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.
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.
