Contact Lens Solutions | November 17, 2008 Issue - Vol. 86 Issue 46 | Chemical & Engineering News
Volume 86 Issue 46 | p. 71 | What's That Stuff?
Issue Date: November 17, 2008

Contact Lens Solutions

Companies strive to balance ingredients in one-step,user-friendly solutions
Department: Science & Technology
Credit: Dreamstime
Credit: Dreamstime

SLIPPING CLEANING FLUID into one's eye is not likely to be high on anyone's list of hobbies, but contact lens wearers do it daily. After spending the night in cleaning solution, a dripping contact lens is inserted into the eye—ideally, without causing any discomfort.

Historically, putting lens cleaning solution in the eye wasn't an option. Twenty years ago, cleaning contact lenses was generally a multistep process requiring a cleaner, a disinfecting agent, saline for rinsing off the cleaner or disinfecting agent, and an occasional enzyme tablet to remove protein buildup from tear fluid.

But the more steps there are, the more likely wearers won't follow them correctly, or at all—increasing the likelihood of sight-threatening infections. Teenagers just starting to use contact lenses are particularly likely not to comply with complicated systems, says Srini Venkatesh, senior director for lens care product development at Bausch & Lomb.

In response, manufacturers developed one-step systems for the soft lenses that dominate the market today. These systems come in two types, peroxide and multipurpose solutions. Both contain cleaners, such as bisphosphonate compounds, to break down proteins adhering to lenses or surfactants, such as block copolymers, to interfere with the protein-lens interactions. The solutions also typically contain moisturizing or conditioning agents such as cellulose, propylene glycol, or polyvinyl pyrrolidone, ingredients that Ciba Vision's global head of research, Lynn Winterton, hopes will make users say, "Wow, this feels great!" There are also buffers to maintain an eye-friendly pH and preservatives to maintain shelf life.

The difference between the peroxide and multipurpose solutions lies in how they disinfect. Peroxide systems, as their name would indicate, use peroxide as the disinfection agent. They typically involve two components: a 3% peroxide solution and a neutralization catalyst. While the peroxide does a fine job of killing whatever microbes might have latched onto lenses, it's not very eye-friendly, so a platinum, palladium, or silver catalyst is used in the contact lens case to completely neutralize the solution by reducing the peroxide to form oxygen and water.

The peroxide neutralization reaction itself, as well as the O2 product bubbling through the solution, may further help to kill microbes, Venkatesh says. Typically, a lens wearer puts their lenses in the case with the peroxide solution and catalyst, and returns four to six hours later to find their lenses ready to wear.

Using polymers instead of monomers provides effective antimicrobial activity while still being gentle to the eye.

Peroxide, of course, will oxidize many things other than microbes, so one tricky aspect to solution formulation is to find cleaners or conditioning agents that can survive storage in a peroxide solution without degradation.

In contrast to peroxide solutions, multipurpose solutions typically use a polymeric disinfection agent such as polyhexamethylene biguanide or polyquaternium, which incorporates quaternary ammonium centers. As with peroxide solutions, the disinfectant presents the biggest challenge to solution developers, although for a different reason: The solution, including the disinfectant, must be gentle enough that lens wearers can put their lenses directly into their eyes without rinsing.

The polymers, therefore, are a compromise. They're made from monomeric building blocks that are effective at killing microbes but are too harsh to go in the eye in that form. Using polymers instead of monomers provides effective antimicrobial activity while still being gentle to the eye.

One active area of contact lens solution research, Winterton says, involves finding ways to eliminate preservatives from solutions so there's one less thing going into the eye. Another is to develop dual-purpose conditioning agents that not only will keep lenses comfortable but will also repel microbes.

Venkatesh notes that contact lens solutions offer chemists unique challenges. The solutions have six or seven ingredients whose compatibilities must be balanced, but overall more than 95% of the content is water. In addition to being mindful of chemical interactions, solution chemists must also be cognizant of ingredients adsorbing to bottles and pipes. "When you start at a really low concentration, if it drops even by 10% you can have huge differences in performance," Venkatesh says. "There's an art to developing solutions and a lot of skill."

Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
G bayne  (February 18, 2013 11:16 AM)
question...just read that a man in the Australian outback survived for 3 days by drinking contact solution. Is there anything in there that would make you ill or kill you in an emergency. Sounds like something that I might want to keep on hand in my back pack.
Adrian Stovell  (May 4, 2015 2:18 PM)
I saw that on a Bear Grylls episode.. I don't suggest you keep contact solution in your backpack just in case of an emergency to drink it. Rather stick to good old water.. In the episode it was said that they oak went on a short walk which turned into a long one and he ended up getting lost for days without any water. The only liquids that he had available was the bit left in his disposable contact lens sachets.. He took a chance but it apparently saved his life .. But in my opinion, never go into nature with out some water and a pack of salty cracks;) ...
Jyllian  (May 12, 2015 5:22 PM)
I agree with Adrian. In an emergency, if all you have is contact lens solution, it's probably fine to drink the non-peroxide variety. But I wouldn't pack contact lens solution *instead* of water.
Leave A Comment