Visual Disturbances



Visual Disturbances


Jeffrey G. Odel

Julia Mallory



INTRODUCTION

No symptom may be as disturbing or dramatic to a patient as acute visual loss. Although acute ocular diseases such as glaucoma, uveitis, and retinal detachment may require urgent evaluation by an ophthalmologist, a high percentage of visual disturbances fall within the province of the neurologist. Neurologic visual symptoms may be reported as blurriness, focal obscurations, or positive visual phenomena. Because the visual pathway from the retina to the calcarine cortex is constant from individual to individual, anatomic localization can be made with a high degree of accuracy on physical examination. The progression, associated symptoms and signs, and clinical setting will help you make the correct diagnosis and suggest the proper acute management.


NEUROANATOMY

The optical system of the eyes focuses images onto the outer retina where the light energy is converted into nervous impulses by rods and cones. These impulses are then conveyed by the axons of the retinal ganglion cells on a path centripetally through the inner retina, converging on the optic nerve head. The impulses then travel along the optic nerve and through the optic chiasm where fibers from the nasal retina (temporal visual field) decussate to join temporal retinal fibers (nasal visual field) from the other eye in the contralateral optic tract. The retinal ganglion cell axons pass from the optic tract into the geniculate body where they synapse. The nervous impulse is conveyed by the geniculocalcarine pathway, composed of the axons from the geniculate body cells that pass through the temporal and parietal lobes, to synapse in the calcarine cortex in the occipital lobe which relays the impulses for higher cortical analyses such as reading and recognition.






FIGURE 9.1 Visual field cuts produced by lesions at different points along the visual pathway. (a) Monocular segment anopia produced by a retinal artery branch occlusion in the left eye. (b) Monocular blindness produced by a lesion in the left optic nerve. (c) Bitemporal hemianopia produced by a mass lesion at the optic chiasm. (d) Right segment anopia produced by a lesion in the lateral geniculate body of the left thalamus. (e) Right upper quadrantanopia produced by a lesion in the left temporal optic radiation (Meyer loop). (f) Right lower quadrantanopia produced by a lesion in the left parietal optic radiation. (g) Left homonymous hemianopia produced by a lesion in the calcarine cortex of the right occipital lobe. Note that macular vision is sometimes spared because of middle cerebral artery collateral blood flow to the occipital pole. OS, oculus sinister; OD, oculus dexter. (Adapted from Marshall R, Mayer S. On Call Neurology. 3rd ed. Philadelphia: Saunders; 2007.)


COMMON PROBLEMS

Visual loss may be due to abnormalities of the ocular media, the retina, the anterior visual pathway (the optic nerves, chiasm, and optic tracts), or the geniculocalcarine pathway (Fig. 9.1 and Table 9.1).
It may also result from a lesion in the oculomotor or vestibular systems from diplopia or oscillopsia. Patients with alexia or agnosia may also complain of visual loss, although their acuity may test normally.








TABLE 9.1 Signs and Symptoms that Suggest Location in the Visual Pathway






























Location of Lesion along Visual Pathway


Signs and Symptoms


Anterior segment of the eye




  • Blurred vision



  • Glare or halos



  • Foreign body sense in eye



  • Correction with squinting, pinhole, or ophthalmoscope



  • Response to blinking



  • Visible opacities on exam


Retina




  • Metamorphopsia



  • Macropsia or micropsia



  • Positive scotoma



  • Geographic scotoma



  • Central scotoma unconnected to blind spot



  • Prolonged photostress recovery time



  • Flashes or floaters



  • Nyctalopia or hemeralopia



  • Purple, yellow, or green vision


Optic nerve




  • Negative scotoma



  • Decreased brightness and/or color sense



  • Cecocentral, arcuate, or altitudinal visual field defect or horizontal step in visual field



  • Relative afferent pupillary defect



  • Optic disc swelling or atrophy



  • Nerve fiber layer dropout



  • Optic nerve head cupping


Chiasm




  • Bitemporal hemianopia



  • Band atrophy of optic disc



  • Postfixation blindness



  • Hemifield slide phenomena


Optic tract




  • Homonymous hemianopia with optic atrophy and relative afferent pupillary defect in contralateral eye


