Contact lenses and their storage solutions can freeze if left inside a vehicle during cold weather. The core issue is not the lens material itself, but the aqueous solution surrounding it. When the temperature drops low enough, the solution solidifies. This freezing creates physical and chemical changes that can compromise the lens structure and the safety of the solution, posing a direct risk to eye health.
Why Contact Lens Solutions Freeze
Contact lens solutions, whether saline or multipurpose, are primarily composed of sterile water but are not pure water. These liquids contain a precise balance of salts, buffering agents, and disinfectants, known as solutes. The presence of these solutes slightly lowers the solution’s freezing point below 0°C through freezing point depression.
For most commercial solutions, the freezing point is around -1°C to -5°C. Some formulations may resist freezing down to approximately -15°C (5°F). However, a car parked overnight in winter can easily drop to temperatures far below this range, causing the solution to freeze solid. This transition introduces the risk of physical and osmotic damage to the delicate lens material.
Potential Damage to the Lens Material
When the solution freezes, the resulting ice crystals pose a mechanical threat to the soft polymer structure of the lens. These sharp formations can physically tear, scratch, or alter the surface of the lens material. Even minute abrasions on the lens can cause micro-trauma to the cornea upon insertion, increasing the potential for eye irritation and infection.
Freezing also shifts the chemical environment surrounding the lens. As pure water turns to ice, the remaining unfrozen solution becomes highly concentrated, or hypertonic, due to excluded salts and preservatives. This osmotic stress can draw water out of the lens, altering its curvature, size, and hydration level. A lens with compromised shape or water content will not fit correctly and may lead to discomfort, blurred vision, or reduced oxygen permeability.
Safe Handling of Frozen or Chilled Lenses
If your contact lenses or solution bottles have frozen, allow them to thaw slowly at room temperature. Never attempt to speed up the process using heat sources, such as a microwave or hot water. Rapid temperature changes can irreversibly warp the lens shape and degrade the solution’s chemical stability. The lenses must be left undisturbed until all traces of ice have completely disappeared.
Once fully thawed, the lenses must be removed from the frozen solution and thoroughly rinsed and disinfected using a fresh solution. Before inserting the lens, inspect it for any visible signs of damage, such as tears, cracks, or changes in shape. If the lens case or original blister pack shows cracking or leakage from ice expansion, the sterility cannot be guaranteed. The lenses should be discarded immediately to avoid the risk of serious eye infection.