Some Diseases Of The Visual System Retina and Optic Nerve Lesions

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Retrobulbar Neuritis Retrobulbar neuritis typically presents in young adults, with onset over 24-48 hr, a large central scotoma, and a painful eye on palpation and movement. There may be a past history of episodes of multiple sclerosis or this illness may be the first manifestation of it. The fundus is usually normal. Afferent pupillary defect is commonly present.

Optic Neuritis The presentation of optic neuritis is like that of retrobulbar neuritis, except that it may be painless. The terms retrobulbar neuritis and optic neuritis are used interchangeably. Edema of the optic nerve head may be present. (See the section on papillitis in Chapter 3.)

Central Serous Retinitis Central serous retinitis has subacute onset (days) of slight to moderate vision loss in one eye, usually in a male patient aged 20-40. The disease is caused by fluid exudate lifting the retina, usually at the macula. The patient complains that objects look smaller with the affected eye.

Giant Cell Arteritis of the Central Retinal Artery This disease occurs in those age 60 or older, with a sudden onset of central blindness. Superficial temporal arteries are typically tender, pulseless, and tortuous. There is almost always an elevated erythrocyte sedimentation rate and a low-grade fever. The history will often contain complaints of headache and stiff, aching, weak shoulder and hip muscles. Funduscopy shows total retinal ischemia (see the following section). Diagnosis, including temporal artery biopsy, is an emergency.

Anterior Ischemic Optic Neuropathy In patients over age 50, anterior is-chemic optic neuropathy is a manifestation of giant cell arteritis, vasculitis, diabetes mellitus, or Takayasu's disease or is frequently idiopathic. There is a sudden onset of visual loss, sometimes followed by increasing and progressive visual failure over 5-7 days. Altitudinal (inferior) field defects are common. Funduscopy examination shows a swollen disc, hemorrhages near the disc edge, and cotton-wool spots. A macular star is common with vascu-lopathies. The other eye is commonly involved within weeks or months of the first eye.

Retinitis Pigmentosa The most common symptom of retinitis pigmentosa (RP) is night blindness. The onset and severity of symptoms depend on the pattern of inheritance: the autosomal recessive type presents earliest and is the most severe, X-linked is intermediate, and autosomal dominant is frequently mild. The fundus shows black "bone spicules" of pigment clustered around vessels in the midperiphery. The disc is waxy pale, and there is attenuation of both retinal vessels. Visual fields show ring-shaped arcuate or annular scotomas.

Pseudoretinitis Pigmentosa Pseudoretinitis pigmentosa refers to the fundus findings of a number of disorders that mimic RP. Some pigmentary retinopathies that are not RP are those following congenital and acquired syphilis, childhood exanthemas, phenothiazine usage, and trauma.

Atypical RP includes sectoral RP (fundus changes in one sector of the fundus bilaterally, which can mimic chiasmal lesions) and pericentral RP (fundus changes central). Unilateral RP probably does not exist.

Diseases and syndromes associated with RP are Bassen-Kornzweig, Bardet-Biedl, Kearns-Sayre, and Usher's.

Glaucoma Glaucoma exists when elevation of intraocular pressure is sufficient to damage optic nerve fibers at the optic disc level. This is the second leading cause of blindness in North America. There are two types: acute angle-closure glaucoma (ACG) and chronic open-angle glaucoma (OAG).

ACG presents with severe pain in the eye and head, blurred vision, and colored halos around lights, plus nausea and vomiting. Pain results from a rapid rise in intraocular pressure. Attacks are precipitated by reduced illumination and may be relieved by sleep, bright light, or miotic agents, all of which constrict the pupil. ACG usually presents unilaterally. The predisposing factors are often bilateral, and the uninvolved eye is therefore at risk. This is an emergency.

OAG is the most common form of glaucoma and is dangerous because the onset is often gradual and asymptomatic. Central vision is preserved until late, and the field loss is often unnoticed by the patient until the disease is well advanced. It is usually a bilateral disease, although asymmetrical.

Visual field defects in glaucoma respect the horizontal division of the visual fields. The arcuate nerve fibers arching above and below the macula from the temporal region are most susceptible to glaucomatous damage. Therefore, the characteristic field defects are paracentral and arcuate nasal scotomas (type 3 in Figure 1-8A). The central area of the visual field is the most resistant, so visual acuity may be normal even in advanced glaucoma.

