Monthly contact lenses are medical devices approved for extended use, typically 30 days, before replacement. Their convenience reduces the frequency of replacement and the daily routine of cleaning and storage. These lenses are engineered for durability, allowing for a much longer wearing cycle than daily or bi-weekly options.
The Science Behind Extended Wear Materials
The ability to wear a contact lens for up to a month results from advancements in polymer chemistry, specifically Silicone Hydrogel (SiHy) materials. The cornea requires a continuous supply of oxygen from the air to remain healthy; sleeping with a lens restricts this flow. Older soft lenses (hydrogels) relied on water content to transport oxygen, often causing hypoxia when worn too long.
Modern SiHy lenses incorporate silicone, which is highly permeable to oxygen, allowing significantly more gas to pass to the cornea. Oxygen transmissibility is measured by the Dk/t value (‘Dk’ is permeability, ‘t’ is thickness). High Dk/t lenses minimize the risk of hypoxia-related complications, such as corneal swelling and redness, even during overnight wear.
Understanding Different Monthly Wear Schedules
Monthly contact lenses follow two distinct wearing schedules.
The first is “Extended Wear,” where the user wears the lenses during waking hours for up to 30 days but removes, cleans, and stores them nightly. This schedule uses a longer replacement cycle than conventional lenses.
The second is “Continuous Wear,” where lenses are worn day and night, including while sleeping, for up to 30 consecutive days. Not all monthly lenses are approved for continuous wear, and sleeping in lenses must be recommended by an eye care professional. Even with high oxygen flow, sleeping in any contact lens increases the risk of complications, making this schedule suitable only for certain individuals.
Essential Hygiene and Safety Protocols
A strict hygiene protocol is necessary to maintain eye health, even for lenses approved for continuous wear. If a lens is removed nightly, it must be cleaned using a “rub and rinse” method with the recommended solution to physically remove deposits and debris. The lens must then be submerged in fresh solution for the manufacturer’s specified disinfection time, often at least six hours.
Never use tap water, saliva, or expired solution for cleaning or rinsing, as these introduce harmful microorganisms. The lens case is a potential source of contamination and should be rinsed with fresh solution, allowed to air dry upside down, and replaced every two to three months. Lenses must be discarded precisely at the end of the 30-day period, as the material degrades and accumulates deposits over time.
Identifying Potential Complications
Extended wear requires awareness of potential risks. The primary concern is Microbial Keratitis, a severe eye infection that can lead to permanent vision loss if not treated promptly. The risk of this infection is significantly higher when lenses are worn while sleeping.
Other potential issues include Corneal Ulcers (open sores on the eye’s surface) and Giant Papillary Conjunctivitis (GPC), an allergic reaction to deposits on the lens. Warning signs that require immediate lens removal and professional consultation include:
- Persistent eye redness.
- Sudden or worsening pain.
- Excessive light sensitivity.
- Any abrupt change in vision.