Geniculate body




  • Congruent horizontal homonymous sectoranopsia



  • Congruent upper and lower sectoranopsias



  • Incongruent homonymous hemianopia



  • Optic atrophy


Geniculocalcarine pathway




  • Homonymous hemianopia



  • “Pie-in-the-sky” hemianopia, temporal lobe



  • “Pie-on-the-floor” hemianopia, parietal lobe



  • Optokinetic defect ipsilateral to parietal lobe lesion



  • Scotomatous hemianopia—occipital lobe



  • Preserved temporal crescent of field—occipital lobe



  • Hemiparesis, aphasia, alexia, agnosia, somatosensory disturbance


Oculomotor/vestibular system




  • Oscillopsia



  • Diplopia



BLURRED VISION

Refractive errors, as in myopia, hyperopia, and astigmatism, cause blurred vision. This blurring may be corrected by having the patient focus through an ophthalmoscope by turning the lens wheel either at distance or with a reading card held at 14 inches. If the ophthalmoscope fails or is not available, having the patient view through a pinhole (with an optimum diameter of 2 mm) corrects most refractive errors. Cataract and corneal edema or opacity may cause glare, halos, or light beams from lights. Tear film disturbance, or dry eye, responds to blinking or artificial tears. Opacities of the ocular media, as in cataract, corneal scar, or aqueous or vitreous hemorrhage, may be visualized during examination using an ophthalmoscope while focusing on the red reflex in the pupil. Opacities anterior to the center of the eye in the cornea, anterior chamber, and lens rise when the patient looks up slightly, whereas those in the posterior half of eye (vitreous) descend.


VISUAL DISTORTIONS

Retinal pathology that distorts the retina may cause straight lines to appear bent, broken, or curved (metamorphopsia) or objects to appear small (micropsia) or large (macropsia). This is caused by distortion of the outer retina by detachment, edema, fibrosis, neovascularization, or hemorrhage. Vitreous traction on the retina will cause photopsias if the vitreous detaches from the retina or vitreous traction tears or pulls a hole in the retina; floaters may be seen.

Retinal detachment will occur if fluid accumulates under the retina because of a hole or tear and would be appreciated as a shadow or curtain over the eye. With disease of the rods, as in retinitis pigmentosa or vitamin A deficiency, the patient experiences night blindness (nyctalopia) and prolonged dark adaptation. Impaired vision in daylight (hemeralopia) suggests cone dysfunction as in cone dystrophy but may be seen with central visual field defects of optic nerve origin. Central scotomas (areas of depressed visual sensitivity surrounded by areas of higher sensitivity) so small as to be unconnected to the blind spot are almost only seen in retinal conditions (Fig. 9.2A). Central ring scotomas are also a strong indicator of a retinal process (Fig. 9.2B).

Impaired visual recovery following bright light exposure suggests a retinal process. Purple vision suggests poor oxygenation to the outer retina from ipsilateral high-grade carotid stenosis or poor choroidal perfusion from giant cell arteritis; this can also be seen in central serous chorioretinopathy. Yellow, green, or snowy vision suggests retinal toxicity from digitalis toxicity. A dark blotch, positive scotoma, suggests a retinal process particularly if associated with photopsia. With visual loss of ocular origin, there may be associated local symptoms or signs, such as pain, photophobia, redness, or soft-tissue swelling.







FIGURE 9.2 Examples of visual field loss. Areas in red denote the physiologic blind spot created by the optic disc. Areas in blue denote pathologic visual loss. A: Bilateral small central scotomas at the fovea indicating a retinal condition. B: Bilateral central ring scotoma also strongly indicative of a retinal condition. C: Bilateral cecocentral scotomas, as in optic neuropathy. D: Left eye: paracentral defect. Right eye: paracentral defects that have coalesced to an arcuate defect. E: Left eye: nasal horizontal step field defect. F: Left eye: junctional scotoma of Traquair. G: Left eye: cecocentral defect ipsilateral to the affected left optic nerve. Right eye: junctional temporal defect in the contralateral (right) eye. H: Variation of BTH as in pituitary adenoma or meningioma attacking the chiasm from above.


