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CONTACT LENS AND CONTACT LENS SOLUTION

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CONTACT LENS FACT

• Contact lenses were thought of as early as 1508 when Leonardo da Vinci sketched and described several forms of them.

• Contact lenses are changing area of optometry with new lenses constantly being developed.

• A contact lens, or simply contact, is a thin lens placed directly on the surface of the eye. Contact lenses are considered medical devices and can be worn to correct vision, to enhance vision or for cosmetic or therapeutic reasons

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TYPES OF CONTACT LENSES

• The three basic types of contact lenses are classified by their chemical composition and physical properties as hard, soft, and Rigid gas

permeable (RGP) contact lenses.

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HARD CONTACT LENSES

• The lenses are termed hard because they are made of a rigid plastic resin, polymethylmethacrylate (PMMA).

• The lenses are 7 to 10 mm in diameter and are designed to cover only part of the cornea.

• They float on the tear layer overlying the cornea.

• Hard lenses require an adaption period sometimes as long as a week for comfort

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• PMMA lenses are practically impermeable to oxygen and moisture (they absorb only about 0.5% water), a disadvantage to corneal epithelial respiration and to comfort.

• Care must be exercised to prevent the hard lens from resting directly on the corneal surface and causing physical damage to epithelial tissue.

• To prevent direct contact, solutions are used to wet the lens and provide a cushioning layer between the corneal epithelium and the inner surface of the lens.

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SOFT CONTACT LENSES

• Soft contact lenses are more popular than hard lenses because of their greater comfort.

• They range from about 13 to 15 mm in diameter and cover the entire cornea. Because of their size and coverage, soft lenses are less likely than hard lenses to dislodge spontaneously.

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• They also are less likely to permit irritating foreign particles (e.g., dust or pollen) to lodge beneath them. However for some patients, soft lenses do not provide the same high level of visual acuity as hard lenses.

• They are less durable than hard lenses and carry some risk of absorbing medication concomitantly applied to the eye.

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COMPOSITION OF SOFT CONTACT LENSES:

• Soft contact lenses are made of a hydrophilic transparent plastic, hydroxyethyl methacrylate, with small amounts of cross-linking agents that provide a hydrogel network. • Soft lenses contain 30% to 80% water, which

enables enhanced permeability to oxygen.

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TYPES OF SOFT CONTACT LENSES

• There are 2 types of soft contact lenses:1) Extended wear2) Daily wear contact lenses

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EXTENDED WEAR CONTACT LENSES

• Extended wear contact lenses are available for overnight or continuous wear ranging from one to six nights or up to 30 days.

• Extended wear contact lenses are usually soft contact lenses.

• They are made of flexible plastics that allow oxygen to pass through to the cornea.

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• Length of continuous wear depends on lens type and your eye care professional’s evaluation of your tolerance for overnight wear.

• It’s important for the eyes to have a rest without lenses for at least one night following each scheduled removal.

• PRECAUTION:• However, it is advisable that lenses not be left in

the eye for longer than 4 to 7 days without removal for cleaning and disinfection, else the wearer can be predisposed to an eye infection.

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DAILY WEAR CONTACT LENSES• Single use lenses (typically called 1-day or daily

disposable) are discarded after one use. Because they do not have to stand up to the wear and tear of repeated uses, single use lenses can be made thinner and lighter.

• This can improve the comfort of the lens. • Lenses replaced frequently gather fewer deposits of

allergens and germs, making these lenses preferable for patients that have ocular allergies or are prone to infection.

• Single-use lenses are also useful for people who wear contacts infrequently, or when losing a lens is likely or not easily replaced (such as when on vacation).

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RAPID GAS PERMEABLE CONTACT LENSES

• RGP contact lenses take advantage of features of both soft and hard lenses.

• They are oxygen permeable but hydro-phobic. Thus, they permit greater movement of oxygen through the lens than hard lenses while retaining the characteristic durability and ease of handling. RGP lenses are more comfortable than hard lenses.

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Specialized Uses of Contact lenses

Two types of lenses that serve a different purpose are orthokeratology lenses and decorative (plano) lenses:

Orthokeratology (Ortho-K): Orthokeratology, or Ortho-K, is a lens fitting

procedure that uses specially designed rigid gas permeable (RGP) contact lenses to change the curvature of the cornea to temporarily improve the eye’s ability to focus on objects. This procedure is primarily used for the correction of myopia (nearsightedness).

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• Overnight Ortho K Lenses:• Overnight Ortho-K lenses are the most

common type of Ortho-K. There are some Ortho-K lenses that are prescribed only for daytime wear.

• Overnight Ortho-K lenses are commonly prescribed to be worn while sleeping for at least eight hours each night.

• They are removed upon awakening and not worn during the day. Some people can go all day without their glasses or contact lenses. Others will find that their vision correction will wear off during the day.

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• The vision correction effect is temporary. If Ortho-K is discontinued, the corneas will return to their original curvature and the eye to its original amount of nearsightedness. Ortho-K lenses must continue to be worn every night or on some other prescribed maintenance schedule in order to maintain the treatment effect.

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Decorative Contact Lenses

• Decorative contact lenses are sometimes called, among other names:

• fashion contact lenses• Halloween contact lenses• color contact lenses• cosmetic contact lenses• theatre contact lenses

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• Decorative contact lenses just change the look of the eyes. They do not correct vision. They can temporarily change brown eyes to blue or make eyes look like cat eyes or vampire eyes for Halloween. The U.S. Food and Drug Administration oversees their safety and effectiveness, just like regular contact lenses.

