A cataract is the clouding of the eye’s natural lens, which is normally a clear structure positioned behind the iris. The lens is responsible for focusing light onto the retina, and when proteins within it begin to clump together, vision becomes progressively impaired. This clouding significantly interferes with the passage of light, leading to various visual disturbances. Cataracts cause double vision, medically known as diplopia, which is one of the many symptoms that can signal the development of a cataract.
The Mechanism of Cataract-Induced Double Vision
The specific type of double vision caused by a cataract is known as monocular diplopia. This means the double image is seen only in the affected eye and persists even when the unaffected eye is closed. This is distinct from binocular diplopia, which is typically caused by issues with eye muscle alignment or neurological problems, and which disappears when either eye is covered.
The mechanism behind monocular diplopia is the irregular density of the clouded lens. As the cataract forms, the lens is no longer uniformly transparent, causing light rays to scatter as they pass through the varying densities of the lens material. Instead of a single, focused point of light hitting the retina, the scattered rays create two or more separate, incomplete images.
The severity of this duplication, sometimes described as “ghosting,” can change depending on lighting conditions. In bright light, the pupil constricts, forcing light through the most central and often most affected part of the cataract, which can sometimes worsen the double vision. As the cataract matures and the entire lens becomes more uniformly opaque, the light transmission may become so poor that the double vision symptom actually diminishes or disappears, replaced by severe overall blurriness.
Recognizing Other Common Cataract Symptoms
While double vision is a notable symptom, cataracts present with a range of other common visual changes that progress slowly over time. One of the most frequently reported symptoms is clouded, blurred, or dim vision, making the world appear as if one is looking through a foggy or frosted window. This haziness cannot be corrected with a change in eyeglasses or contact lenses.
Many people with cataracts experience increased sensitivity to light and glare, a condition known as photophobia. This is often accompanied by seeing halos or glowing rings around light sources, such as streetlights or car headlights, which can make driving at night particularly difficult. The irregular light scattering within the cloudy lens causes this visual disturbance.
The progressive buildup of protein clumps can also cause colors to appear faded, less vibrant, or yellowish. A common sign is the need for frequent changes in an eyeglass or contact lens prescription, as the lens’s increasing opacity continually alters the eye’s refractive power. For some, especially those with a nuclear cataract, vision may temporarily improve in what is sometimes called “second sight,” before vision deteriorates again.
Correcting Vision Loss Caused by Cataracts
The definitive and most effective treatment for vision loss, including double vision, caused by cataracts is surgery. This procedure involves removing the clouded natural lens and replacing it with an artificial lens. The most common surgical technique used today is phacoemulsification, which is a minimally invasive procedure.
During phacoemulsification, a tiny incision is made in the cornea. A small probe is inserted through this incision, which uses high-frequency ultrasonic energy to break the cataract into small pieces. These fragmented pieces are then suctioned out of the eye.
Once the clouded material is removed, a permanent, clear artificial component called an Intraocular Lens (IOL) is inserted into the empty lens capsule. Modern IOLs are designed to restore clear vision and can often correct pre-existing refractive errors, eliminating the blurriness and double vision caused by the original cataract. The small incision is often self-sealing and rarely requires stitches, leading to a relatively quick recovery time. The procedure is performed under local or topical anesthesia.