VISUAL FIELD DEFECTS


Retinal Nerve Fiber Bundle Defects

The retinal nerve fiber bundle path is determined by the fovea, which is the center of the macula; the optic disc, which is centered about 15 degrees nasal to the fovea slightly above the horizontal; and the horizontal retinal raphe. Fibers coming from the retina temporal and superior to the foveal center arc above the macula, entering the superior optic disc; those temporal and inferior to the center of the fovea arc below the macula and enter the optic disc inferiorly (Fig. 9.3).

This divergent pathway of the superior and inferior axons in the temporal retina around the macula creates the horizontal retinal raphe in the temporal retina and is the anatomic correlate of the nasal horizontal step field defect (Fig. 9.2E). These defects are more marked in the nasal visual field typically closer to fixation nasally and show respect for the horizontal meridian. Axonal damage may occur in the retina, disc, or retrobulbar optic nerve, as the nerve bundles stay together anterior to the chiasm. The axons from
the nasal fovea and axons originating between the fovea and the disc course directly into the temporal disc, and damage to these axons results in a cecocentral scotoma (Fig. 9.2C). This bundle then occupies the center of the optic nerve anterior to the chiasm. Damage to fibers coming from the retina nasal to the disc leads to temporal sectoral defect with an apex at the blind spot.






FIGURE 9.3 Retinal nerve fiber anatomy of a right eye as seen on opthalmoscopy, with the optic disc nasal to the fovea, which is the center of the macula. PM is the papillomacular bundle of fibers that carry visual impulses nasally directly from the macula to the optic disc. HR is the horizontal retinal raphe. Nerve fibers arising from the retina temporal to the fovea arch above and below the macula and PM, and insert into the superior and inferior poles of the optic disc respectively. These arcuate paths of fibers from the temporal retina (nasal visual field) are responsible for the characteristic visual field defects of optic nerve disease, including peripheral horizontal nasal steps, arcuate defects, and cecocentral scotomas.


Symptoms and Signs of Optic Nerve Defects

The hallmarks of optic nerve dysfunction are visual field defects, loss of brightness and color sense, decreased pupillary reaction to light, optic nerve head swelling or optic atrophy, and nerve fiber layer dropout. Optic neuropathy causes cecocentral visual field defects (see Fig. 9.2C), paracentral defects (see Fig. 9.2D left eye), arcuate visual field defects (see Fig. 9.2D right eye), nasal step defects (see Fig. 9.2E left eye), and altitudinal defects (see Fig. 9.2E right eye).

In optic neuropathy, the shape of visual field defects corresponds to the path of the arcuate and macular-papillary nerve fiber bundles. Paracentral defects, the smallest defects in the arcuate region may coalesce to form arcuate defects (Fig. 9.2D) as in glaucoma.

Injury of nasal optic nerve fibers anywhere from the back of the eye to just anterior to the chiasm will produce an ipsilateral relative temporal visual field defect that does not respect the vertical meridian. A small lesion right at the nasal junction of the optic nerve and chiasm may result in an ipsilateral central temporal defect that respects the vertical meridian, the monocular junctional scotoma of Traquair (Fig. 9.2F). Injury of temporal fibers of the optic nerve between the optic canal and the chiasm will produce a relative ipsilateral nasal defect that does not respect the vertical. More marked junctional involvement of the optic nerve and chiasm may produce a cecocentral defect ipsilateral to the involved optic nerve and an upper temporal defect in the contralateral eye (Fig. 9.2G). Thus with loss of vision in one eye, it is critical to check the other eye to look for an unsuspected temporal visual field defect, as this is frequently caused by a mass lesion such as a pituitary adenoma or meningioma.


Chiasmal Defects

Chiasmal involvement leads to variations of bitemporal hemianopsia (BTH) due to damage to crossing fibers from the nasal retinas, which carry information from the temporal visual fields. Tumors that compress the chiasm from below produce BTH that is greatest superiorly (Fig. 9.2H). Lesions attacking the chiasm from above, such as craniopharyngiomas, produce BTH that starts inferiorly (Fig. 9.4A) The visual field defect of lateral chiasmal compression (typically due to an aneurysm) spares the ipsilateral superior temporal visual field, causing visual loss in the other three ipsilateral quadrants and in the contralateral superior temporal quadrant (Fig. 9.4B).