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ADVANTAGES AND DISADVANTAGES OF VARIOUS TYPES OF LENSES

Lens Types Advantages Disadvantages

Rigid gas-permeable (RGP)Made of slightly flexible plastics that allow oxygen to pass through to the eyes.

Excellent vision... short adaptation period... comfortable to wear... correct most vision problems... easy to put on and to care for... durable with a relatively long life... available in tints (for handling purposes) and bifocals.

Require consistent wear to maintain adaptation... can slip off center of eye more easily than other types... debris can easily get under the lenses... requires office visits for follow-up care.

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Daily-wear soft lensesMade of soft, flexible plastic that allows oxygen to pass through to the eyes.

Very short adaptation period... more comfortable and more difficult to dislodge than RGP lenses... available in tints and bifocals... great for active lifestyles.

Do not correct all vision problems... vision may not be as sharp as with RGP lenses... require regular office visits for follow-up care... lenses soil easily and must be replaced.

Extended-wearAvailable for overnight wear in soft or RGP lenses.

Can usually be worn up to seven days without removal.

Do not correct all vision problems... require regular office visits for follow-up care... increases risk of complication... requires regular monitoring and professional care.

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Extended-wear disposableSoft lenses worn for an extended period of time, from one to six days and then discarded.

Require little or no cleaning... minimal risk of eye infection if wearing instructions are followed... available in tints and bifocals... spare lenses available.

Vision may not be as sharp as RGP lenses... do not correct all vision problems... handling may be more difficult.

Planned replacementSoft daily wear lenses that are replaced on a planned schedule, most often either every two weeks, monthly or quarterly.

Require simplified cleaning and disinfection... good for eye health... available in most prescriptions.

Vision may not be as sharp as RGP lenses... do not correct all vision problems... handling may be more difficult.

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CARE OF CONTACT LENSES• With the exception of disposable soft contact lenses, all soft lenses require a routine care

pro-gram that includes (a) cleaning to loosen and remove lipid and

protein deposits, (b) rinsing to remove the cleaning solution and

material loos-ened by cleaning, and(c) disinfection to kill microorganisms.

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If the lenses are not maintained at proper intervals, they are prone to deposit buildup, discoloration, and microbial contamination. The moist, porous surface of the hydrophilic lens provides an attractive medium for the growth of bacteria, fungi, and viruses. Thus, disinfection is essential to prevent eye infections and microbial damage to the lens material.

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• Hard contact lenses require a routine care program that includes (a) cleaning to remove debris and deposits from the lens, (b) soaking the lens in a storage disinfecting

solution while not in use, and (c) wetting the lenses to decrease their

hydrophobic characteristics

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• To achieve the care needs of contact lenses the following types of solutions are used:

(a) cleaning solutions, (b) soaking solutions, (c) wetting solutions, and (d) mixed-purpose solutions.

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SOLUTIONS FOR SOFT CONTACT LENSES

• Because of their porous composition, soft lenses tend to accumulate proteinaceous material that forms a film on the lens, decreasing clarity and serving as a potential medium for microbial growth. The two main categories of cleaners are surfactants, which emulsify accumulated oils, lipids, and inorganic compounds, and enzymatic cleaners, which break down and remove protein deposits.

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• Enzymatic cleaning is accomplished by soaking the lenses in a solution prepared from enzyme tablets. The enzyme tablets contain papain,

pancreatin, or subtilisin, which causes hydrolysis of protein to peptides and amino acids. Typically, these are added to saline solution, but one solution can be prepared using 3% hydrogen peroxide, which combines enzymatic cleaning with disinfection, that is, Ultrazyme Enzymatic Cleaner.

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RINSING OR STORAGE SOLUTION

• Saline solutions for soft lenses should have a neutral pH and be isotonic with human tears, that is, 0.9% sodium chloride. Besides rinsing the lenses, these solutions are used for storage, because saline maintains their curvature, diameter, and optical characteristics. The solutions also facilitate

lens hydration, preventing the lens from drying out and becoming brittle.

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• Because they are used for storage, some saline solutions contain preservatives, which while inhibiting bacterial growth can induce sensitivity reactions or eye irritation.

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DISNFECTION AND NEUTRALIZATION

• Disinfection can be accomplished by either of two methods: thermal (heat) or chemical (no heat).1) THERMAL DISINFECTION: For thermal disinfection, the lenses are placed in a specially designed heating unit with saline solution. The solution is heated sufficiently to kill microorganisms, perhaps for 10 minutes at a minimum of 80°C (176°F). It is important that after disinfection the lenses be stored in the unopened case until ready to be worn.

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CHEMICAL METHOD:

It is carried out by using hydrogen peroxide. The free radicals chemically released from the peroxide react with the cell wall of the microorganisms, and the bubbling action of the peroxide is thought to promote removal of any remaining debris on the lens.

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• To prevent eye irritation from residual peroxide after disinfection, it is necessary that the lenses be exposed to one of three types of neutralizing agents: the catalytic type (an enzyme catalase or a platinum disk), the reactive type (such as sodium pyruvate or sodium thiosulfate)

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PRODUCTS FOR HARD CONTACT LENSES:• CLEANER:• A surfactant cleaner is used by applying the

solution or gel to both surfaces of the lens.• SOAKING OR STORAGE SOLUTIONS:• Soaking solutions contain a sufficient

concentration of disinfecting agent, usually 0.01% benzalkonium chloride and

0.01% edetate sodium, to kill surface bacteria

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WETTING SOLUTION

• Typical ingredients include a viscosity-increasing agent, such as hydroxyethyl cellulose;

• a wetting agent, such as polyvinyl alcohol;• preservatives, such as benzalkonium chloride

or edetate disodium; and • buffering agents and salts to adjust the pH and

maintain tonicity