Contact lenses are medical devices designed to correct vision by sitting directly on the surface of the eye. They function by gently floating on the tear film, covering the cornea, which is the transparent front part of the eye. Contact lenses are highly personalized items. Sharing them with another person, even briefly, introduces significant risks to eye health and must be avoided under all circumstances.
How Shared Lenses Spread Infection
Sharing a contact lens means transferring the unique collection of microorganisms from one person’s eye and tear film directly to another individual’s cornea. This microbial transfer is a direct route for transmitting various pathogens, including bacteria, viruses, fungi, and parasites. The lens acts as a carrier, or vector, for infectious agents from the first wearer’s eye surface. Over half of worn contact lenses can harbor microorganisms, even in wearers who show no symptoms of infection.
This practice significantly increases the risk of developing microbial keratitis, which is an inflammation of the cornea. Keratitis caused by bacteria, such as Pseudomonas aeruginosa or Staphylococcus aureus, can lead to corneal ulcers and potentially permanent vision loss if not treated immediately. Sharing lenses also risks the transfer of Acanthamoeba, a free-living amoeba found in water and soil. This parasite adheres to the lens surface and causes a rare but often blinding form of keratitis that is difficult to eradicate.
The Danger of an Improper Fit
Contact lenses are precisely fitted medical devices, and their successful function relies on the exact topography of the individual cornea. A contact lens prescription includes specific measurements like the base curve and diameter, which dictate how the lens rests on the eye’s surface. These parameters ensure the lens centers correctly, moves slightly with each blink, and allows adequate oxygen to reach the cornea.
Wearing a lens not specifically fitted for one’s eye can lead to physical complications, independent of infection risk. A lens that is too tight restricts the natural flow of tears and oxygen to the cornea, causing hypoxia, or oxygen deprivation. This lack of oxygen can lead to corneal swelling or the growth of new, abnormal blood vessels into the clear corneal tissue, a condition called neovascularization.
Conversely, a lens that is too loose can move excessively on the eye, causing constant friction against the corneal surface and the conjunctiva. This rubbing can result in painful corneal abrasions, which are small scratches that break the protective epithelial layer. A corneal abrasion creates an open entryway for bacteria and other pathogens to invade the eye, increasing the risk of a corneal ulcer. The wrong fit can also cause fluctuating or blurred vision as the lens fails to remain centered.
Signs of Contact Lens Related Eye Problems
Immediate removal of the lens and prompt consultation with an eye care professional is necessary if symptoms of contact lens-related irritation or infection develop.
Common signs that indicate a problem include:
- Persistent discomfort or a feeling that something is constantly in the eye.
- A noticeable increase in tearing or discharge.
- Unusual redness or sensitivity to light (photophobia).
- Blurred or decreased vision, even after the lens is removed.
- Pain in or around the eye that worsens after lens removal, suggesting an infection like keratitis.
If any of these symptoms occur, the affected lens should be saved in its case and brought to the doctor for analysis, but it must not be worn again.