Optic Nerve
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Questions and Answers

Which part of the brain is the optic nerve primarily composed of?

  • Gray matter
  • White matter (correct)
  • Retinal ganglion cells
  • Cranial nerves

    • Where do the axons of retinal ganglion cells exit the eye to form the optic nerve?

  • Retinal ganglion cell layer
  • Retinal nerve fiber layer
  • Optic nerve head (correct)
  • Lateral geniculate nucleus

    • Where do the majority of canine retinal ganglion cell axons ultimately project to?

  • Optic chiasm
  • Superior colliculus
  • Lateral geniculate nucleus (correct)
  • Hypothalamus

    • Which type of collagen is primarily found in the extracellular matrix (ECM) of the dog LC?

    <p>Collagen type I</p> Signup and view all the answers

    What is the approximate thickness of the canine central laminar?

    <p>~500 μm</p> Signup and view all the answers

    Which of the following does NOT play a significant role in susceptibility to axonal damage in glaucoma?

    <p>Regional differences in pore size</p> Signup and view all the answers

    What is the role of the laminar insertion zone in the dog LC?

    <p>Supporting the ONH structures</p> Signup and view all the answers

    Which part of the optic nerve can be visualized on ophthalmoscopy?

    <p>The anterior-most part, the optic disc or optic papilla</p> Signup and view all the answers

    Which region of the optic nerve is the longest?

    <p>The retrobulbar, orbital segment</p> Signup and view all the answers

    Where do axons from the nasal retina of carnivores cross at the optic chiasm?

    <p>To the contralateral LGN and visual cortex</p> Signup and view all the answers

    Why does the optic nerve represent an extremely vulnerable segment of the visual pathway?

    <p>Due to limited functional redundancy</p> Signup and view all the answers

    Which artery supplies the primary blood flow to the eye in dogs?

    <p>External ophthalmic artery</p> Signup and view all the answers

    What is the main determinant of the translaminar pressure gradient (TLPG)?

    <p>Intraocular pressure (IOP)</p> Signup and view all the answers

    Which region of the optic nerve is more likely to be directly impacted by IOP?

    <p>Superficial and laminar layers</p> Signup and view all the answers

    What is the role of the short posterior ciliary arteries in the canine optic nerve?

    <p>Supply the LC, choroid, retina, and ONH</p> Signup and view all the answers

    Which species has a larger mean fiber diameter of individual axons in the intraorbital optic nerve compared to humans and monkeys?

    <p>Dogs</p> Signup and view all the answers

    What is the diameter of the canine intraorbital optic nerve?

    <p>1825.8 ± 59.7 μm</p> Signup and view all the answers

    What is the approximate increase in diameter of the canine optic nerve as it exits the globe?

    <p>1.4-fold</p> Signup and view all the answers

    Which cell type is responsible for myelination of optic nerve axons in mammals?

    <p>Oligodendrocyte</p> Signup and view all the answers

    What is the role of myelin in optic nerve axons?

    <p>Reduce neuronal energy and metabolic demands</p> Signup and view all the answers

    Which region of the optic nerve is myelinated in mammals?

    <p>Posterior to the lamina cribrosa</p> Signup and view all the answers

    What is the primary cell type responsible for myelination of cranial nerves (except the olfactory nerve) in mammals?

    <p>Schwann cell</p> Signup and view all the answers

    Which technique is NOT generally used in veterinary patients to evaluate the optic disc?

    <p>Binocular indirect ophthalmoscopy with a headset</p> Signup and view all the answers

    What is the primary color of the stimuli used in chromatic pupillometry?

    <p>Red</p> Signup and view all the answers

    Which type of retinal ganglion cells are responsible for generating sustained pupillary light reflex (PLR) responses to blue stimuli?

    <p>Intrinsically photoreceptive retinal ganglion cells</p> Signup and view all the answers

    What can pupillometry be useful for in determining the most appropriate diagnostic tests for acute onset blindness?

    <p>Differentiating between optic nerve diseases</p> Signup and view all the answers

    Which of the following animals has the highest percentage of optic nerve axons crossing the midline at the optic chiasm?

    <p>Bird</p> Signup and view all the answers

    Which of the following is NOT a location intimately associated with the optic chiasm in dogs?

    <p>Third ventricle</p> Signup and view all the answers

    Which of the following reflexes is NOT used to assess vision in dogs during a neuro-ophthalmic examination?

    <p>Dazzle reflex</p> Signup and view all the answers

    Which of the following statements about the pupillary light reflex (PLR) is NOT true?

    <p>It is primarily initiated by photoreceptor activity</p> Signup and view all the answers

    Which ophthalmoscopy lens is considered a reasonable compromise for evaluation of the optic nerve head (ONH) in canine patients?