Optic disc changes are an increase in the diameter and depth of the physiological cup and increased pallor.

Central Retinal Vein Occlusion Central retinal vein occlusion (CRVO) presents with painless, always unilateral, loss of vision. The patient is commonly a young adult. The extent of visual loss is variable, depending on the degree of venous occlusion, the amount of macular edema, and the presence or absence of complications such as retinal neovascularization and neovascular glaucoma.

The fundus shows dilated, tortuous veins; retinal hemorrhages usually in the peripheral retina; and retinal edema. Cotton-wool exudates are usually seen only around the disc. The disc edge is indistinct, although the physiological cup remains visible.

Visual fields reveal a relative central scotoma and acuity is usually 20/100, improving to 20/60 with time if there are no complications.

Branch retinal vein occlusion is most common in the superotemporal branch. Fundus changes are confined to the distribution of the branch, and field loss is segmental.

Hypertension often coexists with CRVO, and associated retinal artery disease is a common finding. A picture similar to that of CRVO may be seen in hyperviscosity syndromes, leukemia, and myeloma.

Retinal Artery Occlusion Retinal artery occlusion (RAO) is accompanied by sudden, painless, unilateral loss of vision. It is commonly discovered by the patient on awakening in the morning and occurs in the stroke-prone age group. If the central retinal artery is involved, vision will be completely lost (no light perception). If a cilioretinal artery is present, an island of central vision will be preserved. Visual loss may be confined to a segment of the field if only a branch of the retinal artery is occluded.

The fundus reveals a gray, opaque, edematous retina with a cherry-red fovea. This is normal choroid contrasted against gray retina. Splinter hemorrhages are rarely seen. Branch arteries may show segmented columns of blood (boxcars). There may be a history of transient monocular visual loss lasting minutes, with altitudinal progression as vision fails, that is, the window blind effect.

Causes of RAO include emboli, thrombosis, giant cell arteritis, and collagen-vascular diseases.

Retinal Detachment Retinal detachment (RD) presents with a history of recurrent flashes or floaters in the same area of the visual field. The patient typically complains of a cloud or curtain obscuring part of the field. It usually starts and is most dense peripherally and extends toward central vision. Visual acuity is normal unless or until the macula detaches. An inferior detachment with a superior field defect can be present for a long time before the patient is aware of it. The fundus shows an elevated retina that is gray and wrinkled and undulates.

The elevation will be appreciated as you rack in progressively more plus lenses (black numbers) on the ophthalmoscope to keep the elevated retina in focus.

The most common predisposing factor to RD is degenerative retinal change (as seen in high myopia). Other causes include trauma; a simple "black eye" history may be significant. Malignant melanoma of the choroid can cause a secondary RD, and the retinal neovascularization of diabetes mellitus may result in a tractional RD.

Macular Degeneration Macular degeneration begins at any age but is most common over 60 years. Slow loss of visual acuity occurs bilaterally and is worse in bright light and better in the dark; recovery of vision is slow after exposure to a bright flash of light. The macula may appear normal initially. There are central and paracentral scotomas. Fluorescein retinal angiography and the Amsler grid are helpful in diagnosis.

Optic Neuropathy Optic neuropathy can occur:

1. Without other diseases (eg, Leber's). The typical patient is a young adult male with loss of central vision in one eye, followed by the other eye in days or weeks, with a positive family history. Characteristic fundus changes in the acute stage are followed by optic atrophy. A central scotoma will become cecocentral with upper nasal breakout.

2. With other central nervous system (CNS) diseases, with one or more of the following: congenital deafness, ataxia, spastic quadriparesis, mental deterioration, polyneuropathy, Friedreich's ataxia, Marie's cerebellar ataxia, and Charcot-Marie-Tooth disease

3. With inborn lysosomal disorders: (a) mucopolysaccharidoses or (b) lipidoses

Optic Atrophy Optic atrophy occurs as a consequence of the foregoing and other diseases, such as methyl alcohol or chloroquine ingestion, isoniazid tox-icity, and any compressive, ischemic, or toxic disorder of the retinal ganglion cell or fiber from the retina to the LGB. This includes papilledema, which, if severe enough or chronic enough, can result in optic atrophy. Diagnosis of the cause is often impossible. Clinical diagnosis of atrophy is dependent on the color and structure of the disc.

