Disturbances of vision

Published on 10/04/2015 by admin

Filed under Neurology

Last modified 22/04/2025

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Disturbances of vision

Common visual symptoms are loss of vision, blurring of vision or loss of part of the visual field. Occasionally more complex disturbances such as hallucinations or inattention may occur. Loss of vision may affect one eye or one visual field and patients may misinterpret this, for example mistaking a right homonymous hemianopia for a defect of vision in the right eye. It is important to establish which they mean, in order to decide which part of the visual pathway is affected (Fig. 1). The timing, evolution and duration of visual loss are crucial in diagnosis.

image

Fig. 1 Visual pathways with sites of lesions marked.

Monocular visual loss

Monocular visual loss may be due to a lesion affecting one eye or the optic nerve anterior to the optic chiasm. The pupil response is usually normal in disease of the eye itself but is usually impaired in optic nerve disease, either as a complete or relative afferent pupillary defect (p. 14).

Acute reversible monocular visual loss

Amaurosis fugax causes sudden, reversible loss, lasting up to 30 min with complete and rapid recovery. It is usually due to embolism from the ipsilateral carotid artery to the retinal artery but may be associated with other causes of a transient ischaemic attack (TIA; p. 70). The patient describes a curtain coming down over their vision and episodes often recur. Typically the patient has no ocular signs at the time of being seen, but there may be cholesterol plaques from fragmented emboli in the retinal arterioles or carotid bruits to support the diagnosis. This should be investigated as a carotid artery TIA because there is a risk of subsequent middle cerebral artery infarction.

Retinal migraine occasionally occurs in younger patients. The episodes usually have a more gradual onset and last longer. There may also be a typical migraine headache.

Acute (closed angle) glaucoma can produce transient visual loss, occasionally without pain, although there will often be a typical history of coloured halos in vision preceding loss. Diagnosis requires ophthalmological assessment.

Optic neuritis usually occurs in young adults. It causes a visual loss that commonly evolves over 3–10 days then gradually improves over days to weeks. There may be pain behind the eye and flashing lights on eye movement. In the acute phase, the optic disc may look pink, but then it becomes pale and atrophic with reduced colour vision and visual acuity, and a relatively afferent pupillary defect. It may be an isolated inflammatory lesion, but over half go on to develop multiple sclerosis.

Acute-onset, persistent monocular visual loss

Anterior ischaemic optic neuropathy evolves over minutes to days. An altitudinal field defect, where the upper or lower half of the visual field is lost, is characteristic; patients feel as if they are looking over a wall. There is often optic nerve head swelling with some fundal haemorrhages. In patients under the age of 55 years, this is likely to be due to atheromatous disease, but in older patients, it may be due to giant cell arteritis (GCA). In both types, the condition may spread rapidly to affect both eyes but it is especially urgent to diagnose GCA because it is treatable with high-dose corticosteroids. There is usually associated headache and weight loss and an elevated blood erythrocyte sedimentation rate (ESR) or plasma viscosity. An urgent temporal artery biopsy confirms the diagnosis in 60–80% of cases but treatment should not wait for results of the biopsy (p. 40).

Ocular causes of sudden-onset visual loss include retinal detachment, vitreous haemorrhage and retinal vein thrombosis (p. 17).

Progressive monocular visual loss

This is commonly due to diseases of the eye, including senile macular degeneration in the elderly, diabetic retinopathy and chronic (open angle) glaucoma with a typical arcuate field defect.

Optic nerve disease occasionally causes progressive visual loss, most commonly from compression by meningiomas or gliomas of the optic nerve. There is progressive reduction in acuity and typical signs of optic nerve disease (Table 1).

Table 1 Types of visual loss

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Binocular visual loss

Almost any process that causes unilateral visual loss may affect both eyes or optic nerves. Some patients may not notice disease of one eye while the other remains normal and it is only when the remaining eye deteriorates that they become aware of a defect, especially with chronic processes such as glaucoma.

In these patients, the defect is usually asymmetrical. Bilateral optic nerve lesions cause optic atrophy, reduced acuity, incongruous field defects with central scotomas that cross the midline, colour desaturation and abnormal pupil responses. Common neurological causes are optic neuritis and idiopathic intracranial hypertension (p. 40).

Unilateral retrochiasmal lesions produce field defects in both eyes that are homonymous (usually hemianopias or quadrantanopias) and respect the midline, with preserved visual acuity and usually normal pupil responses.

Acute bilateral visual loss

Causes of acute bilateral visual loss include pituitary lesions, temporal arteritis or other ischaemic optic neuropathy, acute demyelination, Leber’s optic atrophy, bilateral intraocular disease (e.g. anterior uveitis) and bilateral occipital infarction (cortical blindness), sometimes as part of basilar artery thrombosis. Because pupillary responses are preserved in cortical blindness, these cases are sometimes misdiagnosed as hysteria.

Slowly progressive binocular visual loss

Chiasmal lesions commonly cause a bitemporal hemianopia, but if the lesion is not exactly central, the involvement of one eye may be greater than of the other. The field defect is often clearest on testing the central field to red pin. There is frequently reduced acuity and there may be optic atrophy. The most common cause is a benign pituitary adenoma and there may be associated endocrine disturbance (p. 96).

Symmetrical anterior visual pathway disturbance occurs in toxic or metabolic causes of optic atrophy such as vitamin B12 or folate deficiency and tobacco–alcohol amblyopia and in some degenerative conditions, for example retinitis pigmentosa. Because of the symmetry, a relative afferent pupillary defect (RAPD) may not be demonstrable.

Slowly progressive hemianopic defects usually reflect tumours of the retrochiasmal visual pathways.

Other visual disturbances

Inattention to the contralateral visual field without a field defect

This occurs in lesions of the parietal lobe, especially on the right. Patients tend to ignore stimuli presented to the left visual field, especially with simultaneous right-sided stimuli. When asked to draw a clock, they typically miss the numbers from 6–12, or squash all the numbers into the right half.

Agnosia

This is the inability to recognize or categorize objects presented visually in the presence of normal acuity. The objects may be identified immediately if palpated. Inability to recognize faces (prosopagnosia) is commonly part of the condition. It is usually due to bilateral visual cortex disease.

Visual hallucinations

These may be due to lesions in any part of the visual system. They may be simple patches of colour or light, or complex images. They are most commonly seen in migraine or epilepsy but may occur in any visual disturbance, usually being restricted to the abnormal visual field. They may also be part of an encephalopathy (p. 52).

Some investigations of visual disturbance

image Neuroimaging. MRI is the best modality for imaging the optic chiasm or optic nerve; views are as indicated.
image The visual fields can be charted using several techniques, both manual and computerized.
image Visual evoked potentials can give information about optic pathway function, especially optic nerve demyelination.

Disturbances of vision

image The pattern of visual field loss usually gives the anatomical location of the lesion and the timing gives a clue to the pathology.
image Pupillary responses to light and visual acuity are normal with lesions posterior to the optic chiasm.
image Lesions of the optic nerve cause reduced visual acuity, central scotomas, reduced colour vision and abnormal pupillary responses.
image Lesions of the chiasm may be best detected on testing fields to red pin.
image Neuroimaging investigation needs to be tailored to the region of interest.

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