What causes double vision in one eye and how is it treated?

Double Vision in One Eye: Causes and Treatment

Monocular diplopia (double vision in one eye) is almost always caused by optical problems within the affected eye itself—most commonly refractive errors, cataracts, or retinal disease—and requires ophthalmologic evaluation and treatment of the underlying ocular pathology. 1

Distinguishing Monocular from Binocular Diplopia

The critical first step is determining whether diplopia is monocular or binocular by having the patient cover each eye separately 2, 1:

• Monocular diplopia: Double vision persists when only the affected eye is open and resolves when that eye is covered 1
• Binocular diplopia: Double vision resolves when either eye is covered, indicating ocular misalignment 2, 1

This distinction fundamentally changes the diagnostic approach and treatment, as monocular diplopia originates from intraocular pathology rather than extraocular muscle or neurological problems 1.

Common Causes of Monocular Diplopia

Optical and Refractive Causes

• Refractive errors (uncorrected astigmatism, irregular astigmatism) 1
• Cataracts causing light scatter and image distortion 1
• Corneal irregularities (keratoconus, corneal scarring, dry eye) 1
• Lens subluxation or dislocation 1

Retinal Causes

• Macular disease including epiretinal membranes, which affect 2% of people under 60 and 12% over age 70 3
• Binocular central diplopia (dragged-fovea syndrome): 16-37% of patients with epiretinal membranes or maculopathy develop this condition where distorted macular images create perceived double vision even with proper eye alignment 3, 4

Important caveat: Binocular central diplopia is technically binocular but presents with features that may confuse the initial assessment, as patients have retinal image distortion rather than true ocular misalignment 4.

Diagnostic Approach for Monocular Diplopia

Initial Ophthalmologic Examination

• Refraction to identify and correct refractive errors 1
• Slit-lamp examination to evaluate cornea, lens, and anterior segment 1
• Dilated fundus examination to assess retinal pathology 5
• Amsler grid testing to detect metamorphopsia and macular distortion 4, 3

Specialized Testing for Retinal Diplopia

When maculopathy is suspected:

• Awaya test to quantify aniseikonia (unequal image sizes) 4, 3
• Lights on/off test (pathognomonic for dragged-fovea syndrome): In complete darkness, central fusion allows single vision; when lights turn on, peripheral fusion causes diplopia to resume 4
• Optotype-frame test: Alternative when complete darkness cannot be achieved—patient fixates on isolated letter and reports whether the letter versus monitor frame appears single or double 4

Treatment Strategies

For Optical/Refractive Monocular Diplopia

Treatment targets the underlying ocular pathology 1:

• Refractive correction with glasses or contact lenses for refractive errors 1
• Cataract surgery when lens opacity is the primary cause 1
• Corneal treatment (lubrication for dry eye, rigid gas permeable lenses for irregular astigmatism) 1

For Binocular Central Diplopia (Retinal Origin)

Fogging one eye is the most successful long-term treatment for binocular central diplopia, as it eliminates the foveal conflict by creating a central scotoma 4:

Non-Surgical Options (First-Line)

• Observation/monitoring if symptoms are mild or occasional 4
• Fogging techniques (in order of patient tolerance):
  • Bangerter foils (best tolerated) 4
  • Scotch Satin tape 4
  • Occlusive contact lenses 4
  • Combination: Small prism plus Bangerter foil may provide better relief in difficult cases 4

Critical limitation: Prism correction alone is rarely curative because it doesn't resolve the mismatch of distorted macular images, though it may transiently reduce symptoms in some patients 4

Surgical Options (Selected Cases Only)

• Epiretinal membrane peeling: May be effective in some patients but carries risk of inducing new diplopia in previously non-diplopic patients 4
• Strabismus surgery: Only consider if synoptophore testing demonstrates that superimposition of foveal images reduces diplopia AND symptoms are incompletely addressed by fogging/optical correction 4

Important warning: Patients should be counseled that binocular central diplopia usually does not improve spontaneously and may worsen over time 4

Referral Patterns

• Monocular diplopia from optical causes: Refer to comprehensive ophthalmologist or optometrist 1
• Suspected retinal pathology: Refer to retina specialist 4
• Binocular central diplopia: Coordinate care between retina specialist and strabismus specialist (pediatric ophthalmologist, orthoptist, or neuro-ophthalmologist) 4

Rare Cortical Causes

Cerebral polyopia (multiple images) and palinopsia (visual perseveration) are extremely rare forms of monocular diplopia arising from occipital lobe dysfunction, often associated with migraine or structural lesions 1. These require neurologic evaluation and neuroimaging 1.

Common Pitfalls to Avoid

• Assuming all "double vision" is true diplopia: Many patients use "double vision" to describe blurred vision or visual distortion rather than true image separation 6
• Missing binocular central diplopia: This condition may be mistaken for simple strabismus, but treating the small-angle deviation surgically without addressing the retinal distortion will fail 4
• Overlooking treatable causes: Some patients with retinal misregistration have coexisting treatable strabismus that should not be ignored 4