Contact Lens Care and Maintenance, Contact Lens Solution

Contact Lens Care and Maintenance

• Overview
• Contact Lens care products
• Care and maintenance of Soft contact lens and Rigid Gas Permeable (RGP) contact lens
• Contact Lens Deposits

 

Aims of Contact Lens Care and Maintenance 

• To minimize the contamination/infections
• To minimize the deposits on contact lens
• To increase the wearing compliance

Author: Rabindra Adhikary (Optometrist) Nepal

 

Daily Cleaners

Daily cleaners usually contain surfactants and are used to remove the most loosely bound foreign matter on the lens surface. Such matter includes:

• Cell debris
• Mucus
• Lipid
• Protein
• Cosmetics
• Micro-organisms

How daily contact lens cleaners work?

Surfactant molecules emulsify, dissolve and/or disperse lipid globules, debris and other lens contaminants. This is accomplished by the surfactant forming a monomolecular layer over the contaminant using the polar ends of its molecules to bind the layer to the contaminant’s surface. The ‘coated’ contaminants repel one another mutually or exhibit a lowered surface tension. Viscosity-enhancing agents such as polyvinyl alcohol or methylcellulose also facilitate cleaning.

Hypertonicity and abrasiveness are properties that have been added to enhance the efficacy of some lens cleaners. Hypertonicity results in the extraction of water from soft lenses which may help remove some soluble contaminants. Polymeric beads in some cleaners have a mildly abrasive effect on protein and other surface deposits.

The additional components in a cleaner include

• Osmolality adjusting agents,
• A buffer system to adjust the pH
• Chelating agents for removing lens contaminants and

Viscosity enhancing agents- Viscosity-enhancing agents such as polyvinyl alcohol or methylcellulose also facilitate cleaning.

 

How to clean contact lenses with Daily Cleaners?

Here are some steps for cleaning contact lenses.

• Wash hands thoroughly, soap or oil without fragrance
• Put the lens in the palm
• 2-3 drops of daily cleaners
• Press with to and fro motion 15 sec

It is important to understand that performing the cleaning is more important than the brand or type of cleaner used Cleaning should be done with:

• All lens types including disposables.
• All care systems, especially multipurpose solution-based care.
• The mechanical action of rubbing and rinsing reduces significantly the amount of loose debris and the number of microorganisms on a lens.
• Rubbing also enhances the efficacy of the cleaning solution’s surfactant properties

Rinsing Solution (Rinsing solution for contact lenses)

After cleaning, lenses should be rinsed. Rinsing performs a variety of functions. Buffering agents are included in rinsing solution formulations so that their pHs approximate that of tears. The pH of normal tears is, on average 7.2, but is subject to individual variation. To enhance the compatibility of the solution and tear pHs at lens insertion, the solution is normally buffered lightly.

Saline

• Once-common form of rinsing solution.
• Risk of contamination so discards in 2 weeks.

Homemade saline has no role in contact lens care. In the Donzis et al. (1987) study, homemade saline was contaminated with bacteria and some preparations were contaminated with Acanthamoeba sp. Meanwhile, the preserved saline solution remained uncontaminated for a period of up to 21 days after opening.

 

Disinfecting Agents

Purpose of Disinfection.

Contact lenses may compromise the eye’s natural defence by the followings:

• Inhibiting tear film washing action
• Introducing more microorganisms
• Compromising epithelial barrier functions

Functions of Disinfecting solutions

They kill or deactivate potentially bacteria, fungi, virus, amoebas. It maintains the contact lens hydration

Terminologies used in Disinfection

• Sterilization is the killing of all microbial life forms, a situation impossible to achieve with normal lens care products and procedures.
• Disinfection is a dynamic process, usually preceded by a cleaning and rinsing step, intended to kill and/or remove microbial and viral contaminants from contact lenses.
• Preservation is the killing or inhibition of the growth of a select range of microorganisms to prevent product spoilage during consumer use.
• The choice of preservative is governed to a large extent by the resistance of the microbial targets and the sensitivities of the eye exposed to the preservative via contact lenses or eye drops.

 

Disinfection Mode of action

• Cell membrane disruption
• Enzyme inhibition
• Protein coagulation/ complex formation

 

Disinfection System

• Thermal: Heat-based disinfection systems use heat in the range from 70°C to 125°C to kill or deactivate living lens contaminants. Heat disinfection systems generally decrease lens life span and eventually cause lens discolouration.
• SOFT MATE – Barnes Hind

Bausch & Lomb Thermal Disinfecting System

Soft contact lenses are placed in the lens case with saline solution and heated to 70 – 80°C for 10 – 20 minutes.
The controlled heating and automatic shut-off prevent overheating and possible shortening of lens life.

Chemical Disinfection

A wide variety of types exist on chemical disinfection of contact lenses. Two types discussed here

1. Disinfectant-based solutions (Cold chemical) include Thimerosal, chlorhexidine Gluconate, BAK, Sorbic acid.
2. Hydrogen peroxide-based solutions (Oxidative)

 

Thimerosal

It is a mercurial antibacterial also effective as an antifungal. Thimerosal has Many Drawbacks such as

1. Cytotoxic activity to the corneal epithelium
2. Cessation of mitosis cell division
3. Delayed hypersensitivity reactions showing subepithelial opacities.

