Monocular Diplopia and Ghost Images: Causes, the Pinhole Test and How to Find the Source
Last updated: November 2026
Double vision that persists when the other eye is covered is monocular diplopia. It is almost always an optical problem of the tear film, cornea, lens or IOL, not a nerve or muscle problem, so it rarely needs neuroimaging. A few minutes with a pinhole, a retinoscope and a slit lamp usually finds the cause.
Confirm it is monocular
- Cover each eye in turn: monocular diplopia persists with the other eye covered; binocular diplopia disappears when either eye is covered (see diplopia approach).
- It may be in both eyes separately (bilateral monocular diplopia), common with astigmatism, dry eye or cataract.
- Patients often describe a ghost or shadow next to letters rather than two clear images.
The pinhole test
| Pinhole result | Meaning |
|---|---|
| Double image disappears | Optical cause: refractive error, tear film, cornea, lens or IOL |
| Double image persists | Macular cause (epiretinal membrane, macular oedema, choroidal folds) or, rarely, cerebral polyopia |
Causes
| Site | Causes | Clues and tests |
|---|---|---|
| Refraction | Uncorrected or undercorrected astigmatism; wrong axis | Refraction; ghosting along one meridian |
| Tear film | Dry eye, meibomian gland dysfunction | Ghosting improves after blinking or drops; tear break-up time |
| Cornea | Keratoconus, irregular astigmatism, scars, after refractive surgery, corneal dystrophies, contact lens warpage | Scissors reflex, topography, rigid lens trial improves vision |
| Iris | Polycoria, large peripheral iridectomy or iridotomy, iris defects | Slit lamp, retro-illumination |
| Lens | Early cataract (cortical spokes, oil-droplet nucleus, water clefts), lens subluxation | Red reflex and retro-illumination |
| IOL | Decentration, tilt, edge effects, toric misalignment, PCO, capsular folds | Dilated slit lamp examination |
| Macula | Epiretinal membrane, macular oedema, central serous chorioretinopathy | Amsler grid, OCT; pinhole does not help |
| Brain (rare) | Cerebral polyopia (occipital lesions); usually both eyes and with other signs | Fields, neurological review |
Management
| Cause | Management |
|---|---|
| Astigmatism | Full cylindrical correction; toric contact lens |
| Dry eye | Lubricants, lid hygiene, treat MGD |
| Irregular cornea | Rigid gas permeable or scleral lens; cross-linking for progressive keratoconus |
| Cataract | Cataract surgery when symptoms affect daily life |
| IOL problems | Repositioning, toric rotation, Nd:YAG for PCO, exchange |
| Iris defects | Tinted or opaque contact lens, iris repair |
Pearls
- Cover the other eye first: this one step separates monocular from binocular diplopia.
- If the pinhole fixes it, look at the tear film, cornea and lens.
- A rigid contact lens over-refraction that clears the ghosting proves a corneal cause.
Common mistakes
- Ordering an MRI for monocular diplopia that resolves with pinhole.
- Missing dry eye because the patient blinks just before reading.
- Overlooking an epiretinal membrane when the pinhole does not help.
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Related: Approach to Diplopia: Monocular vs Binocular and the Three-Step Test, Keratoconus: Signs, Indices, Staging, Progression and Treatment, Night Myopia, Pseudomyopia and Other Myopic Shifts: When "More Minus" Is Not True Myopia, Positive vs Negative Dysphotopsia After Cataract Surgery, TFOS DEWS III: What Changed in Dry Eye Diagnosis and Treatment.
Key sources
- Coffeen P, Guyton DL. Monocular diplopia accompanying ordinary refractive errors. Am J Ophthalmol. 1988;105:451-459
- Morris RJ. Double vision as a presenting symptom in an ophthalmic casualty department. Eye. 1991;5:124-129
- Miller NR, Newman NJ. Walsh and Hoyt's Clinical Neuro-Ophthalmology. Monocular diplopia and polyopia
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