Why should you never top off old solution in a lens case?

Topping off dilutes the disinfectant concentration, reducing its ability to kill microorganisms. Organisms that survived in the old solution continue to multiply in the weakened fresh-plus-old mixture. This significantly increases the risk of contact lens-related infections, including serious ones like Acanthamoeba keratitis. Always discard all old solution and refill with completely fresh solution.

What is solution-induced corneal staining (SICS)?

SICS is diffuse punctate corneal staining that occurs when certain multipurpose solution formulations interact with specific contact lens materials, particularly some silicone hydrogels. It typically appears at the 2-hour point after lens insertion and is caused by the solution preservative interacting with the lens surface chemistry. Switching to a different MPS brand or hydrogen peroxide care usually resolves the issue.

Multipurpose Solutions: Cleaning, Disinfection, and Proper Use

Q: Why is the rub-and-rinse step important even for 'no-rub' solutions?

The mechanical rubbing action physically disrupts biofilms, which are organized colonies of microorganisms that resist chemical disinfection alone. Studies consistently show that rub-and-rinse removes significantly more microorganisms than soaking alone. The rubbing also physically removes protein and lipid deposits that chemical cleaning alone may not fully address.

The All-in-One Solution

Multipurpose solutions (MPS) are the most commonly used contact lens care products. They perform multiple functions with a single solution, simplifying the daily care routine for soft contact lens wearers. Understanding how they work and how to instruct patients on proper use is essential for preventing contact lens-related complications.

Functions of MPS

A single multipurpose solution performs four essential care functions:

Cleaning: Surfactant agents in the solution loosen and remove deposits, debris, and microorganisms from the lens surface
Rinsing: The solution washes away loosened material after cleaning
Disinfecting: Antimicrobial agents kill bacteria, fungi, and other pathogens that could cause eye infections
Storing: The lens soaks in the solution overnight, maintaining hydration and continuing disinfection

The Rub-and-Rinse Technique

The rub-and-rinse method is the recommended technique for using MPS, even for solutions labeled "no-rub":

Wash and dry hands thoroughly
Place the lens in the palm of one hand
Apply several drops of MPS to the lens surface
Gently rub the lens with a fingertip in a back-and-forth (not circular) motion for 20 seconds
Rinse the lens thoroughly with additional MPS
Place the lens in a clean case filled with fresh MPS
Repeat for the second lens
Soak for the minimum recommended time (usually 4-6 hours)

The mechanical rubbing step is arguably more important than the chemical disinfection. Rubbing physically disrupts biofilms (organized colonies of microorganisms that are resistant to chemical disinfection alone). Studies consistently show that rub-and-rinse removes significantly more organisms than soaking alone, even with solutions labeled "no-rub."

Disinfecting Agents in MPS

Common antimicrobial agents used in multipurpose solutions:

PHMB (polyhexamethylene biguanide): Also called polyhexanide. A widely used disinfectant effective against bacteria and fungi. Used at very low concentrations (0.0001%) to minimize toxicity
Polyquad (polyquaternium-1): A quaternary ammonium compound that binds to and disrupts microbial cell membranes. Generally well-tolerated due to its large molecular size, which limits corneal penetration
Alexidine: A biguanide similar to PHMB, used in some newer formulations

These agents must balance antimicrobial effectiveness with biocompatibility. Too concentrated, and they cause corneal toxicity. Too dilute, and they fail to adequately disinfect.

Contact Lens Case Care

The contact lens case is a frequently overlooked source of contamination. Proper case care is as important as proper solution use:

Empty and rinse the case with fresh MPS after each use (never use water)
Air dry the case upside down on a clean tissue between uses
Never top off: Always discard old solution and refill with fresh solution. Topping off dilutes the disinfectant and allows organisms to survive
Replace the case every 3 months at minimum (many solution bottles include a new case)

Case contamination is one of the leading causes of contact lens-related infections, including Acanthamoeba keratitis. During follow-up visits, ask patients to bring their lens case for inspection. Check for visible biofilm (a slimy coating on the case interior), discoloration, or damage. A contaminated case should be replaced immediately.

Solution Compatibility

Not all MPS formulations are compatible with all contact lens materials:

Some MPS cause solution-induced corneal staining (SICS) when used with certain silicone hydrogel materials. This appears as diffuse punctate staining at the 2-hour follow-up visit
Always verify that the MPS is approved for use with the patient's specific lens material
If a patient develops corneal staining with their current solution, switching to a different MPS brand or to hydrogen peroxide care often resolves the issue

What Not to Do

Never use tap water: Water can contain Acanthamoeba and other organisms. Water should never contact lenses or lens cases
Never use saliva: The mouth contains numerous bacteria that can cause serious eye infections
Never mix solutions: Different brands should not be used interchangeably in the same care step
Never reuse solution: Solution used for storage must be discarded after each use
Never sleep in daily wear lenses after MPS storage: MPS is designed for daily wear schedules unless the lens is specifically approved for extended wear

Topping off old solution in the lens case instead of using fresh solution. Topping off is one of the most common and dangerous compliance errors. It dilutes the disinfectant, reduces antimicrobial effectiveness, and allows surviving organisms to multiply. Always emphasize complete case emptying and fresh solution with every use.

Key Takeaways

MPS cleans, rinses, disinfects, and stores in one solution
The rub-and-rinse technique is essential for disrupting biofilms and removing deposits
Common disinfectants include PHMB, Polyquad, and alexidine
Never top off old solution; always use fresh solution for each storage cycle
Replace the lens case every 3 months minimum
Never use tap water, saliva, or mixed solutions with contact lenses