    <p>14D indirect ophthalmoscopy lens</p> Signup and view all the answers

    What are the predicted lateral and axial magnifications when using a 14D indirect ophthalmoscopy lens for evaluation of the ONH in canine patients?

    <p>Lateral magnification: 2.6x, axial magnification: 9.03x</p> Signup and view all the answers

    What feature of the ONH is easier to visualize in dogs?

    <p>Physiologic pit</p> Signup and view all the answers

    What is the normal average cup to disc ratio for humans?

    <p>0.32</p> Signup and view all the answers

    Which imaging technique is currently considered unreliable for measuring neuroretinal rim width and optic cup width and depth in dogs with glaucoma?

    <p>Heidelberg Retinal Tomograph cLSO system</p> Signup and view all the answers

    Which imaging technique relies on comparison with a normal database, which is lacking for dogs?

    <p>Heidelberg Retinal Tomograph cLSO system</p> Signup and view all the answers

    Which imaging technique is insensitive to the early phases of tissue loss in the neuroretinal rim in optic nerve degeneration and glaucomatous atrophy?

    <p>Fluorescein angiography</p> Signup and view all the answers

    Which imaging technique provides exquisitely detailed images of integrity, course and perfusion defects in the microvasculature of the human optic nerve without need for intravenous injection of fluorescent dyes?

    <p>OCT angiography</p> Signup and view all the answers

    Which imaging technique is considered the cross-sectional imaging technique of choice in diagnostic investigation of humans with suspected prechiasmatic optic nerve disease?

    <p>Magnetic Resonance Imaging (MRI)</p> Signup and view all the answers

    What can Magnetic Resonance Imaging (MRI) be used to identify or exclude in the differential diagnosis of canine optic nerve swelling?

    <p>Intraorbital or intracranial mass lesions</p> Signup and view all the answers

    What did MRI findings in dogs with optic neuritis include?

    <p>Hyperintensity of one or both optic nerves</p> Signup and view all the answers

    Which breed of dog has published reports of achiasmatic optic nerves with nystagmus?

    <p>Belgian Sheepdog (Groenendael)</p> Signup and view all the answers

    What is the most striking clinical feature observed in dogs with achiasmatic optic nerves?

    <p>Congenital nystagmus</p> Signup and view all the answers

    Which breed of dog has been reported to have bilateral optic nerve aplasia?

    <p>Irish Wolfhound</p> Signup and view all the answers

    Which imaging technique is considered superior to computed tomography for visualizing the optic nerves in dogs?

    <p>Magnetic Resonance Imaging (MRI)</p> Signup and view all the answers

    What is the approximate diameter of the optic nerve sheath complex in dogs?

    <p>3.7 mm</p> Signup and view all the answers

    What is the primary cause of enlargement of the optic nerve sheath in patients with increased intracranial pressure?

    <p>Shift in cerebrospinal fluid (CSF)</p> Signup and view all the answers

    What imaging technique can provide noninvasive assessment of white matter tracts, including the optic nerves, in both humans and animals?

    <p>Diffusion Tensor Imaging (DTI)</p> Signup and view all the answers

    Which imaging technique is considered technically demanding and requires sedation or general anesthesia in veterinary patients?

    <p>Pattern visual evoked potential</p> Signup and view all the answers

    What is the term used to describe a small optic disc in an eye with clinically normal pupillary light reflexes (PLRs) and vision?

    <p>Micropapilla</p> Signup and view all the answers

    What is the range of optic nerve head (ONH) size considered statistically abnormally small in dogs?

    <p>Less than 1.7 mm in diameter</p> Signup and view all the answers

    What is the primary reason that visual evoked potential (VEP) recording is not commonly performed in clinical veterinary practice?

    <p>Need for consistent sedation or anesthesia</p> Signup and view all the answers

    Which imaging technique provides detailed information complementary to MRI in the evaluation of patients with orbital trauma, including detection and localization of metallic foreign bodies and bone fragments?

    <p>Computed tomography (CT)</p> Signup and view all the answers

    Which imaging technique has the advantage of seldom requiring general anesthesia in veterinary patients and has been widely used in human patients as a surrogate measure of intracranial pressure (ICP)?

    <p>Ultrasonography</p> Signup and view all the answers

    Which electrophysiological test is the most widely utilized in the diagnosis of human optic nerve disease and is used to evaluate optic nerve function?

    <p>Visual-evoked potential (VEP)</p> Signup and view all the answers

    Which imaging technique is costly and time consuming for longitudinal monitoring of patients and would require general anesthesia for immobilization in dogs?

    <p>Magnetic resonance imaging (MRI)</p> Signup and view all the answers

    Which of the following is true about optic nerve hypoplasia in dogs?

