only a small fraction develop retinal haemorrhages presumably due to the small eyes, which would require unattainable force levels to mimic that sustained by the infant eye. Animal models are also problematic due to ethical issues raised by subjecting even anaesthetized animals to abusive injury.

METHODS

We investigated a naturally occurring event, where three animal victims were shaken by a canine. The eyes were harvested and examined histologically.

RESULTS

The victims' eyes showed no haemorrhage or retinoschisis.

CONCLUSIONS

Our model may not be a complete NAHI mimic. The discrepancies may ensue from anatomical and mechanical differences in the injury mechanism. Other models must be sought to further study this form of abusive eye injury.

Update on shaken baby syndrome: ophthalmology

PURPOSE OF REVIEW

Shaken baby syndrome is a common problem with a high morbidity and mortality. Ophthalmologists help manage this condition and therefore must keep abreast of current advances.

RECENT FINDINGS

Clinical updates include the discovery that retinal folds and traumatic retinoschisis can very rarely occur after crush head injury, but remain specific for shaken baby syndrome in other scenarios. Pathology updates include new studies on orbital histology and woodpecker anatomy that suggest the retinal and optic nerve hemorrhages in shaken baby syndrome are caused by shaking itself rather than secondary to intracranial pathology. Regarding this shaking injury, some primary prevention strategies have proven surprisingly effective. In the near future, serum biomarkers may be used as a screening tool for inflicted neurotrauma. Animal models such as the neonatal pig and computer models using finite element analysis are promising experimental techniques for studying shaken baby syndrome. Finally, child abuse recently became an accredited subspecialty of pediatrics, which will lead to further advances in patient care, education, research and prevention.

SUMMARY

Ophthalmologists play a key role in the diagnosis of shaken baby syndrome. In addition, they are in a unique position to study ophthalmic aspects of the syndrome, which in turn furthers the overall understanding of this devastating condition.