The practice of wearing a contact lens in only one eye, known as unilateral correction, often occurs unintentionally when a lens is lost or damaged, leaving one eye corrected and the other uncorrected. This introduces a significant imbalance in the visual system, forcing the brain to process two highly disparate images—one clear and one blurry—which creates immediate visual stress. Except for specific, medically prescribed reasons, this situation is not a recommended method for standard vision correction and can lead to acute discomfort and functional impairment.
Immediate Symptoms of Uneven Correction
The most immediate consequence of correcting only one eye is physical strain as the brain attempts to reconcile the two different inputs. This disparity forces the eyes’ internal focusing mechanisms to work overtime, a condition called accommodative strain. The ciliary muscles, which change the shape of the eye’s lens to maintain focus, experience fatigue and soreness around the eyes.
This imbalance also affects the external eye muscles responsible for aligning the eyes, known as the vergence system. To prevent double vision, the brain must exert extra effort to maintain proper alignment, which can manifest as a muscle imbalance called phoria. This increased muscular effort contributes directly to generalized eye strain, or asthenopia, which is characterized by symptoms like a heavy sensation in the eyelids or a persistent ache behind the eyes.
As the day progresses, this continuous effort often results in tension headaches or migraines, a direct result of the visual system’s struggle to find a stable focus. The visual confusion can also trigger systemic symptoms, such as dizziness or mild nausea, because the brain receives conflicting signals about the environment’s stability. The uncorrected eye’s blurry input compels the corrected eye to work harder, creating a cycle of fatigue that quickly compromises visual comfort.
Impact on Depth Perception and Binocular Function
Wearing only one contact lens severely compromises the ability of the two eyes to work together, a process known as binocular fusion. Stereopsis relies on the brain receiving two nearly identical images that it can fuse together. When one eye is corrected and the other is not, the resulting difference in refractive power makes this fusion extremely difficult.
The brain’s natural response to this visual confusion is often to suppress the image from the blurrier, uncorrected eye. This suppression mechanism prevents the perception of double vision, but it comes at the cost of losing stereoscopic vision. With the brain effectively ignoring the input from one eye, the ability to accurately judge the relative distance of objects is significantly impaired.
While short-term unilateral wear typically does not cause permanent damage in adults, the brain’s tendency to suppress the weaker image is a concern if this practice is maintained for an extended period. In children, prolonged suppression due to uncorrected, uneven vision can lead to the development of amblyopia, commonly known as a lazy eye. For adults, the immediate loss of reliable depth perception creates safety hazards.
Specific Scenarios and Safety Recommendations
Given the immediate strain and loss of depth perception, wearing only one contact lens should be avoided, particularly during activities that require precise judgment and focus. This includes driving, operating heavy machinery, or engaging in sports. The compromised ability to judge speed and distance poses a risk to safety.
If a lens is lost or damaged, the best temporary solution is to remove the remaining contact lens and switch to backup glasses until the missing lens can be replaced. If glasses are unavailable, removing the single lens ensures that both eyes are equally uncorrected. This temporary fix should only last for a few hours.
Monovision is the only intentional, medically sanctioned scenario for unequal correction, often used to manage presbyopia, or age-related near vision loss. In a monovision prescription, one contact lens corrects for distance vision, and the other is set for near vision. This is a highly specialized correction that requires a period of adaptation and professional fitting by an eye care specialist. Any decision to adopt unequal correction should only be made after consultation with an optometrist or ophthalmologist.