 

Chlorhexidine Gluconate

• A biguanide antimicrobial) uptake and release has also been studied because of its historic use by manufacturers in combination with thimerosal or other agents to enhance its effectiveness
• CHG is adsorbed onto RGP lenses (siloxane acrylates) as a monolayer until they become saturated and no further uptake occurs
• Concentrations: 0.0025-0.006%
• Hypersensitivity reactions may occur

Benzalkonium Chloride (BAK)

Benzalkonium Chloride creates cytotoxic reactions in the corneal epithelium in a shorter period of time than thimerosal or chlorhexidine. BAK’s uptake by rigid gas permeable (silicone acrylate) lenses has been shown to be one of self-aggregation whereby the positively charged molecules continue to bind to the negatively charged surface of the lens until they reach toxic concentrations. BAK release onto the cornea from soft and rigid contact lenses have been shown to be beyond the critical limits of safety

 

Sorbic acid

Sorbic acid has antibacterial and limited antifungal activity. Its concentration in SCLs has not been shown to cause the death of the corneal epithelial cells. Sorbic Acid causes yellow or brown discolouration of the contact lens due to its interaction with Amino Acid (lysine) and tear protein.

 

Benzyl Alcohol

It is a disinfectant and preservative for RGP and PMMA lens.

• It is unsuitable for use with soft contact lenses
• Benzyl Alcohol is non-cytogenic and relatively non-sensitizing
• It is bactericidal and viricidal but ineffective against Pseudomonas aeruginosa in low concentrations like other alcohols (isopropyl alcohol, isopropanol, ethanol), it behaves like a lipid solvent

 

Chlorbutanol 0.5%

• It is a chlorinated alcohol preservative with a broad spectrum of action.
• It is, however, slow-acting against and bacteria and has a distinctive odour.
• Chlorbutanol  is effective in acidic pH and used along with other preservatives

 

EDTA

EDTA is not strictly preservatives. They are variously described as preservative enhancers, preservative potentiators and chelating agents, EDTA’s action removes, by chelation, divalent cations such as calcium and magnesium ions from solutions and/or cell walls of gram-negative organisms. ETDA does not bind to lens materials significantly and is normally used in combination with other preservatives. ETDA has a synergistic action with BAK, which enhances the effectiveness of the blended solution

 

Biguanide

The first biguanide used as chlorhexidine (CHX). Polymeric biguanides include – PHMB, PAPB. Polyhexanid

Polyhexanide (PHX) properties include:

• Polyhexanide =  polyhexamethylene biguanide, PHMB Fast-acting, broad-spectrum antimicrobial.
• Good fungicide.
• Variable virucide.
• Good Gram-negative (e.g . Pseudomonas spp.) biocide.
• Broad range of pHs (4-IO).
• Stable (>2 years).
• Heat stable to > 140°C (autoclavable).
• Odourless, clear, colourless, non-foaming.
• Miscible with water in all proportions.
• Incompatible with chloride, calcium and magnesium ions

 

Polyquad

Polyquad is the marketing name for a high molecular weight (polymeric) quaternary ammonium compound: Poly(quaternium), polidromium chloride, onamer M. This type of preservative is used in both rigid and soft lenses in concentrations of 0.001 – 0.005 %. Its high molecular weight of 5000 restricts its entry into lens materials thus minimizing ocular reactions

 

Disinfectant/Preservative Sensitivity

The most common observable sign of this condition is mild conjunctival redness in both eyes which affects the exposed nasal and temporal quadrants as well as the upper and lower bulbar conjunctiva.

 

Tablet-based Disinfecting system

• Chlorine tablet system
• Halane(sodium dichloro isocyanurate)
• Halazone(poly dichloro sulphanoyl benzoic acid)

E.g Alcon Softab, Sauflon Aerotab

• Chlorhexidine  E.g Optim eyes

 

Hydrogen Peroxide based solution

PH 3-4; suitable for all lens type. Hydrogen peroxide-based disinfection systems may be either preservative-free or preserved and can be divided into two main types:

1. One-step systems
2. Two-step systems

Hydrogen peroxide disinfection systems are normally formulated with a 3% peroxide concentration For a lens to be wearable following disinfection, neutralization is required. Various neutralization techniques have been designed by manufacturers to simplify the disinfection and neutralization steps and thereby lessen the likelihood of non-compliance or discomfort on insertion. Most systems catalytically decompose hydrogen peroxide into saline and oxygen. Disinfection in hydrogen peroxide is reasonably effective in 10 – 15 minutes for bacteria, 1 hour for fungi and 3-6 hours for acanthamoeba

Advantage of hydrogen peroxide

• Very effective

 

Disadvantages

• If stored for a longer period of time or exposed, the solution may have already gone oxidation.
• In this case, the desired effect is not obtained. And there is no proper way we can monitor how much percentage of hydrogen peroxide has undergone oxidation.
• It is not perfectly compatible especially with high water content, ionic contact lenses in that it can reversibly alter lens parameters and water content
• Once it is neutralized, a peroxide system has no antimicrobial power and can sometimes cause irritation in the eye if not neutralized properly

 

One-step procedure

One step procedure is formulated so that the peroxide disinfection and neutralization are performed during the recommended time. With tablet-using systems, a delay is applied to the neutralization phase. With disc-based systems, no delay is applied to the neutralization phase. Regardless of which of these systems is used special vented lens cases are required to allow the oxygen generated to escape.  One step systems use either a catalytic (platinum) disc or a time-delayed catalase tablet.

