Each year at least 0.9% of GP consultations involve eye conditions.1 Among these consultations, diplopia (double vision) is an uncommon but important eye symptom, although data on its incidence in general practice are lacking. While some types of diplopia may be due to refractive or ocular surface abnormalities, such as uncorrected astigmatism and corneal irregularities, it may also represent more concerning neurological disease.2 The challenge for GPs is identifying when diplopia is a sign of a serious condition requiring urgent referral. This article considers the presentation of new-onset diplopia, how to differentiate its causes, and practical steps for decision making in the community.

Diplopia is the perception of two images of a single object, whether separated vertically, horizontally, or obliquely.3 The history is key as patients may not report ‘seeing double’. Indirect complaints include ‘blurred vision’, ‘eye strain’, or even ‘dizziness’. A thorough history, including onset, frequency, associated symptoms (for example, headache or ptosis), and exacerbating or relieving factors, can provide crucial information.2

Key points to ascertain from the history are:

Is the double vision monocular (that is, persisting when one eye is covered) or binocular?

Is the image separated vertically, horizontally, or obliquely?

Is the onset of the double vision recent, or is there a history of a previous, self-resolving episode? (This is significant as it is suggestive of myasthenia gravis.)

Is the diplopia constant or intermittent?

Are there associated signs, for example, ptosis and ocular muscle weakness, or significant variability in symptoms?

Are …