Double vision is the simultaneous perception of two images from a single object. It affects balance, reading, and the ability to perform daily tasks like driving. Correction depends entirely on accurately identifying the underlying cause, making a professional eye exam the first step. Diplopia is categorized into two types: monocular and binocular. Monocular double vision persists when the unaffected eye is covered, often appearing as a ghost image or shadow. Binocular double vision disappears instantly when either eye is closed, indicating a problem with the two eyes working together. Monocular diplopia usually points to an issue within the eye structure itself, while binocular diplopia suggests misalignment or a problem with the nerves or muscles controlling eye movement.
Identifying the Source of Double Vision
Correction begins with a comprehensive eye examination to pinpoint the source of the double vision. The eye doctor determines the type of diplopia using a simple test: asking the patient to cover one eye. If the double image resolves, the condition is binocular, suggesting eye misalignment; if it persists, it is monocular, pointing toward a structural eye issue.
For binocular double vision, the practitioner performs specialized cover and motility tests to evaluate eye movement and coordination. The cover/uncover test assesses eye deviation, while the prism and alternate cover test measures the degree of misalignment. Monocular diplopia is often related to issues like astigmatism, dry eyes, or cataracts, which are diagnosable through a standard physical eye exam. Binocular cases may require further investigation, such as magnetic resonance imaging (MRI) or computed tomography (CT) scans, to rule out neurological causes affecting the cranial nerves or brain.
Prism Lenses and Other Optical Aids
Prism lenses manage stable binocular double vision by optically fusing the two images. These lenses are designed with a wedge shape that bends light before it enters the eye, compensating for the visual offset caused by eye misalignment. The prism redirects the light so the image falls on the corresponding part of the retina in each eye, allowing the brain to perceive a single picture. This correction occurs without demanding the eye muscles to correct the underlying misalignment.
Correction is measured in prism diopters, and the prescription specifies both the power and the direction, or “base,” of the prism. Temporary press-on Fresnel prisms can be applied to existing eyeglasses to trial the correction or when misalignment is changing. The prism can also be ground directly into the eyeglass lens, often split between both lenses to reduce thickness and improve appearance. When double vision is severe or unstable, temporary solutions like an eye patch or an occlusive lens (which blocks vision in one eye) may provide immediate relief.
Vision Therapy and Eye Exercises
Vision therapy is a structured, doctor-supervised program designed to retrain the eyes and brain to work together. This method aims to improve coordination, focusing, and tracking abilities, addressing the root of some binocular vision problems. Unlike passive optical aids, therapy seeks to build new, long-lasting visual skills that can resolve the coordination problem over time.
A common technique involves convergence exercises, such as the “pencil push-up,” where a person focuses on a near object and slowly brings it closer to the nose to train the eyes to turn inward. Other activities may use specialized stereograms or computer programs to enhance binocular function. The exercises focus on strengthening the neurological control center for the eye muscles, leveraging the brain’s ability to adapt. Consistent practice, often involving a combination of in-office sessions and at-home routines, is necessary to achieve lasting single vision.
Addressing Underlying Physical Causes
When optical correction and vision therapy are insufficient, treatment must target the structural or systemic origin of the diplopia. For misaligned eyes (strabismus), surgery on the extraocular muscles may be necessary. This procedure involves adjusting the length or attachment point of one or more muscles to realign the eyes, allowing them to focus together. Strabismus surgery is a highly effective outpatient procedure, with a significant majority of patients achieving satisfactory alignment with a single operation.
For monocular double vision, correction involves treating the physical cause, such as removing a cloudy lens through cataract surgery. Many cases of binocular diplopia are symptoms of systemic diseases, necessitating coordinated care with other medical specialists. For example, double vision caused by Graves’ disease or diabetes requires medication and management of the underlying condition. In some cases, botulinum toxin (Botox) injections can be used to temporarily weaken an overactive eye muscle, providing an alternative to surgery or a diagnostic tool to assess the potential outcome of a permanent procedure.