    <p>Unilateral optic nerve hypoplasia can result in total blindness.</p> Signup and view all the answers

    Which of the following is a possible cause of reduced numbers of optic nerve axons in patients with optic nerve hypoplasia?

    <p>All of the above.</p> Signup and view all the answers

    Which of the following breeds is NOT mentioned as having a reported occurrence of optic nerve hypoplasia or micropapilla?

    <p>Golden Retrievers</p> Signup and view all the answers

    What is the primary cell type responsible for myelination of optic nerve axons in mammals?

    <p>Glial cells</p> Signup and view all the answers

    Which breed is NOT mentioned as having a reported occurrence of optic nerve coloboma?

    <p>German Shepherds</p> Signup and view all the answers

    Which ocular defect is NOT mentioned as being associated with optic nerve coloboma?

    <p>Optic neuritis</p> Signup and view all the answers

    Which breed is mentioned as having sporadic occurrences of optic nerve coloboma?

    <p>Basenji</p> Signup and view all the answers

    Which breed of dog is NOT mentioned as having a reported occurrence of optic nerve coloboma?

    <p>Poodles</p> Signup and view all the answers

    What is the risk factor associated with large colobomas of the optic nerve head in dogs?

    <p>Retinal tears and detachment</p> Signup and view all the answers

    What is the suggested cause of colobomas in dogs with Collie Eye Anomaly?

    <p>Genetic modifier</p> Signup and view all the answers

    What imaging technique is considered unreliable for measuring neuroretinal rim width and optic cup width and depth in dogs with glaucoma?

    <p>Optical coherence tomography (OCT)</p> Signup and view all the answers

    Which of the following is a characteristic feature of glaucomatous optic neuropathy in dogs?

    <p>Optic disc cupping</p> Signup and view all the answers

    What is the most likely cause of vision loss with a relatively normal fundus appearance in dogs?

    <p>SARDS</p> Signup and view all the answers

    Which of the following is NOT a potential cause of acquired optic nerve disorders in dogs?

    <p>Myelination of optic nerve axons</p> Signup and view all the answers

    Which of the following is a reported cause of optic neuritis in dogs?

    <p>All of the above</p> Signup and view all the answers

    In a retrospective study of 96 cases of canine optic neuritis, what percentage of patients had an etiologic diagnosis established?

    <p>80%</p> Signup and view all the answers

    Which of the following breeds is more likely to be diagnosed with MUO (meningoencephalomyelitis of unknown etiology)?

    <p>Small breed dogs</p> Signup and view all the answers

    What is the histologic diagnosis for both granulomatous meningoencephalitis (GME) and necrotizing encephalitis?

    <p>Histopathologic spectrum</p> Signup and view all the answers

    Which of the following is NOT a cause of optic disc swelling that can mimic pseudopapilledema in dogs and humans?

    <p>Inflammation</p> Signup and view all the answers

    What is the term used to describe the elevation of the optic nerve head (ONH) surface by prelaminar myelination of nerve fibers in clinically healthy, normal dogs?

    <p>Pseudopapilledema</p> Signup and view all the answers

    What is the imaging technique that is less likely to be informative in dogs with pseudopapilledema compared to humans?

    <p>Autofluorescence imaging</p> Signup and view all the answers

    What is the main factor that distinguishes pseudopapilledema from true papilledema in dogs?

    <p>Clinical signs of neurologic or systemic disease</p> Signup and view all the answers

    Which of the following is a characteristic feature of neoplastic infiltrates in the optic nerve and ONH?

    <p>Unilateral ONH edema</p> Signup and view all the answers

    Which of the following is a proposed pathogenesis of papilledema associated with raised intracranial pressure?

    <p>Compression of optic nerve fibers</p> Signup and view all the answers

    Which of the following is a reason why papilledema in dogs may go unrecognized in many cases?

    <p>All of the above</p> Signup and view all the answers

    Which of the following is a target organ damage secondary to systemic arterial hypertension in humans?

    <p>Optic nerve atrophy</p> Signup and view all the answers

    Which of the following is NOT listed as a cause of optic neuritis in dogs?

    <p>Trauma to the optic nerve</p> Signup and view all the answers

    Which of the following is NOT mentioned as a clinical sign of optic neuritis in dogs?

    <p>Bilateral optic nerve swelling</p> Signup and view all the answers

    Which of the following is NOT mentioned as a funduscopic abnormality associated with optic neuritis in dogs?

    <p>Swollen and edematous optic nerve head</p> Signup and view all the answers

    Which of the following imaging techniques is considered superior to computed tomography for visualizing the optic nerves in dogs?

    <p>Magnetic resonance imaging (MRI)</p> Signup and view all the answers

    Which imaging technique is recommended to establish an etiologic diagnosis of canine optic nerve disease whenever possible?

