Diplopia

The perception of two images of a single object. Monocular diplopia persists with one eye covered and arises from optical problems within the eye; binocular diplopia disappears when either eye is covered and indicates misalignment of the visual axes.

• Monocular causes: cataract (including early nuclear and posterior subcapsular), corneal irregularity (keratoconus, scars, dry eye), refractive error, uncorrected astigmatism, pupil abnormalities, iridectomy, macular disease (drusen, distortion), intraocular lens decentration, and occasionally cortical causes (palinopsia, polyopia).
• Binocular causes: third, fourth and sixth cranial nerve palsy, myasthenia gravis, thyroid eye disease, orbital fracture with entrapment, orbital inflammation or mass, internuclear ophthalmoplegia, skew deviation, brainstem stroke or tumour, decompensated phoria or congenital palsy, convergence insufficiency, post-cataract or refractive surgery, local anaesthetic myotoxicity, giant cell arteritis, Wernicke, botulism, Guillain-Barre (Miller Fisher), and cavernous sinus disease.

• Horizontal diplopia suggests sixth nerve palsy, medial rectus restriction or convergence disorders; vertical or oblique diplopia suggests fourth nerve, third nerve, skew, thyroid disease or myasthenia.
• Diplopia worse at distance: abducens palsy or divergence insufficiency; worse at near: convergence insufficiency or medial rectus weakness.
• Variable diplopia worse at the end of the day: myasthenia gravis. Pain on eye movement: orbital inflammation, optic neuritis, thyroid disease. Headache, scalp tenderness and jaw claudication: giant cell arteritis.
• Associated neurological signs, headache, ataxia, vertigo, ptosis, pupil changes and facial sensory changes localise the lesion; recent trauma, fever, infection, immunisation or drug exposure.
• Binocular diplopia in a child often leads to suppression or amblyopia instead of double vision.

• Establish monocular versus binocular first by covering each eye, and the pinhole test for monocular diplopia.
• Examination: acuity, refraction, pupils, lid position, cover test in nine positions, prism cover test measurements, ocular motility and versions, convergence near point (normal 6 to 10 cm), red glass test or Maddox rod, Hess or Lees screen, forced duction test, saccadic velocity, head posture, and fundus with torsion assessment.
• Three step test for vertical diplopia; upright supine test for skew deviation.
• Targeted tests: ice pack test and antibodies for myasthenia; thyroid function and orbital imaging for thyroid disease; ESR, CRP and platelets in patients over 50 (giant cell arteritis); glucose, HbA1c, blood pressure, lipids; CT or MR angiography for painful or pupil involving third nerve palsy; MRI brain and orbits with contrast for other neurological signs and any child; CT orbits for trauma; lumbar puncture with imaging for raised intracranial pressure or meningitis.
• Red flags needing same day neuroimaging: pupil involving palsy, headache with papilloedema, new neurological signs, age under 50 without cause, progressive or multiple cranial neuropathy.

• Monocular: correct refraction, treat dry eye, cataract surgery, contact lens fit for irregular cornea, corneal surgery as indicated.
• Binocular: treat the cause (aneurysm repair, steroids and temperature control for giant cell arteritis, thyroid disease treatment, myasthenia therapy, repair of orbital fracture entrapment within 24 to 72 hours in children, otherwise within 2 weeks for adults with persistent entrapment).
• Temporary relief: occlusion with a patch, a frosted lens or an eyelid tape; alternating patches to prevent suppression in children; Fresnel prisms (1 to 30 prism dioptres) while the angle is changing; ground in prisms for stable deviations up to about 10 to 12 prism dioptres.
• Convergence insufficiency: office based vergence therapy (about 12 weeks with home pencil push ups for 15 minutes a day, 5 days a week); base in prism for near; reading glasses adjustments.
• Botulinum toxin (2.5 to 5 units) to the antagonist muscle in acute sixth nerve palsy or thyroid disease with a small deviation.
• Strabismus surgery after 6 months of stable measurements: recession and resection of rectus muscles, adjustable sutures, transposition procedures for palsy; inferior rectus recession for thyroid eye disease.
• Driving advice: stop driving until diplopia is controlled by patching or prisms; counsel on the risk of falls.