In the absence of obvious ptosis, a history of intermittent ptosis should be identified. Periorbital pain or pain on eye movements may be indicative of inflammatory causes. Myasthenia gravis should be considered if diplopia is aggravated by intensive use of the eyes, has a tendency to worsen towards the end of the day, and is improved with rest. Exacerbating and relieving factorsīlinking can improve monocular diplopia from corneal astigmatism or simply dry eyes, whereas it has no effect on cataract or macular diseases. Intermittent diplopia with associated ptosis and diurnal variation is suggestive of a neuromuscular junction disorder, such as myasthenia gravis. On the other hand, progression or change of the pattern of diplopia usually indicates ongoing pathology such as a compressive lesion. Diplopia that reaches the maximum image separation instantly and improves spontaneously is usually caused by a single event, often presumed to be vascular. Progression and the temporal sequence of symptoms provide much useful information. Therefore, an abrupt onset of diplopia does not necessarily imply a vascular cause. The onset of diplopia by its very nature is almost always sudden. Aniseikonia, a condition caused by notable discrepancy of the refractive errors between two eyes, gives rise to diplopia because one image is smaller than the other and superimposed. Pronounced image tilting (90° or 180°) may be seen in lateral medullary syndrome. Oblique separation with one image slightly tilted is indicative of either superior or inferior oblique muscle dysfunction. Horizontal diplopia that occurs almost exclusively at near distance is strongly suggestive of convergence insufficiency. For example, left trochlear nerve palsy causes most image separation on right and downward gaze. The images are maximally separated when the direction of gaze is in the region of action of the paretic muscle. The direction of gaze that increases the separation of the images can be helpful in determining which extraocular muscle is involved.
Horizontal diplopia, without vertical separation, is related to the impaired neural control or function of the medial rectus muscle, the lateral rectus muscle, or both. Questions should be asked to identify if the diplopia is horizontal, vertical, or oblique. Alignment of the images and the direction that results in the most separation This group of patients may also describe palinopsia-multiple images appearing in the visual scene soon after gaze has been turned away from an object or after it has been removed from view. Rarely, monocular diplopia may be seen in disorders of the primary or secondary visual cortex, especially when they are bilateral or the patient sees more than two images (cerebral polyopia).
Patients with macular disease causing monocular diplopia may also describe “bent” or “warped” images. For example, a combination of glare and impaired visual acuity can be seen in monocular diplopia caused by cataract. The characteristics of the images may help to localise the problem. Monocular diplopia is usually caused by intraocular pathology, therefore detailed ophthalmological assessment is required. It is very important to distinguish monocular from binocular diplopia because their possible causes differ significantly.
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