The two eyes often require different prescriptions. Swapping these lenses, even accidentally, introduces an incorrect optical power to one or both eyes, immediately compromising vision. This common mix-up is easily correctable, but recognizing the problem quickly is the first step toward restoring clear sight and comfort. Prescriptions can vary not just in sphere power (for nearsightedness or farsightedness) but also in base curve and measurements for astigmatism.
Identifying the Symptoms of a Mismatch
The most immediate and noticeable sign of a lens swap is the sudden onset of blurred or distorted vision, even though the lenses feel correctly placed on the eye. The severity of this visual impairment depends directly on the difference in prescription between the two eyes. If the sphere powers, which correct for long or short-sightedness, are vastly different, the vision will be significantly out of focus.
Individuals with astigmatism, who require toric lenses, may experience a more pronounced and complex blur, often accompanied by visual instability. Toric lenses correct for the eye’s irregular, football-like curvature by having additional optical power applied at a specific angle, known as the axis. A swapped toric lens not only provides the wrong power but also positions the correction at an incorrect angle, which can lead to uncomfortable visual symptoms. This optical strain can quickly manifest in physical symptoms like eye fatigue, headache, and even dizziness or mild nausea.
The physical fit of the lens might also be compromised. Contact lenses are designed to fit the specific curvature of each eye, known as the base curve, which can vary between the left and right eye. While wearing an incorrect lens for a short time may not cause damage, the ill-fitting lens may feel uncomfortable or gritty. This discomfort may cause the lens to move excessively on the eye’s surface or even pop out more easily.
Verifying Lens Placement
If you suspect a swap has occurred based on immediate discomfort or visual symptoms, the next step is to objectively confirm the placement. You should first remove both lenses and place them into clean, separate containers of fresh solution to prevent any further mix-up. The only way to definitively verify a swap is to check the optical specifications of the lenses against your written prescription.
Your prescription details are typically printed on the side of the original contact lens box or on the foil lid of the individual blister packs. These specifications list the power, base curve (BC), and diameter (DIA) for both the right eye (OD) and the left eye (OS). For those with astigmatism, the cylinder (CYL) and axis (AX) will also be included, and these values are especially likely to differ between the two eyes.
Verification involves comparing the prescription information on the blister pack of an unopened lens to the lens currently stored in the corresponding contact lens case compartment. For example, if the lens in the ‘R’ compartment of your case matches the prescription for your ‘L’ eye blister pack, the lenses are confirmed to be swapped. If the lenses are already in your eyes and you cannot check the cases, remove them and perform a quick vision check by trying each lens individually in the eye you know is worse. The lens that provides the best correction in the eye with the higher dioptric power is the correct lens for that eye.
Immediate Corrective Action
Once a lens swap is confirmed, immediate corrective action must be taken to restore clear vision and comfort. The first step is to wash your hands thoroughly with soap and water before handling the lenses to reduce the transfer of germs. This hand hygiene is non-negotiable before touching the lenses or the eye surface.
Remove both lenses from your eyes and place them in the palm of your hand with a few drops of fresh contact lens solution. Even though the lenses were only recently inserted, rub them gently for several seconds to clean the surfaces before re-insertion. Next, rinse both lenses thoroughly with the contact lens solution, ensuring all traces of debris or solution from the eye are removed.
You must then carefully identify the correct lens for each eye based on your verification, using the prescription information you found on the packaging or case. Reinsert the correct lens into the proper eye, always ensuring the lens is not inside-out, which would cause discomfort and movement. Finally, empty the old solution from your contact lens case and refill both compartments completely with fresh solution before storing the lenses again.
Preventing Future Swaps
Preventing future mix-ups relies on establishing a consistent and mindful routine for handling your lenses. Always handle one eye first, starting and finishing the process with the same eye every time. For instance, commit to always removing the right lens first and placing it directly into the right compartment of the case before touching the left lens.
When inserting lenses, always remove the right lens from the case first and place it in the right eye before proceeding to the left. This consistent sequence reduces the opportunity for a momentary lapse in attention to result in a swap. Ensure your contact lens case is clearly marked or even color-coded for the right and left sides to minimize visual confusion. Regularly replacing the contact lens case, at least every three months, is important for maintaining eye health, as bacteria can build up over time.