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Combination of images from each eye into a single image (fusion) requires intact, bilaterally coordinated extraocular movements. Diplopia, or double vision, may be monocular or binocular. Monocular diplopia is present with only one eye open; binocular diplopia disappears when either eye is closed. Causes of monocular diplopia include cataract, refractive error (most often astigmatism), corneal scarring, dislocated lens, keratoconus, and retinal detachment. Binocular diplopia almost always suggests dysconjugate alignment of the eyes. Causes of intermittent binocular diplopia include myasthenia gravis and latent eye deviation (phoria) that becomes uncompensated. Causes of constant binocular diplopia include palsy of the 3rd, 4th, or 6th cranial nerves; orbital disease (eg, thyroid eye disease, tumor, pseudotumor); or CNS abnormalities (vertebrobasilar insufficiency, internuclear ophthalmoplegia).
History should determine if diplopia involves one or both eyes intermittently or constantly and if the images are separated vertically, horizontally, or a combination of both. Diplopia must also be distinguished from blurriness.
Vision in each eye should be checked with the other eye covered to determine if the diplopia is monocular or binocular. Examination should note presence of eyelid droop, pupillary abnormalities, or dysconjugate eye movement during extraocular muscle testing.
Ocular motility is checked by having the patient hold his head steady and having the patient track the examiner's finger, which is moved to extreme gaze to the right, left, upward, downward, diagonally to either side, and finally inward toward the patient's nose. Mild paresis of ocular motility sufficient to cause diplopia may escape detection by such examination. If diplopia occurs in one direction of gaze, the eye that produces each image can be determined by repeating the examination with a red glass placed over one of the patient's eyes. The image that is more peripheral originates in the paretic eye; eg, if the more peripheral image is red, the red glass is covering the paretic eye. If a red glass is not available, the paretic eye can sometimes be identified by having the patient close each eye; the eye that, when closed, eliminates the more peripheral image, is paretic. If the paretic eye is recognized but it is unclear whether the eye is esotropic (crossed in) or exotropic (crossed out), a red glass can be placed in front of the paretic eye. If the paretic eye is esotropic, the red light appears to the right of the white light. If the paretic eye is exotropic, the red light appears to the left of the white light.
Specific maneuvers (eg Park's 3-step, which compares eye alignment in different positions; the Hess screen and Lancaster red-green tests, which assess patient responses to dissimilar images produced by special glasses; and double Maddox rod testing, which assesses degree of rotation of striated lenses necessary to make lens lines appear parallel) can be performed to identify the involved muscle(s) and/or cranial nerve(s).
Follow-up testing may include corneal topography (measurement of corneal shape) to identify keratoconus; phorometry (testing of ocular muscle balance) to detect phoria; exophthalmometry (measurement of the amount of protrusion of the eyeball) to measure exophthalmos; CT or MRI to detect orbital disease or CNS abnormalities; and blood testing for thyroid dysfunction and diabetes, which underlie some cranial nerve palsies.
Treatment is management of the underlying cause.
Last full review/revision November 2005
Content last modified November 2005
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