Wearing two contact lenses in the same eye, whether accidentally or intentionally, is generally unsafe and strongly discouraged by eye care professionals. A single contact lens is precisely calculated based on specific measurements of oxygen permeability and corneal curvature. Doubling the lenses, or “stacking,” immediately compromises the intended physiological and optical fit, posing a genuine threat to the delicate structures of the eye. This practice should be avoided, with rare exceptions occurring only under the direct supervision of an eye doctor.
Immediate Physical Risks of Wearing Two Lenses
The most immediate danger posed by wearing two contact lenses is a severe reduction in the oxygen that reaches the cornea, a condition known as hypoxia. The cornea receives nearly all of its oxygen directly from the air, and a single lens is already engineered to maximize this flow. Stacking a second lens dramatically lowers the overall oxygen transmission rate (Dk/t value), effectively suffocating the corneal tissue.
This oxygen deprivation can rapidly lead to corneal edema, which is a swelling of the cornea, causing blurred vision and discomfort. A hypoxic environment also increases the risk of serious eye infections, such as a corneal ulcer. These ulcers are painful, develop quickly, and may result in permanent vision loss if not treated promptly.
Stacked lenses distort the intended fit and movement on the eye’s surface. The combined thickness causes excessive friction against the inner eyelid and the cornea, leading to mechanical irritation, redness, and a scratchy sensation. Improper fit can also cause the lenses to seal too tightly, potentially trapping debris and bacteria between the layers.
Optically, layering two lenses, even identical ones, results in poor visual acuity. The prescriptions are additive, meaning the combined power will be incorrect, leading to significant blurring or double vision. The misalignment of two curved surfaces further compounds the optical distortion.
How to Check for a Doubled Lens and Remove It Safely
Accidentally doubling a lens is common, especially with thin daily disposable lenses that stick together easily. A primary indicator that two lenses are present is an immediate feeling of intense discomfort or the sudden onset of highly blurred vision shortly after insertion. The eye may feel noticeably irritated, and the stacked lenses may feel thicker or more rigid on the eye than a single lens.
If a doubled lens is suspected, first wash and thoroughly dry hands with a non-lotion soap to prevent introducing contaminants. If the lens feels stuck or dry, apply a few drops of sterile saline or contact lens rewetting drops to lubricate the eye and loosen the stack. Never attempt to remove a dry, stuck lens without first rehydrating it.
To remove the lenses, look upward and use the middle finger to pull down the lower eyelid. Gently use the index finger pad to slide the contact lens stack down onto the white part of the eye, away from the sensitive cornea. Once the lens is on the white of the eye, gently pinch it off using the pads of the thumb and index finger.
After removal, separate the lenses carefully to confirm two were present, and rest the eye before inserting a fresh, single lens. If significant redness, pain, or blurred vision persists, consult an eye care professional immediately.
When Dual Lenses Are Used Under Medical Supervision
Rare, specialized circumstances exist where an eye care professional may prescribe two lenses on the same eye, but never using standard, off-the-shelf corrective lenses.
The Piggyback System
One established method is the “piggyback” system, which involves placing a soft contact lens directly on the cornea and fitting a rigid gas permeable (RGP) lens on top. This is typically used for patients with complex corneal conditions, such as severe keratoconus. The soft lens acts as a comfortable cushion beneath the RGP lens to improve fit and tolerance.
Bandage Lenses
Another medically justified application involves a non-corrective bandage lens. Following a corneal injury, surgery, or to protect a damaged surface, a clear, non-prescription soft lens may be placed over a standard corrective lens or directly on the eye. The bandage lens acts as a protective shield, allowing underlying tissue to repair itself without the friction of blinking. These dual-lens applications require meticulous fitting and frequent monitoring to ensure proper oxygen flow and prevent complications.