What is the diagnosis and treatment approach for a patient with monocular diplopia (double vision in one eye)?

Diagnosis and Treatment of Monocular Diplopia

Monocular diplopia is most commonly caused by refractive errors, corneal irregularities, lens abnormalities, or retinal issues, and treatment should be directed at the specific underlying cause after a thorough ophthalmologic examination. 1

Diagnostic Approach

Initial Evaluation

• Confirm that diplopia is truly monocular by having the patient cover each eye alternately
  • If double vision persists with one eye covered, it's monocular diplopia
  • If double vision resolves with either eye covered, it's binocular diplopia

Key Diagnostic Tests

1. Visual acuity and refraction assessment (essential first step)
2. Pupillary examination
3. Slit-lamp biomicroscopy to examine:
   • Corneal irregularities (scars, keratoconus)
   • Lens abnormalities (cataracts, subluxation)
   • Iris abnormalities
4. Dilated fundus examination to assess retinal causes
5. Amsler grid testing for metamorphopsia 2

Classification of Monocular Diplopia

Based on etiology, monocular diplopia can be classified as 3:

1. Refractive - due to uncorrected refractive errors
2. Aberration - from optical aberrations in the eye
3. Pupillary - related to pupil abnormalities
4. Retinal - from retinal disorders
5. Neurogenic - central nervous system causes

Treatment Approach

Refractive Causes

• Correct refractive errors with appropriate glasses or contact lenses
• Consider pinhole testing - improvement with pinhole suggests refractive cause
• Address astigmatism which is a common cause

Corneal Causes

• Treat dry eye with artificial tears, punctal plugs, or other therapies
• Manage keratoconus with rigid gas permeable contact lenses or consider corneal crosslinking
• Evaluate corneal scars - may require surgical intervention if severe

Lens Abnormalities

• Cataract extraction for lens opacities causing significant visual symptoms
• Address lens subluxation surgically if causing significant symptoms

Retinal Causes

• Treat underlying retinal conditions (epiretinal membrane, macular edema)
• Consider vitrectomy for severe epiretinal membranes causing significant visual distortion

Neurogenic Causes

• Neuroimaging may be warranted if no ocular cause is found
• Treat underlying neurological conditions if identified

Temporary Measures

• Pinhole glasses can temporarily improve monocular diplopia of refractive origin
• Occlusion therapy for intractable monocular diplopia when other treatments fail 2

Important Considerations

Pitfalls to Avoid

• Don't confuse with binocular diplopia - ensure proper diagnosis by covering one eye
• Don't miss subtle corneal irregularities - use corneal topography when available
• Don't overlook psychogenic causes - consider this when no organic cause is found despite thorough evaluation
• Don't neglect to rule out serious neurological causes when no ocular cause is identified

Prognosis

• Prognosis depends on the underlying cause:
  • Refractive causes typically have excellent outcomes with proper correction
  • Corneal and lens causes generally respond well to appropriate interventions
  • Retinal causes may be more challenging to resolve completely 2

Follow-up

• Regular follow-up is essential to monitor response to treatment
• Persistent unexplained monocular diplopia warrants referral to a neuro-ophthalmologist

Monocular diplopia should be managed by an ophthalmologist with expertise in diagnosing and treating ocular abnormalities, with referral to subspecialists (cornea, retina, neuro-ophthalmology) as needed based on the suspected etiology 1.