Desiccation involves the loss of moisture content necessary for a contact lens to maintain its shape, flexibility, and comfort. This loss of hydration causes a structural change in the lens material, compromising its physical integrity and performance. Understanding the rate at which different lenses desiccate is important for all wearers. A dry lens can rapidly become unusable and poses a risk to eye health.
How Quickly Different Lenses Dry
The speed at which a contact lens dries depends largely on its material composition, with a significant difference between soft and Rigid Gas Permeable (RGP) types. Soft lenses, which include hydrogel and silicone hydrogel materials, are designed to hold a large percentage of water to remain pliable and comfortable on the eye. When exposed to air outside of a sterile solution, these lenses can desiccate very rapidly, often becoming noticeably dry within 15 to 30 minutes in low-humidity environments. If left out for a few hours, a soft lens will typically shrink, warp, and become extremely brittle.
Rigid Gas Permeable lenses, by contrast, are made from durable, plastic-based materials that do not rely on water content to maintain their shape. RGP lenses are designed to be firm and allow oxygen to pass through the material. While they can dry out over time, the process is far slower than with soft lenses, often taking days before the lens is fully desiccated. The primary concern for RGP lenses left exposed is the accumulation of environmental debris and residue on the lens surface, not immediate structural collapse.
Variables That Accelerate Lens Drying
Several external and material-specific factors can significantly accelerate the rate at which any contact lens loses its moisture. Environmental conditions that promote evaporation are the most common culprits, directly pulling moisture from the exposed lens surface. High ambient temperatures increase the kinetic energy of water molecules, causing them to escape the lens matrix much faster than in cooler conditions.
Air movement, such as that created by air conditioning, fans, or drafts, constantly sweeps away the thin layer of moist air immediately surrounding the lens, further speeding up evaporation. Similarly, areas with low relative humidity naturally increase the rate of desiccation by creating a steeper moisture gradient. The lens material itself also plays a role, as thinner soft lenses or those formulated with a higher water content tend to dry out more quickly because they have less material to retain the moisture.
The Physical Effects of Desiccation
Once a soft lens begins to desiccate, the polymer structure undergoes a dramatic physical transformation that renders it unusable. The lens shrinks considerably and loses its flexible, dome-like shape, resulting in severe warping or curling of the edges. As the desiccation progresses, the material hardens and becomes brittle, making it highly susceptible to micro-tears and cracks upon handling. Even if the lens is rehydrated, these microscopic imperfections in the polymer structure can persist, changing the lens’s curvature and fit.
Wearing a lens that has desiccated and been damaged introduces several significant risks to the health of the eye. A warped or brittle lens can cause mechanical trauma, such as a painful corneal abrasion (a scratch on the delicate surface of the eye). This structural damage, along with the potential for contaminants to embed themselves in the dry material, drastically increases the risk of eye irritation and serious infections like microbial keratitis. For RGP lenses, desiccation primarily leads to a buildup of tear film deposits and residue.
Safely Handling and Storing Dried Lenses
The question of whether a desiccated contact lens can be salvaged depends heavily on the lens type and the degree of damage. For a soft lens that has become hard and brittle, the consensus is to discard it immediately, as the risk of microscopic structural damage is too high to ensure safe wear. If a soft lens is only slightly tacky or stiff, it may be possible to attempt rehydration by fully submerging it in fresh, sterile contact lens solution.
This rehydration process requires patience, with the lens needing to soak undisturbed for a minimum of four hours, and often an entire 24 hours, to slowly reabsorb the solution. After soaking, the lens must be meticulously inspected for any signs of tears, warpage, or surface irregularity before considering use. Wearers must never use tap water, bottled water, or saliva for rehydration or storage. Non-sterile liquids introduce dangerous microorganisms, such as the amoeba Acanthamoeba, which can cause a severe eye infection.
Prevention strategies are the most reliable method for avoiding desiccation and maintaining lens safety:
- Always store lenses in a clean case filled with fresh, approved disinfecting solution.
- Ensure the lids are tightly sealed to prevent evaporation.
- Avoid leaving the lens case near heat sources, open windows, or in direct sunlight.
- Follow the recommended wear and replacement schedule, as an older lens can lose its ability to retain moisture effectively.