 

Two-step procedure

When neutralization is performed as a separate step, the system is called a two-step system.
Step 1: Disinfection
Step 2: Neutralization

Very early systems ‘neutralized’ peroxide using premeasured quantities of sodium bicarbonate for a minimum of 10 minutes.

In fact, the process was not true neutralization and usually took longer than 10 minutes. Rather, the bicarbonate altered the solution pH (upwards) to levels at which peroxide was inherently less stable. The peroxide solution then began to decompose slowly into water and oxygen.  With two-step systems, it is recommended that lenses are stored overnight in the peroxide and neutralized immediately before lens usage.

 

How to use hydrogen peroxide contact lens solution?

• Be sure to use the special contact lens case that comes with your hydrogen peroxide contact lens solution.
• Be sure to leave your contacts in the solution for at least 6 hours to allow the neutralizing process to finish.
• For the purpose of neutralization substances like sodium pyruvate, sodium thiosulphate, sodium sulphite, catalase and sodium bicarbonate have been used

 

Protein Remover for Contact Lenses

• Protein removers, also known erroneously as enzymatic cleaners, are included in the care systems for soft contact lenses, and some RGP lenses, that are not replaced regularly (>1month).
• Not all protein removers are enzyme-based. Those that are, are usually supplied in tablet form.
• Chemical-based systems are usually supplied as ready-to-use liquids. These cleaners are effective in loosening tightly bound protein deposits. However, they cannot be expected to remove all proteins.
• Also marketed in the name of intensive cleaners
• Protein treatment is usually done weekly or at a frequency dependent on the rate of patient protein deposition.
• Heavy protein depositors, especially ionic high water material lens wearers, may require an increased frequency.
• Lenses should be soaked in the remover for 15 minutes to two hours, depending on the type of protein remover used and rate of protein build-up.
• Enzymes used include papain, subtilisin, pronase and pancreatin.

 

Papain

• Derived from papaya plant
• Bind to CL materials and can cause sensitivity rxn
• Short soaking time: 15 min

 

Pancreatin

• Pig panreas derivative
• Cleaning efficacy similar to papain.

 

Subtilisin

• Derived from bacillus bacteria
• Low toxicity: used in food products
• Less specific binding characteristics
• More effective than papain & pancreatin
• Enzyme tablets act as protein removers by cleaving the peptide bonds in tear proteins deposited on contact lens surfaces

 

 

Rewetting Eye Drops and Lubricants

Tear fluid supplements are often used by contact lens wearers to:

• Promote comfort.
• Overcome the sensation of dryness that can occur with soft lenses due to insufficient lubrication by the tear film.
• Rehydrate the lens and flush debris from the surface of the eye and lens.
• Reduce the deposit-induced friction between the eyelids and the corneal surface.
• Cushion the lens on the eye.

 

Lens Storage and Cases

• To avoid contamination, the lens case should be rinsed after every use and the lenses stored in a fresh solution.
• A soiled lens case can be the cause of ocular irritation when contaminants are transferred to a contact lens and from the lens into the eye. It can also be the cause of lens discolouration.
• If a case is heavily contaminated with microorganisms, it may reduce the efficacy of the disinfection system by exceeding the disinfectants capacity to kill the target micro-organisms.
• Bacterial contamination of storage cases for both soft and rigid contact lenses has been reported by a number of investigators
• Biofilm or glycocalyx formation on the surface of contact lens storage cases can harbour Pseudomonas aeruginosa and Serratia marcesens.
• The biofilm is produced by the bacteria themselves. It protects the host bacterial cells from chemical or preservative attack and traps nutrient particles and organisms. Human biofilm formed around CL is beneficial for CL adaptation because it makes surface biocompatible Bacterial biofilm is, on the other hand, is hazardous
• Pseudomonas aeruginosa and Serratia marcesens are also able to produce their own biofilm in storage cases.

How to clean the contact lens case

Here are some steps about how to clean a contact lens case.

• Scrub with a toothbrush and detergent weekly. Oil-free soaps or detergents are recommended for this step.
  Rinse with hot water and rub thoroughly with a clean, dry tissue. Acanthamoeba can be killed at temperatures of ≥70°C. Rubbing will help disrupt the biofilm that may be forming on the case surfaces.
• Air dry. Keeping the lens case dry will prevent colonization by micro-organisms such as protozoa that thrive in moist or wet environments.
• Frequent Replacement of case

 

Disclaimers: This post is for educational purpose only, Author and Eye Health Nepal both have no financial interest in the above products.