If input to the brain from both eyes is equal, irrespective of whether they are normal, pupillary constriction will be the same whichever eye is illuminated. 5 An RAPD is detected using the swinging torch test, in which the pupils are alternately illuminated by a light source while the patient gazes at a distant object to eliminate accommodation. In these cases, a relative afferent pupillary defect (RAPD) can generally be elicited. Systemic vascular disease (including giant cell arteritis) as well as a pituitary tumour compressing one optic nerve should both be considered in the differential diagnosis. Any form of orbital tumour that compresses the optic nerve can also cause transient monocular loss, and the visual loss can sometimes be gaze-evoked in this setting. Red flags and appropriate referral pathways for transient visual loss are discussed in Table 1. Other ocular causes of transient monocular vision loss include incipient retinal vascular occlusion, retinal vasospasm and tear film instability.
These events may be precipitated by pupil dilation in the dark or, rarely, the use of dilating eye drops. 2 Within the eye, acute angle-closure glaucoma can cause transient unilateral visual phenomena which are often, but not always, associated with ocular pain and redness. The aetiology of transient vision loss in one eye may relate to pathology in the eye, optic nerve, brain, neck or heart.
#Monocular vs binocular vision full#
1 A full neurological examination is recommended for all patients with unexplained transient vision loss. 3 It is important to ask about previous migraines, transient ischaemic attacks or strokes, and neck trauma. It is important to ask about associated visual and/or neurological symptoms, including haloes around lights, diplopia, headache, nausea, vomiting, photophobia or phonophobia. 4 It is crucial that a thorough history-taking includes an attempt at determining whether one or both eyes were affected as well as discovering the speed of onset, any precipitating factors, the speed of recovery and the presence of any residual symptoms.
2 In contrast, the most common cause of transient binocular vision loss is migraine. The most common cause of monocular transient vision loss is amaurosis fugax, usually resulting from an embolic complication of an ulcerated plaque of the carotid artery. An alternative is to ask whether the visual world was split (eg seeing half a face), as this almost always implies binocular visual loss. One way to do this is to ask whether the patient covered an eye while the problem was happening. It is essential that the clinician distinguishes whether the presentation is for monocular or binocular vision loss. It may be difficult for a patient to distinguish monocular from binocular transient vision loss, and this is often reflected in the history. 2,3 This review aims to guide initial management and suggest referral pathways in both of these situations. Alternatively, new-onset transient vision loss may be an early sign of a sight-threatening, and possibly life-threatening, emergency. 1 Medical practitioners may become aware of previous episodes of transient vision loss while taking a patient’s history for a seemingly unrelated problem. The aetiology may be localised to the eye, orbit, optic nerve, brain, neck or heart through careful history-taking and examination. Transient vision loss may be monocular or binocular.
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