In this month’s OA Corner, we ask: why are there so many different ingredients in contact lens solutions?
You may have looked at the list of ingredients on contact lens solution bottles and wondered about the purpose of these ingredients. So let’s look at the more common ingredients, and why they are added to the solutions.
To begin with, it is useful to consider the purpose of a contact lens solution. The solution should be able to effectively clean the lens and remove any deposits, and ensure that when the lens is inserted into the eye it is comfortable and does not sting.
The solution should also disinfect the lens, as this is important to prevent any infection. Protein, lipids and calcium can adhere to the lens during wear and if these deposits are not removed, the cleaning and disinfection of the lenses will be compromised. This means that lenses need to be cleaned by rubbing and rinsing with a cleaning solution prior to overnight soaking.
The rub and rinse solution needs to remove protozoa and viruses, and the soaking solution should combat bacteria and fungi. With this in mind, we will consider the different ingredients that are added to contact lens solutions in order to achieve these requirements.
Preservatives
Preservatives are added to a solution to prevent microbial growth and to keep the solution sterile once the bottle has been opened. Some patients can develop an allergic reaction to preservatives, and preservative-free solutions are available. Chlorhexadine and polyhexanide are two examples of preservatives.
Chelating agents
Chelating agents are added to increase the effectiveness of the added preservative. This means less preservative can be added for the same effect, which makes an allergic reaction less likely. An example of a chelating agent is EDTA (ethylene diamine tetracetic acid).
Surfactants
Surfactants are added to a solution to clean the lens by removing surface deposits. Poloxamine and miranol are examples of surfactants.
Wetting agents
Wetting agents are added to help the solution spread over the lens surface. They also increase the wettability of the lens material itself. An example of a wetting agent is polyvinal alcohol.
Viscosity agents
Viscosity agents are added to rigid gas permeable lens solutions to thicken the solution. This provides a cushion between the eye and the lens, which makes lens insertion more comfortable. An example of a viscosity agent is methylcellulose.
Buffers
Buffers are added to maintain the PH of the solution within a similar range to the pH of the tears, which prevents stinging. An example of a buffer is sodium phosphate.
Tonicity agents
Tonicity agents are added so the salt concentration of the solution is similar to the salt concentration of the tears, which ensures the osmotic pressure is the same as the tear film. This ensures an equilibrium is maintained between the water in the lens and the ocular tissues.
There are many different contact lens solutions available; some contain preservatives and some are preservative free. The different ingredients mean that it is not advisable for patients to switch between different solutions without checking with the prescriber first, and advice should always be sought.
Next time you pick up a bottle of contact lens solution, have a look at the list of ingredients and see how many you can identify.
Sue Deal FBDO R is a practising dispensing optician, ABDO College examiner, senior tutor and supervisor for dispensing opticians. She is also a practice visitor and external moderator for ABDO. She was recently awarded the ABDO Medal of Excellence for her outstanding services to the profession.
OA Corner Part 17: Patient complaints Part 2
OA Corner Part 16: Patient complaints Part 1
OA Corner Part 15: Dry eye disease
OA Corner Part 14: Occupational dispensing
OA Corner Part 13: PPLs demystified
Links to Parts 1-12 can be found here.