Modification & Delivery
Solutions for Rigid and Soft Lenses

SOLUTIONS FOR RIGID LENSES

Wetting Solution
Rigid contact lens materials are, for the most part, inherently hydrophobic. They therefore need to be specially treated in order to improve the wettability of the lens. Wetting solutions serve this purpose by allowing the tear to spread uniformly over the lens surface rather than break up into small drops. Since a wetting solution coats the lens, it also helps to prevent oils and debris from being transferred from the finger to the lens.

Storage or Soaking Solution
As the name suggests, the lenses are stored in a storage solution rather than being stored in a dry case. This serves to reduce the levels of pathogens contaminating the lens surface, and it will also tend to clean the lens and keep it wet. However wetting solutions are still required to render the lens more hydrophillic. Storage solutions should be changed on a daily basis.

Cleaning Solution
This solution is used to clean a lens surface which may have become smudged with dried mucus, nail polish, oil, nicotine or nonsoluble cosmetics. Cleaning solutions are routinely recommended as part of the daily lens maintenance regimen.

Combination Solution
A combination solution is an all-in-one solution with chemicals that permit cleaning, soaking, and wetting, or just soaking and wetting. The advantages of a combination solution include improved patient compliance, convenience, and to some degree, economy. While combination solutions do perform adequately, they are generally not as effective as when the individual solutions are used separately.

SOLUTIONS FOR SOFT LENSES

Soft contact lens solutions may be divided into four categories: cleaning agents; disinfection solutions both chemical and thermal; rinsing solutions; eye drops for lubricating, rewetting, and cleaning.

Cleaning Agents
Over a period of time, soft lenses can gradually become coated with debris such as protein, inorganic films, mucin, lipids, and minerals. These coatings can interfere with the clarity of vision, act as an irritant, and may cause adverse tissue responses. If these surface deposits are not regularly removed, their buildup could result in the following:

There are three types of soft lens cleaning agents. These include surface acting, oxydative, and enzyme cleaners.

Disinfection of Soft Lenses:
A distinction should be made between disinfection and sterilization. Sterilization implies the complete death of all bacteria, spores, and fungi. Disinfection, on the other hand, refers to the physical or chemical procedures that kill common pathogenic organisms, but are likely to permit other nonpathogenic organisms to survive. Disinfection is adequate for soft lens care.There are two basic methods used to disinfect soft lenses: heat or thermal disinfection, and chemical disinfection.

Thermal Disinfection: Essentially, the lenses are boiled either in a preserved or nonpreserved saline solution. The lenses are subjected to a minimum temperature of 80 degrees centigrade for 10 to 20 minutes.

There are four common systems of chemical disinfection for soft lenses:

Chlorhexidine-Thimerosol System: This was the first approved chemical disinfection system for soft lenses and was first marketed under the trade name, Flexsol. Other brand names now include Flexsol and Normol. The lens is soaked in the solution overnight and then rinsed with saline before being reinserted in the eye. A significant percentage of patients have developed allergic reactions to the thimerosol ingredient in this system.

Iodine Solutions: If a soft lens has a relatively low water content, less than 45%, the lenses may be stored in Pliacide, a solution containing 0.1% iodine, for disinfection purposes.

Quaternary Ammonium Solutions: These may be used as a combination cleaning and storage solutions. Among the companies marketing this method are Hydrocare, Allergan, and Bausch & Lomb.

Hydrogen Peroxide: This system provides excellent cleaning and disinfection for all soft lenses. However the patient must be sure to adequately neutralize the hydrogen peroxide before inserting the lens to avoid corneal damage. Brand names for this method would include Lensept, and Septicon.

The lens is first soaked in a 3% hydrogen peroxide solution for 10 minutes. It is then transferred to a second container containing normal saline solution and a catalyst where it soaks for at least 6 hours. Prior to inserting in the eye the lens is soaked in fresh saline solution for 3 minutes.

Rinsing Solutions:
Rinsing solutions may be used to rinse debris from the lens after cleaning, or to rinse the lens after chemical disinfection in order to minimize any possible adverse reactions from the chemicals.

Rinsing solutions may consist either of preserved saline, unpreserved saline, or distilled water. Unpreserved saline solution may be made from salt tablets, or from individual doses of saline such as the commercially available Unisol. If the solution is freshly prepared from salt tablets, it must be discarded after each use to avoid contamination and possible eye infection. A drawback to the use of unpreserved saline solutions is patient compliance. Instead of distilled water, some use tap water which can vary in its quality. In addition many patients do not prepare fresh saline daily.

Lubricating/Re-Wetting Solutions:
Varying degrees of ocular discomfort can occur while wearing soft contact lenses. It may be the result of certain environmental conditions such as tobacco smoke, smog, dust, or other pollution. Low humidity conditions such as those created by heaters or air conditioners in the car or work place may cause the lens to partially dehydrate causing discomfort. Inadequate tear production may also contribute toward lens dehydration. Drops, applied while the lens is on the cornea, can serve to help alleviate some of the above mentioned causes of discomfort. They include such brand names as Adapettes, Clerz, and Comfort.