The lesion responsible for optic atrophy may be anywhere from the retina to the LGB inclusive.

Chiasmal Lesions The most common visual field defect is bitemporal, either central or peripheral or both.

Be careful and persistent with patients with visual loss. Lesions in the chi-asmal region can be deceptive and extremely chronic. The chronicity and slow progression seem to make the symptoms more acceptable and less demanding. Every neurologist and neurosurgeon has had some bad experience with patients thought to have multiple sclerosis, amblyopia from childhood, low-tension glaucoma, retinitis pigmentosa sine pigmento, or atypical macular degeneration as an explanation for their blindness who eventually turn out to have a chiasmal lesion as the true cause. It does not help the patient to make the diagnosis after the optic atrophy is marked and the acuity is down to 20/200.

Another reminder about chiasmal lesions is the place of exploratory intracranial surgery. Ordinarily, there is no such operation as an exploratory intracranial procedure. However, if an eye and field examination point to a chiasmal lesion, even if the skull x-ray, carotid angiography, computerized tomography (CT) scan, and nuclear magnetic resonance (NMR) studies are all normal, then the next "investigative" step is exploration of the chiasmal area. The neurosurgeon may make the diagnosis of chiasmal arachnoiditis that cannot be treated, but he may find the otherwise undiagnosable 4-mm meningioma, pituitary tumor, or craniopharyngioma.

Finally, lesions of the visual pathways behind the optic chiasma never interfere with color vision (ie, without an accompanying loss of light perception). There are reported examples of defective color appreciation from a parietal cortical lesion, but this is color agnosia, not loss of color vision.

Anterior Chiasmal Syndromes

1. The ipsilateral eye is blind and there is an upper temporal field defect in the contralateral eye. The lesion is shown at a in Figure 2-1A.

Figure 2-1A

2. The ipsilateral eye is blind and there is a central temporal sco-toma in the contralateral eye (The same lesion as in Figure 2-1A).

3. The ipsilateral eye is normal and the contralateral eye is as in Figure 2-1A or B (The same lesion as in Figure 2-1A).

Figure 2-1C

Figure 2-1C

4. The ipsilateral eye has a central scotoma and there is a paracentral scotoma in the temporal field of the contralateral eye (The same lesion as in Figure 2-1A). This can progress to the condition shown in Figure 2-1E.

Figure 2-1D

5. The ipsilateral eye is blind and there is a paracentral scotoma in the temporal field and full peripheral field of the contralateral eye (The same lesion as in Figure 2-1A).

Chiasmal Body Bitemporal peripheral field loss occurs as in Figure 2-2A or central temporal scotomas occur as in Figure 2-2C, or a combination of the two as in Figure 2-2B. Lesions occur as in Figure 2-2D. The lesion is usually below the chiasma (eg, a pituitary tumor).

Figure 2-2A

Figure 2-2B

Figure 2-2C

Lesion area related to fields 2.2A to 2.2C

Lesion area related to fields 2.2A to 2.2C

Suprasellar lesions (eg, craniopharyngioma, aneurysm, meningioma, chordoma, or third ventricle distention) can start with a central or peripheral temporal defect that initially may be most marked inferiorly as in Figure 2-2E.

Figure 2-2E

Any of these lesions (suprasellar or infrasellar) may eventually produce the field defect shown in Figure 2-2F.

Figure 2-2F

Posterior Chiasma Posterior chi-asma presents usually with a bitemporal central scotoma with peripheral defects as well, as in Figure 2-3A. A central scotoma usually occurs first. The lesion is shown at a in Figure 2-3B. When big enough to involve the tract at b, a homonymous, hemianopic defect is added.

Figure 2-3A

Lateral Chiasma Lateral chiasmal lesions present with nasal field defects. Very rare, they can be unilateral as in Figure 2-4A or bilateral as in Figure 2-4B. The defect rarely comes up to the midline. Unilateral nasal defects have been reported as a result of infarction of the optic nerve, aneurysm, pituitary tumor, and ectatic carotid artery. Bilateral nasal defects have been reported resulting from chi-asmal arachnoiditis and secondary to obstructive hydrocephalus and pressure from above from the third ventricle. Glaucoma is probably the most common cause of nasal field defects.

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