    <p>MRI</p> Signup and view all the answers

    Which imaging technique has higher sensitivity in detecting MUO in dogs?

    <p>MRI with T2-weighted sequences</p> Signup and view all the answers

    Which diagnostic testing has greater sensitivity and specificity for infectious diseases in dogs with inflammatory CSF findings?

    <p>CSF analysis</p> Signup and view all the answers

    Which of the following is the most common primary tumor involving the canine optic nerve?

    <p>Optic nerve meningioma</p> Signup and view all the answers

    What is the approximate percentage of ocular neoplasms submitted to a busy mail-in ocular pathology service that are accounted for by canine orbital meningioma?

    <p>1%</p> Signup and view all the answers

    Which of the following is a characteristic feature of primary canine orbital meningiomas on advanced imaging?

    <p>Foci of osseous and chondroid metaplasia</p> Signup and view all the answers

    Which of the following is a characteristic feature of optic nerve gliomas in dogs?

    <p>Formation of whorls of spindle cells</p> Signup and view all the answers

    Which of the following is a potential contributor to loss of retinal ganglion cell (RGC) axons in glaucomatous optic neuropathy?

    <p>Compression of optic nerve capillaries</p> Signup and view all the answers

    What is the primary cause of optic nerve damage in dogs with glaucoma?

    <p>Compression of optic nerve capillaries</p> Signup and view all the answers

    Which of the following is a potential consequence of decreased vascular perfusion in the optic nerve?

    <p>Axonal degeneration</p> Signup and view all the answers

    What is the role of hypoxia and ischemia in acute glaucoma in dogs?

    <p>Contributors to axonal degeneration</p> Signup and view all the answers

    Which of the following is a potential treatment option for patients with confirmed MUO or isolated optic neuritis?

    <p>Immunosuppressive doses of corticosteroids</p> Signup and view all the answers

    What is the recommended dosage of corticosteroids for systemic corticosteroid therapy in patients with no other evidence of systemic infectious disease?

    <p>0.25-0.5 mg/kg/day</p> Signup and view all the answers

    Which of the following is NOT a second-line immunosuppressive and immunomodulatory regimen proposed for the management of MUO?

    <p>Adjunctive procarbazine</p> Signup and view all the answers

    What is the prognosis for long-term recovery and retention of vision in cases of optic neuritis?

    <p>Guarded to poor</p> Signup and view all the answers

    Which type of glioma is predominantly found in the canine optic nerve?

    <p>Astrocytomas</p> Signup and view all the answers

    What are the common intraocular complications of optic nerve gliomas in dogs?

    <p>Retinal detachment, pre-iridal fibrovascular membranes, intraocular hemorrhage, and secondary glaucoma</p> Signup and view all the answers

    Which breed has a strong predilection for canine ocular gliovascular syndrome (COGS)?

    <p>Labrador Retriever</p> Signup and view all the answers

    What is the primary imaging technique used to suggest an ONH mass when ophthalmoscopy is not possible in dogs?

    <p>Ocular ultrasonography</p> Signup and view all the answers

    Which of the following is a potential complication of traumatic globe proptosis in dogs?

    <p>Optic nerve avulsion</p> Signup and view all the answers

    What is a potential cause of traumatic optic neuropathy in dogs?

    <p>Penetrating foreign bodies</p> Signup and view all the answers

    What treatment option is typically used for traumatic optic neuropathy in dogs?

    <p>High-dose corticosteroid therapy</p> Signup and view all the answers

    What is a potential cause of optic nerve degeneration in dogs?

    <p>Optic nerve compression</p> Signup and view all the answers

    Which imaging technology may aid in the interrogation of alterations in ONH blood supply in glaucoma patients?

    <p>OCT angiography</p> Signup and view all the answers

    Which mechanism is NOT believed to play a contributory role in glaucomatous optic neuropathy and subsequent blindness in dogs with glaucoma?

    <p>Vascular occlusion</p> Signup and view all the answers

    What is the likelihood of a single neuroprotective therapy being highly effective in preserving vision in glaucoma patients?

    <p>Unlikely</p> Signup and view all the answers

    Which of the following is a clinical hallmark of glaucomatous optic neuropathy in both humans and dogs?

    <p>Progressive excavation of the prelaminar tissues</p> Signup and view all the answers

    Which of the following is a factor that can influence the susceptibility of ONH structures and resident cells to damage associated with fluctuations in IOP?

    <p>Differences in ECM character and turnover within the ONH</p> Signup and view all the answers

    Which of the following is a characteristic feature of glaucomatous optic neuropathy in dogs?

    <p>Progressive posterior displacement of the surface of the ONH</p> Signup and view all the answers

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