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OPTIC NERVE DISEASES

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Optic Disc Pits and Associated Serous Macular Detachments  
 

Congenital pit of the optic disc appears as a localized oval or round depression within the nerve head.

Approximately 40%...

Congenital pit of the optic disc appears as a localized oval or round depression within the nerve head.

Approximately 40% of eyes with congenital optic pit have an associated serous retinal detachment at one time or another, frequently involving the macular region. Chronic retinal detachment can result in lamellar macular holes, cystic retinal degeneration, or retinal pigment epithelial atrophy.

Optical coherence tomography generally reveals a bi-laminar structure, with schisis-like retinal changes overlying a central neurosensory retinal detachment, usually confined to the posterior pole and contiguous with the optic disc.

The origin of the subregional fluid is uncertain: there is speculation that it may arise from the cerebrospinal fluid, the liquefied vitreous, the choroid or the orbit, made easier by vitreous tractions.

In our studies, vitrectomy seems essential in removing these vitreous tractions and we conclude that the anatomical repair may be easier if communication between the pit and the retinal layers is sealed.

Early hypo-fluorescence is seen in the optic pit due to an absence of vessels. Late staining of the tissue in the optic pit is seen.

References

Brown GC, Tasman WS: Congenital Anomalies of the Optic Disc. New York, Grune and Stratton, 1983, pp 95-191.

Travassos A, Travassos AT: Optic Pit: Revisão de Casos Cirúrgicos e Abordagem Terapêutica Inovadora. Revista da Sociedade Portuguesa de Oftalmologia – 2012, Vol35: pp 273-282.

Optic Disc Drusen  
 

Optic disc drusen are calcified hyaline bodies deposited in the pre-laminar optic nerve. The formation of drusen is related to...

Optic disc drusen are calcified hyaline bodies deposited in the pre-laminar optic nerve. The formation of drusen is related to axonal degeneration of the optic nerve head. Most are congenital, bilateral, and may become visible from the 1st or 2nd decade of life.

The clinical picture may be characterized by decreased visual acuity and visual field defects. More rarely, drusen can lead to vascular occlusive changes and/or bleeding of the optic disc and retina.

Drusen can be easily identified when they appear as bright yellow hyaline bodies in ophthalmoscopy. When they are inside the nervous tissue of the optic nerve head, they may give a false appearance of optic disc edema (pseudo-papilledema). Superficial drusen are also identified by fluorescein angiography, showing autofluorescence before injection and exhibiting nodular hyperfluorescence after injection. On ultrasonography optic nerve head drusen appear as hyperechogenic with posterior shadowing.

Anterior Ischemic Optic Neuropathy  
 

Anterior ischemic optic neuropathy is an ischemic damage of the optic nerve head. It is characterized by a painless unilateral...

Anterior ischemic optic neuropathy is an ischemic damage of the optic nerve head. It is characterized by a painless unilateral visual loss, developing over a period of hours to days. Relative afferent pupillary defect is usually present, unless there is bilateral optic neuropathy. A visual field defect is usually found, most commonly altitudinal or arcuate.

An important distinction must be made between two clinical pictures that have different therapeutic and prognostic implication: arteritic anterior ischemic optic neuropathy (AAION) and non-arteritic anterior ischemic optic neuropathy (NAION).

AAION is the less frequent of the two entities, corresponding to 5-10% of the cases of AION. It is a serious condition corresponding to the occlusion of the short posterior cilliary arteries by an inflammatory process. The mean age of diagnosis is 70 years, or 10 years more than NAION.

A good clinical history is fundamental in this group of patients. NAION is frequently accompanied by malaise, anorexia and weight loss, fever, joint and muscle pain. Headache and scalp tenderness in the temporal artery territory may be present. The most specific symptom is jaw claudication. A commonly associated syndrome is that of polymyalgia rheumatic.

Visual acuity is usually severely compromised, being < 20/200 in 60% of patients. Fundus examination usually reveals a pale optic disc edema. Cotton wool spots may be present. Choroidal ischemia is frequent and manifests as peripapillary pallor and edema and delayed choroidal perfusion in fluorescein angiography. Erythrocyte sedimentation rate, C-reactive protein, leukocyte count and alkaline phosphatase levels are usually elevated, while erythrocyte count and hemoglobin levels are usually depressed. Diagnosis is confirmed with temporal artery biopsy, showing inflammatory destruction of media-intima junction, with or without giant cells. A positive biopsy is diagnostic; however a negative one does not exclude the diagnosis.