Optic Tract Defects

Lesions of the optic tract (the continuation of the optic nerve relaying signals from the optic chiasm to the ipsilateral lateral geniculate nucleus) produce contralateral incongruent homonymous hemianopsias. These may have elements of chiasmal involvement and are accompanied by optic atrophy. The eye with more visual field loss, typically the contralateral eye, may exhibit a relative afferent pupillary defect. The pattern of optic atrophy is band or bow tie shaped in the eye with the temporal field defect; it is more generalized in the eye with the nasal defect. Some examiners have found congruous homonymous hemianopias in tract lesions.


Geniculate Body Defects

Geniculate body lesions may cause incongruous or congruous visual field defects. Tumors of the geniculate body produce incongruous homonymous hemianopias. There are two syndromes of geniculate infarction that result in striking congruous defects. Lateral posterior choroidal artery infarction results in a congruous horizontal homonymous sectoranopia, (Fig. 9.4C), a wedge-shaped hemianopia along the horizontal with the apex pointing to fixation and the wedge spreading out to the contralateral periphery. Anterior choroidal artery occlusion results in upper and lower homonymous sectoranopias that spare the horizontal and are complementary in shape to the horizontal homonymous sectoranopia (Fig. 9.4D). Because the optic tract synapses in the geniculate body, optic atrophy may be observed several weeks after a geniculate lesion.


Hemispheric Defects

Homonymous hemianopias are caused by lesions of the geniculocalcarine pathway in the temporal, parietal, or occipital lobes. Traditionally, the more posterior the site of a lesion, the more congruous it was thought to be, with occipital lesions being highly congruous. Recently, however, the rule of congruity has been questioned due to radiographic verification that shows congruous hemianopias at all retrochiasmal locations, even in the optic tract. “Pie-in-the-sky” upper quandranopias that do not respect the horizontal suggest a temporal lobe location (Fig. 9.4E), whereas hemianopias that are greatest inferiorly suggest a parietal localization (Fig. 9.4F). This is especially true when accompanied by a defect in optokinetic nystagmus with targets following to the side of the lesion. The extinction phenomenon is an apparent hemianopsia in a seeing area of the visual field that occurs during simultaneous stimulation to right and left hemifields. Extinction can be confirmed by finding a similar defect to tactile simultaneous stimulation that is not present on single-sided stimulation.

Homonymous hemianopic scotomas suggest occipital lesions but are not specific for that location (Fig. 9.4G). Involvement of the calcarine cortex (or primary visual cortex, V1, Brodmann area 17),
anterior in the occipital lobe, where peripheral vision is represented, results in a monocular temporal crescent visual field defect. After a retinal detachment has been ruled out, this is specific for an occipital lobe lesion contralateral to the field defect and is usually caused by a tumor. Sparing of the anterior calcarine cortex is common in infarcts of the posterior cerebral artery and results in a preservation of the temporal crescent contralateral to the lesion. It is highly suggestive of occipital localization. A homonymous hemianopia with sparing of the central visual field is referred to as macular-sparing hemianopsia (Fig. 9.4H) and is suggestive of occipital involvement but macular sparing has been reported as anterior as the optic tract. Preservation of motion vision in a hemianopic defect, termed the Riddoch phenomenon, is also suggestive of occipital involvement, although it has also been seen as far anteriorly as the optic tract as well. Anton syndrome, denial of blindness in the setting of bilateral hemianopsias, represents bilateral calcarine
involvement plus an association area infarction. Quadrantic visual field defects precisely respecting the horizontal meridian in each eye have been reported in extrastriatal occipital cortex lesions involving areas V2/V3.






FIGURE 9.4 Examples of visual field loss. Areas in red denote the physiologic blind spot created by the optic disc. Areas in blue denote pathologic visual loss. A: Variable bitemporal inferior quadrantanopsia attacking the chiasm from below. B: Variable bilateral visual field defects from a right lateral chiasmal compression from an aneurysm. C: Bilateral congruous horizontal homonymous sectoranopia resulting from lateral posterior choroidal artery infarction. D: Upper and lower homonymous sectoranopias that spare the horizontal as in anterior choroidal artery occlusion. E: Bilateral pie-in-the-sky upper quadranopias from a temporal lobe lesion. F: Hemianopia greater inferiorly from a parietal lesion. G: Homonymous hemianopic scotoma suggesting but not specific for occipital lesion. H: Macular-sparing hemianopsia suggesting but not specific for occipital lesion.


