We still see allergies to the preservatives in contact lens solutions in our Fort Collins Contact Lens Clinic but at a much lower frequency than in the past.
Thimerosal, (sodium ethylmercurithiosalicylate) is an older contact lens solution preservative whose composition is about half mercury. It as commonly used in very low doses in contact lens disinfecting solutions is an excellent preservative but causes a reasonably high number of allergic reactions. It has been used in childhood vaccines and a subject of controversy over the years as a possible cause of autism. There are no significant studies to confirm a relationship, but similar to contact lens solutions, it is being phased out. You will often see vaccines that are touted as mercury free.
Chlorhexidine is a chemical antiseptic that is very effective at killing bacteria. It was also widely used in the past in contact lens solutions prescribed by eye doctors but frequently caused red eyes, vague forms of eye irritation, and sometimes significant conjunctivitis and discomfort. Like Thimerosal, it has largely been phased out of contact lens care and we never reccomend it in our Ft Collins Eye Practice. It is still widely used in the dental field to treat gum disease and as a disinfectant.
Benzalkonium chloride was used in the past and is still used today is some nasal sprays, cleaning solutions, and various other hygienic products. It is a good disinfectant but at high enough levels may not only serve as an allergen but cause serious damage to the corneal tissue the contact lens rests on.
The next generation of sensitive eyes contact lens solutions proved to have about the same rate of allergic reactions, just for different people. Switching often cured the problem for those allergic to former solutions but created problems for new users.
Many generations of solutions have since come to pass. Today the large molecule preservatives are favored by optometrists since they fail to build up in the contact lens matrix, exceeding the pore size of the lenses.
The problem today rests in generic contact lens solutions, often colored and labeled to look like the brand solutions. Sometimes they are OK, at other times they are using these older toxic preservatives that should have been off the market a long time ago. To compound the confusion, the formulations may change in the middle of the shelf for the same generic brand, even though the box appears identical.
The best bet today is to stick with a brand name solution your eye doctor reccomends or use one of the hydrogen peroxide based systems. The drawback to hydrogen peroxide has always been it is too easy to make a mistake, and hydrogen peroxide is very uncomfortable when placed in your eye without neutralization!
Spend a few extra minutes during your next visit to the optometrist and ask their advice on what is the best contact lens care regimin avaialbe to keep your eyes healthy and seeing well.