Ординатура / Офтальмология / Английские материалы / Medical Contact Lens Practice_Millis_2005

gentle rubbing with a contact lens disinfectant solution. Patients may complain of a bad taste or even nausea.

Ciprofloxacin has been used experimentally in soft contact lenses to achieve a greater concentration than was possible with frequent topical drops,6 but the effect diminished after 3 hours.

Ofloxacin

Ofloxacin is similar to ciprofloxacin, but is more water soluble. It can rarely cause local irritation, photophobia, dizziness and numbness, as well as headache and nausea. It has been shown to be as effective when applied twice a day as if given four times a day.7

Tetracyclines

The tetracycline drugs include oxytetracycline, chlortetracycline, tetracycline, doxycycline and minocycline. They are bacteriostatic, inhibiting protein synthesis. They are effective against a wide range of Gram-positive and -negative bacteria and chlamydia.

Oral tetracyclines, which are used for a number of ocular conditions, are absorbed via the gastrointestinal tract and should be given between meals, with an empty stomach because substances such as aluminium hydroxide, calcium and magnesium salts, and iron preparations bind to the drug and reduce absoption. Doxycycline and minocycline are well absorbed and can be taken with meals. Systemic tetracyclines may cause diarrhea, nausea and vomiting.

Tetracyclines become absorbed in bone. This causes a yellow discoloration in the adult, but does not appear to have any other adverse effect, but bone growth is retarded in children and teeth are discolored and the tooth enamel is affected. These drugs should therefore be avoided in children under twelve years of age. There are no reports of discoloration of teeth from topical tetracycline.

Phlyctenulosis mainly affects children and is believed to be due to a delayed hypersensitivity to staphylococci that responds to topical tetracycline.

Patients with ocular rosacea commonly suffer from chronic blepharoconjunctivitis and meibomitis.

Systemic tetracycline given as 250 mg four times a day for 4–6 weeks gradually reducing to 250 mg daily for six months is an effective treatment that controls, but does not cure the condition, although the effects of treatment may last for several months after it stops.

Tetracycline acts by inhibiting the production of bacterial lipase by the ocular flora, which results in a reduction in fatty acid production, or by the inhibition of the synthesis of lipids by the glands.8 It is now more usual to prescribe a longer acting preparation such as doxycycline once a day. It does not need to be used as frequently.

Tetracyclines do not have a part to play in the treatment of microbial keratitis because Pseudomonas aeruginosa is resistant to this group of drugs.

Chlamydial disease is seen as a chronic follicular conjunctivitis and keratitis acquired from the genital tract. It occurs most often in young adults. Treatment is with oral tetracycline 250 mg four times a day for 6 weeks, or doxycycline 300 mg weekly for 3 weeks, or 100 mg daily for twelve weeks. For those in whom tetracycline is contraindicated erythromycin 250 mg four times a day for 6 weeks is a satisfactory alternative.

Tetracyclines have a weak anticollagenolytic action and systemic use aids healing in persistent epithelial defects. Tetracyclines have also proved useful in the treatment of recurrent corneal erosions.8

Fusidic acid

Fusidic acid (Oc. Fucithalmic®) is an ointment that inhibits bacterial protein synthesis and is used mainly for Gram-positive infections, particularly staphylococci, but there is a high rate of resistance. In cases of conjunctivitis it is used twice daily, which enhances compliance, but it cannot be used in conjunction with contact lenses.

Anti-acanthamoebic drugs

Acanthamoeba infection is characterized by pain that is out of proportion to the findings. It causes keratitis, neurokeratitis and a ring infiltrate late in the disease. It can result in a serious loss of vision.

Treatment is with propamidine isethionate and polyhexamethylene biguanide.

Propamidine isethionate

Propamidine isethionate is an aromatic diamidine, which is not useful in bacterial infections, but does act against both cysts and trophozoites. It acts by inhibiting DNA synthesis. Propamidine isethionate may be toxic in long-term use and can cause linear intraepithelial cysts. It is available in the UK, without prescription, as Brolene® drops, and dibromopropamidine isethionate, which is marketed as an ointment. These are not available in the USA.

Polyhexamethylene biguanide

Polyhexamethylene biguanide (PHMB, polyhexanide)9 and chlorhexidine, to which it is related, are cationic antiseptics. PHMB is cysticidal and effective as 0.02% drops. Both inhibit membrane function and only these have been shown to have uniform amebicidal activity, providing treatment is maintained for an adequate time.

