Comparative retinal ganglion cell and optic nerve morphology

The optic nerve is divided in four regions: intraocular, intraorbital, intracanalicular, and intracranial. The vertebrate retinal ganglion cells are classified by morphology, physiology and soma size. Species differences and similarities occur with retinal ganglion cells. Alpha retinal ganglion cells have large somata, large dendritic fields, large-diameter axons, and are most dense in the peripheral retina. Beta retinal ganglion cells have smaller diameter somata, smaller dendritic fields, small diameter axons, and predominate in the central retina. Gamma retinal ganglion cells are a heterogenous class of cells and have small diameter axons, and slow axon conduction velocities. The spatial distribution and organization of the retinal ganglion cells extends retinotopically through the nerve fiber layer, optic nerve, optic chiasm, optic tract, lateral geniculate nucleus, and visual cortex. The retinal nerve fiber layer thickness decreases from the optic disk toward the periphery of the retina. The retrobulbar optic nerve axon counts and axon density vary by species, with larger nerves having higher axon counts. Decussation of the optic nerve axons at the optic chiasm varies with 100% decussation in most birds and fish, 65% in cats, 75% in dogs, 80–90% in large animals, and 50% in primates. Centrifugal axons also occur in the optic nerve and may represent a method by which the brain can influence retinal activity.     

Optic nerve head neuroretinal rim blood flow differences in monkeys with laser-induced glaucoma

INTRODUCTION: The blood flow of the neuroretinal rim (NRR) of the optic nerve head (ONH) of the rhesus monkey with laser-induced glaucoma was examined. METHODS: Argon laser photocoagulation of the trabecular meshwork to induce elevated intraocular pressure (IOP) was performed in one eye of nine normal male rhesus monkeys. The nasal and temporal NRR of the monkey ONH were examined by the Heidelberg retina tomograph/flowmeter (HRT/HRF) under neuromuscular blockade. A mixed effect analysis of variance was used to determine significant differences between eyes and between locations in the eyes. RESULTS: The average IOP in the hypertensive glaucoma and normal eyes was 34.8 +/- 7.2 and 16.0 +/- 1.9 mmHg, respectively. The HRT determined average overall cup to disc (C/D) area ratio in the glaucoma and normal eyes, which was 0.49 +/- 0.28 and 0.22 +/- 0.16, respectively. The mean temporal NRR HRF flow in the hypertensive eyes was significantly greater than in the normotensive eyes (P < 0.0001), than in the nasal NRR of the hypertensive eyes (P < 0.0001) and than in the nasal NRR of the normotensive eyes (P < 0.01). The mean nasal NRR HRF flow in the hypertensive eyes was significantly less than in the nasal NRR of the normotensive eyes (P < 0.01). There was no statistical difference between the mean HRF flow of the temporal and nasal NRR of the normotensive eyes. The elevated IOP positively influenced the flow values in the hypertensive eye (r = 0.724). CONCLUSIONS: The capillary microcirculation of the temporal NRR of the rhesus monkey ONH with laser-induced glaucoma has significantly increased blood flow, and the nasal NRR significantly reduced blood flow compared to blood flow in the NRR of normal normotensive monkey eyes.     

Distinctive histopathologic features of canine optic nerve hypoplasia and aplasia: a retrospective review of 13 cases

Canine optic nerve hypoplasia (ONH) and aplasia (ONA) are significant neuro-ophthalmologic disorders that have been reported in several species. The purpose of this study was to describe the distinctive histopathologic features of ONH and ONA in canine patients identified from a collection of 20 000 ocular submissions at the comparative ocular pathology laboratory of Wisconsin from 1989 to 2006. The following information about ONH and ONA cases was collected: signalment, and clinical and gross findings, including unilateral vs. bilateral involvement. Microscopic evaluation was performed, with attention to optic nerve malformation, retinal ganglion cell (RGC) and nerve fiber layer (NFL) loss, and retinal disorganization. The distribution of retinal vasculature was recorded and a search for unusual findings of ONH and ONA was performed. Information and histologic documentation was available for 13 cases. Eight cases of ONH and five cases of ONA were identified. The average group age was 20.2 months and 16.1 months, respectively. The most common breed was the Shih Tzu (3/13). ONH usually presented bilaterally (7/8); all ONA cases presented as a unilateral disease (5/5). The morphologic findings in the optic nerve (ON) in ONH included variable degrees of ON hypoplasia and gliosis, as well as ectopic vestigial ON remnants within orbital nerves and connective tissues. The NFL was detected in the majority of the ONH cases; however, RGCs were rare or absent. Mild retinal disorganization was seen occasionally. Most cases of ONH were associated with regional peripheral retinal blood vessel extension into the vitreous, leaving the peripheral retina avascular. In ONA cases the retinal blood vessels, NFL and RGCs were totally absent and retinal disorganization was severe. Distinctive microscopic features encountered in ONA included anterior segment dysgenesis in some cases. The retina in these cases was stretched across the posterior lens capsule, never making contact with the posterior pole of the globe. The current study reviews the human and veterinary literature pertaining to ONH and ONA, compares ONH and ONA in dogs, and presents related ophthalmic histopathologic findings that have not been reported previously.     

