Redness while wearing contact lenses results from the dilation, or widening, of the tiny blood vessels on the surface of the eye, a direct response to irritation or inflammation. The presence of a contact lens introduces a foreign body and a physical barrier to the eye’s delicate environment, making it susceptible to various forms of stress. Understanding how the lens interacts with the eye’s biology is the first step in addressing this common symptom.
How Contact Lenses Affect Eye Physiology
The cornea lacks blood vessels and must draw its oxygen directly from the air to remain transparent and healthy. A contact lens, particularly one with lower oxygen permeability, reduces the amount of oxygen reaching the corneal surface, a state known as hypoxia. In response to prolonged oxygen deprivation, the eye attempts to compensate by growing new blood vessels from the limbus, the edge of the cornea, into the clear tissue.
This abnormal growth of blood vessels, called corneal neovascularization, is a visible source of redness around the iris and can compromise vision if left unchecked. Modern silicone hydrogel lenses offer significantly higher oxygen transmissibility than older materials, but even these can cause hypoxia if worn for too long, especially overnight.
The lens rests directly upon the tear film, disrupting its natural flow and increasing the rate of evaporation, which leads to dryness. When the eye becomes dry, the mechanical friction between the lens, the eyelid, and the corneal surface increases, triggering irritation and subsequent redness. This chronic irritation can also lead to inflammation of the conjunctiva, the clear membrane covering the white of the eye.
External Triggers and Hygiene-Related Causes
Redness often arises from factors related to how the lenses are handled and maintained. The most frequent cause is poor hygiene, such as failing to wash hands before lens insertion or using tap water instead of a sterile solution for rinsing. Water can harbor microorganisms like Acanthamoeba, which can adhere to the lens surface and cause severe infections.
Over-wearing lenses past the recommended daily hours or replacement schedule allows proteins and lipids from the tear film to accumulate on the lens surface. This debris acts as a breeding ground for bacteria and creates a rough surface that irritates the cornea and conjunctiva, leading to chronic redness and discomfort. To prevent this, always discard cleaning solution from the case after each use and never “top off” old solution with new, as this dilutes the disinfectant.
Another common trigger is a sensitivity or allergic reaction to the preservatives found in some contact lens solutions or rewetting drops. This reaction causes an inflammatory response that manifests as redness and itchiness. Environmental factors also play a role, as smoke, dust, pollen, or low humidity can get trapped beneath the lens, concentrating the irritants and leading to an acute red eye reaction.
When Redness Signals a Serious Problem
While many causes of redness are temporary and resolve with lens removal, certain symptoms indicate a potentially serious eye problem that requires immediate medical attention. Redness that is accompanied by severe, sudden pain is a major warning sign, differentiating it from the mild, generalized discomfort of dryness or over-wear. Any noticeable change in vision, such as sudden blurring or haziness, also signals that the cornea itself may be compromised.
The presence of a thick, pus-like discharge or an excessive amount of tearing suggests a likely bacterial or microbial infection, such as keratitis, which is an inflammation of the cornea. Another symptom to note is photophobia, an extreme sensitivity or intolerance to light. If the redness persists for more than 24 hours after the contact lenses have been removed, or if the redness is localized to a specific spot on the eye, an urgent evaluation by an eye care professional is necessary.
Serious infections, including corneal ulcers, can progress rapidly and potentially cause permanent vision loss if not treated promptly with appropriate medication. Never attempt to “wait out” these symptoms or self-treat with over-the-counter drops, as doing so can delay the diagnosis and proper management of a sight-threatening condition. Storing the offending contact lenses in their case to show the doctor can also aid in identifying the cause of the problem.