Treatment with a single drug may result in resistance and combinations of PHMB, or chlorhexidine, and propamidine or neomycin are normally used. Such combinations may consist of two or more of these.9

Antivirals

Acyclovir

Acyclovir (acycloguanosine) interferes with the formation of DNA only in infected cells and blocks its further development. The enzymes involved act selectively as a substrate for viral, but not for cellular, thymidine kinase and therefore has a targeted action that does not affect host cells. It is useful in herpes simplex and herpes zoster infections. Toxicity is low, but occasional superficial punctate keratitis may occur.

Trifluorothymidine (F3T)

Trifluorothymidine (F3T) blocks the synthesis of DNA and is incorporated into viral DNA rendering the virus particle inactive. It is both lipid and water soluble and so penetration is good. It can be used for dendritic and geographic ulcers. It is rarely used, but if prescribed care must be taken to

maintain treatment for at least two weeks or, afte the initial elimination of the virus, the infection will recur and rise to higher levels than previously recorded. It is available as a drop, is very effectiv and has low toxicity.

Under specialist supervision viral ulcers may be treated with antiviral drugs to which cortico steroids may be added at the appropriate time.

ANTI-INFLAMMATORY DRUGS

This is a large group of drugs that includes corti costeroids, nonsteroidal anti-inflammatory drug (NSAIDs), antihistamines, drugs that block hista mine release and antifibrotics.

Corticosteroids

Corticosteroids (steroids) are used in cases o uveitis, iritis, and episcleritis. They reduce inflam mation in postoperative patients and following trauma, but are rarely needed in cases of allergy They should only be used in specialist care and never on the undiagnosed red eye because they can exacerbate infections and may lead to cornea ulceration and even perforation.

Corticosteroids reduce inflammation by inhibiting the release of arachidonic acid, so pre venting the formation of prostaglandins and othe chemical mediators. The chemotaxis of white blood cells and the action of immunocompetent cells ar reduced.

Corticosteroids initially bind to a steroid recep tor in the cell’s cytoplasm. The complex then enter the nucleus where it alters the DNA, and causes change in protein synthesis, which affects the func tion of the cell. In the blood vessels corticosteroid effect changes in the endothelium, reducing capil lary permeability and minimizing the inflamma tory exudate. Corticosteroids reduce scarring by altering the formation of fibroblasts and the deposi tion of collagen. Clinically they reduce pain, red ness, swelling and temperature at the site of action but do not affect the cause of the inflammation.

Corticosteroids can be applied topically, by subconjunctival injection, and are sometimes used systemically. Topical application is usually effec tive in anterior segment disease. They are avail able as drops or ointment

The strongest corticosteroid commercially available is 1% prednisolone acetate (Pred Forte®), which is more effective than prednisolone phosphate (obtainable as 0.5% Predsol® or Minims® Prednisolone). Dexamethasone is longer acting and may need fewer applications. Fluoromethalone (FML®) has a similar action to dexamethasone, but is less likely to raise the intraocular pressure (IOP). Loteprednol etabonate is a newer corticosteroid that has little effect systemically or on the IOP and rapidly changes to an inactive metabolite.10

Adverse effects of corticosteroids

Raised intraocular pressure The most important complication of corticosteroids is their tendency to raise IOP, whatever the route of administration. This does not usually occur until after 2 weeks of treatment, but can occur even months later, so it is important to check the IOP regularly as long as treatment is maintained. If the pressure rises the treatment may be changed to a drug less likely to raise the IOP. The strength of the drug or the frequency of application can be reduced or, in some cases, it may be possible and necessary to continue with the initial treatment under careful supervision. NSAIDs may also be considered. The use of corticosteroids should not be stopped abruptly, but the strength and frequency of the drug should be tapered gradually to prevent rebound effects.

Cataract This can occur with long-term topical instillation of corticosteroids, but is more usually associated with systemic administration. They form as posterior subcapsular opacities, which may necessitate surgical removal.

Nonsteroidal anti-inflammatory drugs

Nonsteroidal anti-inflammatory drugs inhibit the formation of prostaglandins from arachidonic acid and act as anti-inflammatory and analgesic, and antimiotic drugs. Depending on the class of NSAID they inhibit the action of either cyclo-oxygenase or lipo-oxygenase. They may be used to prevent miosis before cataract extraction and to control pain and postoperative inflammation. They have proved effective, with or without a therapeutic contact

lens, for the control of post-photorefractive keratectomy pain, and pain associated with laserassisted in-situ keratomileusis. Their use in this situation can be associated with the development of sterile corneal infiltrates. This must be distinguished from microbial keratitis and is treated with topical corticosteroids.