Trauma: physiology, pathophysiology, and clinical implications

Objective: To review the physiology, pathophysiology, and consequences of trauma. The therapeutic implications of hypovolemia, hypotension, hypothermia, tissue blood flow, oxygen delivery, and pain will be discussed. Data Sources: Human and veterinary clinical and research studies. Human and veterinary data synthesis: Trauma is defined as tissue injury that occurs more or less suddenly as a result of violence or accident and is responsible for initiating hyothalamic–pituitary–adrenal axis, immunologic and metabolic responses that are designed to restore homeostasis. Tissue injury, hemorrhage, pain, and fear are key components of any traumatic event. Trauma and blood loss result in centrally integrated autonomic‐mediated cardiovascular responses that are designed to increase heart rate, systemic vascular resistance, and maintain arterial blood pressure (ABP) to vital organs at the expense of blood flow to the gut and skeletal muscle. Severe trauma elicits exuberant physiologic, immunologic, and metabolic changes predisposing the animal to organ malfunction, a systemic inflammatory response, infection, and multiple organ dysfunctions. The combination of both central and local influences produces regional redistribution of blood flow among and within tissue beds which, when combined with impaired vascular reactivity, leads to maldistribution of blood flow to tissues predisposing to tissue hypoperfusion and impaired oxygen delivery and extraction. Gut blood flow and viability may serve as a sentinel of patient survival. These consequences are magnified in animals suffering from pain or that become hypothermic. Successful treatment of traumatized animals goes beyond the restoration of blood pressure and urine output, is dependent on a fundamental understanding of the pathophysiologic processes responsible for the animals current physical status, and incorporates the reduction of pain, stress, and the systemic inflammatory response and methods that restore microcirculatory blood flow and tissue oxygenation. Conclusions: Severe trauma is a multifaceted event and is exacerbated by hypothermia, pain, and stress. Therapeutic approaches must go beyond the simple restoration of vascular volume and ABP by maintaining tissue blood flow, restoring tissue oxygenation, and preventing systemic inflammation.     

Expression of glial cells molecules in the optic nerve of adult dromedary camel (Camelus dromedarius): A histological and immunohistochemical analysis

The optic nerve (ON) is an important organ in the visual system of animals, which transfers electrical impulses towards the brain from the retina. High enrichment of glial cells in ON is known to support neuron and regulate retinal homoeostasis. However, research on immunohistochemical of glial cells proteins in the camel is scanty in available literature. Hence, the current work is an attempt to investigate the histomorphology of camel ON with regard to the expression patterns of glial fibrillary acidic protein (GFAP), myelin basic protein (MBP) and Iba1 for the three glial subtypes, namely astrocytes, oligodendrocytes and microglia, respectively. Optic nerves from fourteen dromedary camels were dissected and preserved in 10% formalin. Then, the paraffin‐embedding sections were subjected for histochemical and immunohistochemical analysis. Our results demonstrated that ON axons aggregate into fascicles that surrounded by light and densely stained glial cells. Then, we examined the myelin sheath using Heidenhain's and Mallory's phosphotungstic acid staining. Immunoassay results revealed that GFAP is enriched in the ON and distributed evenly, whereas MBP and Iba1 were present at scanty levels. Further analysis of mRNA level of GFAP, MBP and Iba1 in the ON confirmed an elevation of GFAP expression compared to MBP and Iba1. We further found partial co‐localization of different types of glial cells that reflect their coordinated function in the ON. Although our data provide the first evidence for differential expression pattern of glial proteins, further molecular studies still required to reveal the specific function of these molecules in the camel ON.