ABC of eyes. Acute visual disturbance.

In assessing a patient who has experienced an acute disturbance of vision in an uninflamed eye an accurate history is crucial, because it may be that a longstanding visual defect has only just been noticed by the patient. It is important to make this differentiation as this alters the range of diagnoses and the urgency of treatment. Acute visual disturbance ofunknown cause requires urgent referral. In many cases the diagnosis may be made from the history. Symptoms of floaters or flashing lights suggest a vitreous detachment, a vitreous haemorrhage, or a retinal detachment. Horizontal field loss usually indicates a retinal vascular problem, whereas a vertical defect suggests an abnormality posterior to the optic chiasm. If there is central field loss ("I can't see things in the centre") there may be a disorder at the macula. Associated symptoms such as headache may indicate giant cell arteritis or migraine. The visual acuity gives a strong clue to the diagnosis. A total lack of perception of light indicates complete occlusion of either the central retinal artery or the arteries supplying the head of the optic nerve. The nature of the field defect gives clues as outlined above. Obstruction of the red reflex on ophthalmoscopy suggests a vitreous haemorrhage, although the patient may have a pre-existing cataract. The appearances of the macula, remaining retina, and head of the optic nerve will indicate the diagnosis if there has been a haemorrhage or arterial or venous occlusion in these areas.