DIPLOPIA

Disturbances of eye movement and ocular alignment result in diplopia. This can result from ocular muscle problems, neuromuscular transmission defects, cranial neuropathies, and ocular motor nuclear and internuclear ophthalmoplegias and cause double vision, which the patient may report as blurry vision. Damage to the central vertical and horizontal gaze pathways and vestibular systems may result in gaze palsies or nystagmus that the patient may report as visual difficulty.


CAUSES OF VISUAL LOSS

Visual loss may be fleeting (unilaterally or bilaterally), acute and slowly remitting, slowly progressive, acute and nonremitting, or acute with ophthalmoplegia. The tempo of visual loss provides important clues regarding etiology.


TRANSIENT MONOCULAR BLINDNESS

Also known as Amaurosis fugax (AF), transient monocular blindness (TMB) may be complete or partial and lasts from seconds to 20 minutes with recovery. The most frequent cause is thromboembolism of the retinal artery, but many other conditions can cause the syndrome as well (Table 9.2).


Embolic Transient Monocular Blindness

TMB from embolism is frequently described as a descending curtain that covers all or half of the field of vision or may start with quadrant involvement. Less frequently, it is reported as an ascending curtain and rarely, as a sideways moving blind. It may appear as a ground glass, a gray-out, a cloud, or complete blackness. Swirling sparks of light, signifying emboli that are entopically stimulating the retina as they course through the retinal vessels, may occur. TMB may clear like a clearing fog or regress like a curtain that goes up or down, altitudinally or quadranopically. This pattern of AF suggests embolic origin most frequently from an ulcerative plaque of the carotid bifurcation or originating from the ascending aorta or heart. These cases require emergent evaluation.








TABLE 9.2 Causes of Transient Unilateral Visual Loss





























  • Embolism




  • Hypotension




  • Arterial spasm




  • Recurrent erosions of the cornea or corneal basement membrane dystrophy




  • Angle-closure glaucoma




  • Hyphema




  • Vitreous hemorrhage




  • Optic nerve head drusen




  • Congenital optic nerve anomalies (coloboma, morning glory disc)




  • Orbital masses (causes gaze-evoked monocular visual loss)




  • Uhthoff phenomenon




  • Asymmetric light adaptation



Hypotensive Transient Monocular Blindness

Hypotensive TMB usually occurs in the setting of extensive arterial occlusive disease. Hypotensive AF may range from being very brief to lasting longer than embolic AF. The episodes may present with monocular concentric constriction, or blotchy vision, or bright objects appearing brighter, loss of contrast, or photographic negative vision. Bright light may provoke hypotensive TMB, and there may be prolonged photostress recovery of vision. It may be associated with ocular ache and mild signs of cerebral ischemia such as poor concentration, sudden fatigue, or feeling faint. Hypotensive TMB may be precipitated by arterial hypotension, arrhythmias, or venous hypertension. Bending over, standing up, exercising, bright light, and overheating may also precipitate attacks. Giant cell arteritis, Takayasu disease, and other occlusive disorders of the aortic arch or carotid arteries may also be present.

During an attack of hypotensive TMB, the retinal vessels on ophthalmoscopy may be narrow and the disc blanched; just following an attack, the vessels dilate with irregularity of the veins and hyperemia of the disc. Between attacks, the retina may have midperipheral and peripheral retina dot and blot hemorrhage at the end of vessels, venous tortuosity, and microaneurysms. This is referred to as venous stasis retinopathy and can be differentiated from vein occlusion by the presence of arterial pulsations spontaneously or with light pressure on the globe.


Arterial Spasm

Arterial spasm in the ophthalmic, retinal, or choroidal circulation may result in TMB in the adolescent or young adult who is otherwise healthy. The description of the visual loss is varied but does not involve a curtain falling over the vision. It more closely mimics the description of hypotensive TMB with blotchy visual loss of several minutes’ duration. Previously, it was referred to as retinal migraine; however, its relation to migraine is now less certain.

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Jul 27, 2016 | Posted by in NEUROLOGY | Comments Off on Visual Disturbances
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