Disorder of Olfactory and Optic Nerve | Dr Anutosh Chakraborty

Olfactory and Optic Nerve

The olfactory and the optic nerve both have cranial nerves. The olfactory nerve is the first cranial nerve and the optic nerve is the second cranial nerve...

Olfactory nerve
The nerve arises from olfactory receptors in the nasal mucosa and passes through the cribriform plate of the anterior cranial fossa and terminates in the olfactory area in the frontal lobe.

  • Head injuries
  • Tumors of frontal lobe

Anosmia: Loss of sense of smell is usually caused by tumors of frontal lobe or head injuries causing damage to cribriform plate; also due to meningitis, hydrocephalus and in cases of hysteria.

Optic nerve
The optic nerve starts at the optic disk, which is located behind the eye. An optic disk is formed from the junction of strands of ganglion cell output (called axons) as it emerges from the eye. When the sensor comes out of the back of the eye, it passes through the remaining part of the posterior orbit (the socket of the eye) and the bony optic canal to emerge unconsciously from the lower front of the brain. At this point, the optic nerve from each eye connects and forms an X-shaped structure called the optic chiasm. Here, about two-thirds of the nerve fibers in each eye extend to one side of the brain, and the remaining nerve fibers fall into the chiasm to connect the fibers from one eye to the other side of the brain. This arrangement is important in producing binocular vision. After optic chiasm, nerve fibers travel through the optic nerve to various parts of the brain — mainly the lateral geniculate nuclei. Fibers from the lateral geniculate nuclei form optic radiation to the visual cortex, located in the occipital lobes behind the brain. Some nerve fibers leave the optic tract and do not enter the lateral geniculate nucleus, but instead enter the brain stem to provide information that ultimately determines pupil size.

Trauma, Vascular accidents, Tumors, Aneurysm, Basal meningitis

Papilledema: Edema of the optic disk or papilla from any cause; may be inflammatory (Papillitis) or due to passive venous congestion.

  • Increased intracranial pressure, tumors, abscess, meningitis, outflow block of 4th ventricle.
  • Optic neuritis
  • Diseases of retinal artery. Malignant hypertension
  • Obstruction to venous drainage
  • Chronic nephritis
  • Cerebral tumors
  • Pulmonary encephalopathy
  • In some cases of hematemesis and melena
  • Cerebral edema after head injury; cerebral anoxia
  • Vitamin A intoxication

On examination of disk [Optic nerve damage]
  • Congestion of retinal veins
  • Increased pinkness of the disk
  • Blurring of the disk margin starting on nasal side
  • Filling of physiological cup
  • Hemorrhage in and around the disk
  • Elevation of optic disk
  • Visual changes-Peripheral constriction and enlargement of 'Blind Spot'
  • Pallor of disk due to optic atrophy in later stages. Papillitis differs from papilledema in that it causes increased intracranial pressure and is often accompanied by a dramatic decrease in vision.

Retrobulbar neuritis / Optic neuritis: Inflammation of optic nerve which causes loss of vision.

  • Disseminated sclerosis
  • Vitamin deficiency, especially B12
  • Infections
  • Local-Retinitis
  • General-Syphilis, typhoid, smallpox
  • Toxins: Methyl alcohol and quinine and its derivatives, lead
  • Excessive smoking, contraceptive pill

  • Irritability: Pain in eye, worse by movement
  • Tenderness over eye
  • Papillitis: If the lesion is anteriorly
  • Severe loss of visual acuity
  • Loss is typically of central vision

Optic atrophy: Loss of fibers in the optic nerve is followed by reactive glioses and reduces  vascularization.

  • Primary
  • Secondary

  • Pressure on the nerve caused by glaucoma, tumor, aneurysms etc.
  • Optic neuritis due to any cause listed above
  • long-standing papilledema
  • Thrombosis of central retinal artery
  • Trauma
  • Genetically determined: Leber's optic atrophy
  • Diabetes mellitus
  • Poison: Alcohol. Quinine etc.

On examination: Pallor of disk

Optic nerve hypoplasia
Optic nerve hypoplasia (ONH) is a congenital malformed disease (hypoplasia) of the optic nerve. The optic nerve transmits information from the optic nerve into the retina of the eye and into the brain.

Differential diagnosis
Anterior ischemic optic neuropathy: Is a condition caused by interruption of blood supply to the optic nerve secondary to atherosclerotic or inflammatory disease of the ophthalmic artery or its branches.
It presents clinically as an acute, painless, visual loss in one eye, usually accompanied by an altitudinal visual field defect. In severe cases, visual field defect and visual loss in complete and permanent. The fundus shows a pale swollen optic disk surrounded by splinter shaped peripapillary hemorrhages.

Syndrome of bitemporal hemianopia: This type of visual disorder is usually related to suprasellar extension of a pituitary adenoma. but may also be due to a cranio-pharyngioma, macular aneurysm of the Circle of Wills; meningioma of the tuberculum sella and rarely sarcoidosis, metastatic carcinoma, and Hand-Schuller-Christian disease.

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