Double vision, or diplopia, is the perception of two images from a single object, which may appear side-by-side, stacked vertically, or diagonally. LASIK (Laser-Assisted In Situ Keratomileusis) corrects common refractive errors like nearsightedness, farsightedness, and astigmatism. The surgery uses an excimer laser to precisely reshape the cornea, the clear front surface of the eye, improving how light focuses onto the retina. While LASIK is highly effective for correcting blur caused by an improperly shaped cornea, its ability to correct double vision is limited because diplopia often stems from issues unrelated to simple focus.
When LASIK Might Correct Double Vision
LASIK can occasionally be an appropriate treatment, but only for a specific type of double vision called monocular diplopia. Monocular diplopia is defined as double vision that persists even when the unaffected eye is covered. This type of double vision typically originates from an optical imperfection within the affected eye itself, rather than an issue with eye alignment or brain signals.
The most common causes of monocular diplopia that LASIK can address are related to the corneal surface. Severe, uncorrected astigmatism can cause light to scatter and create a ghost image. LASIK works by smoothing and reshaping the corneal tissue to correct this irregularity, allowing light to focus at a single point on the retina. Other corneal irregularities, sometimes resulting from prior trauma or disease, can also be treated if the condition is mild enough for the laser to safely reshape the surface.
Why LASIK Fails to Treat Most Double Vision Cases
LASIK cannot correct the vast majority of double vision because most cases are classified as binocular diplopia. Binocular diplopia is characterized by double vision that immediately disappears when either eye is covered. This indicates the problem is not within one eye’s optical components, but rather a failure of both eyes to point at the same target simultaneously.
This misalignment is typically due to issues with the six extraocular muscles surrounding each eye, or the cranial nerves that control them. Conditions like strabismus, or eye misalignment, are muscular in origin and cannot be treated by reshaping the cornea. LASIK exclusively works on the clear front surface of the eye and has no mechanism to influence the length, tension, or coordination of the muscles that move the eyeball. Neurological disorders, such as those caused by stroke, diabetes, or head trauma, that damage the nerves controlling eye movement are also outside the scope of corneal surgery.
How LASIK Can Induce or Exacerbate Double Vision
While sometimes corrective, LASIK itself carries a risk of inducing double vision as a complication. This most commonly occurs due to the creation of irregular astigmatism, which means the cornea is left with an uneven surface that scatters light. The light scattering effect can cause a ghost image or shadowing, which is a form of monocular diplopia.
Another potential cause is a decentered ablation, where the laser treatment zone is not perfectly centered over the pupil. This can result in light passing through both the treated and untreated parts of the cornea, causing two images to form. Post-operative dry eye syndrome, a common side effect of LASIK, can also temporarily induce monocular diplopia by distorting the tear film. Fortunately, these visual disturbances are often temporary, resolving as the eye heals and dry eye is managed.
Other Effective Treatments for Double Vision
Since binocular diplopia cannot be corrected by LASIK, treatment focuses on restoring eye alignment or compensating for the misaligned images. Prism correction, achieved by incorporating specialized lenses into glasses, is a common non-surgical solution. These prisms bend the light entering the eye, shifting the duplicated image onto the retina so the brain can fuse the two images into a single perception. Fresnel prisms are temporary, press-on versions that can be applied to existing glasses while the eye deviation is still changing.
For issues involving eye muscle weakness or poor coordination, vision therapy offers a structured program of eye exercises. These exercises are designed to improve the communication between the eyes and the brain, enhancing the ability to coordinate movement and maintain single vision. In cases of severe or stable misalignment, strabismus surgery may be necessary to physically adjust the length and position of the eye muscles. As a temporary measure, a simple eye patch or an occlusive contact lens can be used to block the vision in one eye, immediately relieving the double vision symptom.