The question of whether it is acceptable to wear only one contact lens often arises from a lost lens or an attempt to save money. Wearing a single corrective lens provides unilateral correction, which fundamentally disrupts how the two eyes work together. The visual system relies on both eyes sending coordinated images to the brain (binocular vision), and introducing an uncorrected difference can have significant consequences for visual comfort and function.
Understanding Visual Imbalance
When a person wears a lens in only one eye, it instantly creates a significant difference in refractive power between the two eyes, known as induced anisometropia. The brain receives a clear image from the corrected eye and a blurred image from the uncorrected one. This conflict forces the visual system to work harder to merge these disparate images into a single, cohesive picture.
This extra effort often leads to visual fatigue (asthenopia), which manifests as persistent headaches and eye strain. If the difference in clarity is substantial, the brain may subconsciously begin visual suppression. Suppression means the brain ignores information from the blurrier, uncorrected eye to avoid double vision or confusion.
Prolonged suppression can negatively affect binocular skills and overall visual comfort. While a difference in prescription of up to one diopter is often tolerated without symptoms, a greater disparity strains the ocular muscles and the brain’s processing centers. The resulting discomfort is a direct result of the brain struggling to reconcile the two uneven visual inputs.
Monovision and Prescribed Single Lens Use
Wearing a single contact lens is sometimes an intentional and medically recommended course of action. The most common example is monovision, a strategy used to address presbyopia (the age-related loss of near focusing ability). In a monovision plan, one contact lens provides clear distance vision, and the other eye is corrected for clear near vision.
This approach requires an adaptation period as the brain learns to favor the distance-corrected eye for far objects and the near-corrected eye for reading. Monovision is a compromise designed to reduce dependence on reading glasses, and it is closely monitored by an eye care professional. The system relies on the brain’s plasticity to integrate the two differently focused images.
A single lens may also be prescribed in cases where a person only needs correction in one eye, a condition called simple anisometropia. This occurs with unilateral myopia or hyperopia, or following eye surgeries where one eye has been fully corrected. In these instances, the single-lens wear is part of a complete vision plan tailored to the patient’s refractive needs.
Practical Concerns and Safety Implications
One significant functional compromise from unilateral correction is the loss of stereopsis, or depth perception. Depth perception relies on the brain comparing the slightly different images received by each eye. When one image is blurred, the brain cannot accurately calculate distance, which impairs everyday activities requiring precise spatial judgment.
Tasks such as driving, especially judging distance to other vehicles, can become more hazardous. Navigating stairs, catching a ball, or working with tools can also be complicated by diminished depth perception. For high-stakes activities, maintaining clear, balanced vision in both eyes is paramount.
Many jurisdictions have minimum visual acuity standards for driving, which rely on the combined visual function of both eyes. The visual compromise from wearing a single lens may prevent a person from meeting these standards, particularly at night. Monovision wearers often report increased difficulty with glare and reduced visual acuity in low-light conditions.
When to Consult an Eye Care Professional
If a lens is lost or damaged, the safest immediate course of action is to switch to glasses until a replacement arrives. This prevents the immediate onset of visual imbalance and associated symptoms. Relying on a single lens for an extended period should only be done under the supervision of an eye care professional.
Anyone considering wearing only one contact lens, or experiencing symptoms like headaches or eye strain, should schedule a comprehensive eye examination. Only a doctor can accurately assess the prescription difference and determine if unilateral correction is safe and appropriate for the person’s visual needs and lifestyle. Self-prescribing an uneven correction may lead to discomfort and potentially compromise visual function.