Once there is a high clinical suspicion, treatment should be initiated promptly with a high dose corticosteroid. Prompt treatment is intended not to improve the vision of the affected eye, but to avoid systemic vascular complications as well as to preserve the fellow eye (involved in up to 95% of patients in the following days to weeks if untreated).

NAION is more common, corresponding to 90-95% of the cases of AION. The mean age of diagnosis is 60 years. Visual loss is usually less severe than that of AAION with >60% of patients having visual acuities greater than 20/200. Patients usually report visual loss noted on awakening.

Fundus examination reveals an optic disc edema, diffuse or sectorial, pale or hyperemic. The observation of the fellow eye usually reveals a small optic disc, with a small or absent physiologic cup. Usually the optic disk becomes atrophic after 4-8 weeks. Fluorescein angiography demonstrates a delayed optic disc filling in 75% of the cases. Crowding of the optic disc, hypertension, diabetes, smoking and hyperlipidemia are demonstrated risk factors for NAION.

There is no proven treatment for NAION or for prophylaxis of the fellow eye.

Myelinated Fibers  
 

Myelinated retinal nerve fibers are a congenital condition characterized by the presence of myelin fibers that extend on to the...

Myelinated retinal nerve fibers are a congenital condition characterized by the presence of myelin fibers that extend on to the retina adjacent to the optic nerve. On fundus examination they appear as bright white flame-shaped streaks, usually contiguous with the margin of the optic disc. The cause remains unknown.

Three different types of myelination have been described:

  • Type 1 - along the superior temporal arcade
  • Type 2 - along both the arcades
  • Type 3 - with no contiguity with the disc

This condition is nonprogressive and it does not disappear or regress. It does not usually interfere with vision and it is observed as an isolated finding. However, various degrees of decreased vision and scotoma may occur when extensive myelination involves the retina.

Toxic Optic Neuropathy  
 

Toxic optic Neuropathy is an optic nerve lesion resulting from exposure to systemic medications or environmental toxins.

The clinical picture...

Toxic optic Neuropathy is an optic nerve lesion resulting from exposure to systemic medications or environmental toxins.

The clinical picture is characterized by a progressive, insidious and painless bilateral loss of central vision.

Initially, ophthalmic examination may be characterized by a paucity of clinical signs. There may be a mild depression of central retinal sensitivity, progressing to a more severe difuse visual loss with decreased visual acuity, dyschromatopsia, and central or cecocentral scotoma. If the offending agent is not identified and suspended, optic atrophy eventually ensues.

The most common pharmacological offending agents are: ethambutol, isoniazid, chloramphenicol, penicillamine, cysplatin and vincristine. Environmental toxins include: methanol, ethylene glycol and heavy metals.

The most common syndrome of toxic damage to the optic nerve is that of tobacco-alcohol amblyopia. It is postulated that trace amounts of cyanide in tobacco smoke are responsible for the nerve fiber damage. Ethanol abuse is probably associated with optic neuropathy, because of the associated malnutrition. In these patients suspension of the toxins, oral multivitamins and intramuscular injections of hydroxycobalamin can halt the progression and eventually reverse visual loss in initial stages.

Besides the toxicological habits a thorough nutritional history should be obtained and specific nutritional deficiencies should be sought and corrected.

Optic Nerve Hypoplasia  
 

Optic nerve hypoplasia (ONH) is a congenital condition in which the optic nerve is underdeveloped (small) and is characterized by...

Optic nerve hypoplasia (ONH) is a congenital condition in which the optic nerve is underdeveloped (small) and is characterized by a decreased number of optic nerve axons. It can present unilaterally or bilaterally.

Ophthalmoscopically, the hypoplastic disc may appear gray or pale in color and is often surrounded by a yellowish mottled peripapillary halo, bordered by a ring of increased or decreased pigmentation. It is often associated with selective tortuosity of the retinal veins.

It is difficult to predict visual acuity potential on the basis of optic nerve appearance.

Visual acuity ranges from 20/20 to no light perception, and affected eyes show localized visual field defects. Nystagmus may be noted when both eyes are involved. The incidence of strabismus is increased with ONH. Electroretinography is normal in the majority of patients.

Optic nerve hypoplasia is frequently associated with other CNS anomalies, such as septum pellucidum absence, agenesis of corpus callosum, cerebral hemisphere abnormalities, or pituitary gland abnormalities. Septo-optic dysplasia (De Morsier syndrome) is used to describe the association between optic nerve hypoplasia and the absence of septum pellucidum and agenesis of the corpus callosum.

Most cases of ONH have no clearly identifiable cause but hypoplasia has been associated with maternal diabetes, maternal alcohol and drug abuse, maternal use of anti-epileptic drugs, and young maternal age (20 years of age or less).