Colored contact lenses are popular for changing eye color, available in both vision-correcting and non-correcting, or “plano,” varieties. These lenses are designed to alter the appearance of the iris, either subtly enhancing the natural color or completely transforming it with an opaque tint. While they offer a dramatic cosmetic effect, the fundamental question remains whether introducing a colored film over the eye interferes with normal sight. Understanding the physical mechanics of the lens and the potential health risks associated with its wear provides a clear answer.
How Colored Lenses Change Immediate Perception
Colored contact lenses are manufactured with a clear central opening designed to align over the pupil, surrounded by an opaque or translucent color layer that covers the iris. The clear pupil zone is fixed in size, typically accommodating the average pupil diameter in normal lighting conditions. This fixed design becomes problematic because the human pupil naturally changes size, dilating and constricting constantly in response to light levels.
When a person moves into a dim environment, the pupil automatically expands to maximize light intake. If the pupil dilates beyond the fixed clear opening of the colored lens, the wearer begins to look through the opaque colored pattern of the lens itself. This obstruction can result in blurred vision, a reduction in visual acuity, and the perception of glare or halos around light sources.
The colored portion of the lens can also subtly block light from entering the eye at sharp angles, potentially affecting peripheral vision. Since the lenses can shift slightly on the eye, especially when blinking, the clear zone may momentarily misalign with the center of the pupil. This movement can cause brief, intermittent visual obscuration as the colored portion passes across the line of sight.
Health Risks from Improper Use or Fit
Beyond the immediate, functional changes to perception, colored contacts pose several serious health risks if they are improperly used, fitted, or acquired without professional oversight. One danger is the risk of infection, such as microbial keratitis, which is a severe inflammation or ulceration of the cornea. Keratitis can be caused by bacteria, fungi, or parasites and is often linked to poor lens hygiene, like storing lenses in tap water or failing to use proper cleaning solutions.
Improperly fitted lenses present a mechanical risk to the eye’s surface, regardless of hygiene practices. If a lens is too tight or too loose, it can rub against the delicate corneal surface, causing painful corneal abrasions or scratches. These microscopic injuries not only cause immediate discomfort but also create entry points for infectious organisms, making the eye more vulnerable to serious complications. Purchasing lenses from non-sterile sources, like novelty shops or unverified online retailers, heightens this danger.
Another significant risk is corneal hypoxia, or oxygen deprivation, which occurs because the cornea requires a constant supply of oxygen from the air to remain healthy. Colored lenses, especially those with thicker material or denser pigment used to achieve a dramatic color change, may have lower oxygen permeability than standard clear lenses. Reduced oxygen flow can lead to corneal swelling, blurred vision, and the formation of microcysts, which may eventually cause irreversible structural damage to the eye.
Why a Professional Fitting and Prescription are Non-Negotiable
All contact lenses, including those worn purely for cosmetic purposes, are classified as Class II medical devices by the U.S. Food and Drug Administration (FDA). This classification means that even if a lens does not correct vision and is labeled “plano,” it still requires a valid prescription from an eye care professional for legal purchase and safe wear. The prescription is not just about vision correction; it is a safety measure designed to prevent serious injury.
A professional fitting ensures that the lens parameters, specifically the base curve and diameter, are measured to match the unique curvature and size of the wearer’s eye. This precise measurement is necessary to guarantee the lens sits correctly, allowing for adequate tear exchange and movement. This movement prevents the corneal damage and hypoxia associated with a poor fit. Without a professional assessment, the risks of corneal injury and subsequent vision-threatening infections are significantly increased.