Diclofenac may be used topically, as a single dose, in postoperative prophylaxis and is approved by the FDA for use in ocular inflammation. It has been found11 to reduce corneal sensitivity and may retard epithelial healing. Its systemic use is contraindicated in those who have a history of asthma or other allergic responses to aspirin. It may cause burning and stinging on instillation.

Ketorolac has similar actions. Ketotifen is an NSAID that acts by calcium antagonism.

Anti-allergy treatment

Mast cell stabilizers

Mast cell stabilizers inhibit the release of inflammatory mediators. They have a slow onset and their full effect is not felt for up to three weeks, and they must be taken regularly to maintain their effect.

Sodium cromoglycate Mast cells contain preformed mediators, which are released as a cascade in an allergic reaction. Sodium cromoglycate blocks the release of these substances because it results in the reduction in the transport of calcium ions across the mast cell membrane. This stabilizes the cell membrane and prevents the rise in intracellular calcium ions that is necessary for degranulation to occur. Symptomatic relief occurs in a few days, but may take several weeks. These drops should not be used in pregnancy or lactating mothers nor in children under four years of age because their effects in these circumstances are unknown.

Lodoxamide Lodoxamide also prevents calcium ion transport. It is much more potent than sodium cromoglycate and is better at stabilizing the cell membrane. The onset is faster, but it still takes several weeks to become fully effective.

Nedocromil Nedocromil is less irritant than Opticrom and can be given twice daily.

Antihistamines

Histamine is released from mast cells, basophils and platelets during acute inflammatory and allergic reactions. It exerts its effect by means of H1, H2 and H3 receptor sites on cell membranes. In the eye, stimulation of H1 receptors causes itching and mild redness. Stimulation of H2 receptors results in increased conjunctival injection, mucus discharge and edema of the eyelids.

Antihistamines for topical use are H1 antagonists and reversibly block the receptor site. They do not prevent the release of histamine. They are used for seasonal and perennial conjunctivitis to reduce swelling, discharge and itch. They may be used in conjunction with mast cell stabilizers, NSAIDs, corticosteroids and oral antihistamines in cases of giant papillary conjunctivitis. They relieve the symptoms more quickly than mast cell stabilizers.

Levocabastine This is a selective H1 antagonist with a rapid onset, and a duration of action of about 4 hours. Drops may be used four times a day for up to 4 weeks in any 1 year. The drops should be discontinued if there is no improvement in 3 days. They should not be prescribed during pregnancy or for those under 9 years of age. If used in combination with a levocabastine nasal spray, drowsiness may occur. Levocabastine drops may cause blurred vision, local urticaria, shortness of breath and headache.

Emedastine Emedastine is a long-acting antihistamine with a duration of 8 hours and a rapid onset. The drops may be used twice daily for SAC. They can cause transient burning and stinging, blurred vision, dry eye, lacrimation, and staining. If corneal infiltrates occur the drops should be discontinued.

Azelatine Azelatine will relieve symptoms in 10–20 minutes and the effect lasts for 12 hours. It can cause mild irritation and some patients notice a bitter taste.

Otrivine Antistin® Otrivine Antistin® contains antazoline sulphate and xylometazoline hydrochloride, which is a sympathomimetic and should be avoided in angle closure. Absorption may cause systemic side-effects. It causes rapid vasoconstriction and relief of itch.

Olopatidine Olopatidine (Opatanol®) antagonize histamine and prevents histamine-induced cytokin production by conjunctival epithelial cells.

OCULAR DECONGESTANTS

Ocular decongestants are often incorporated i preparations containing antihistamines, such a naphazoline or phenyramine. They result in vaso constriction and a white eye, but if used frequentl they may cause rebound vasodilation and con junctival injection.

MYDRIATICS

The autonomic nervous system consists of sympa thetic and parasympathetic nerve supplies Acetylcholine is the transmitter at the ganglia o both systems and parasympathetic end organs Norepinephrine (noradrenaline) is the transmitte at the end organs of the sympathetic nerve supply In the eye the dilator pupillae muscle is supplie by the cervical sympathetic nerve, and the sphinc ter by the parasympathetic supply via the oculo motor nerve (cranial nerve III).

In contact lens practice mydriatics are used:

●to enhance examination of the fundus

●to paralyse accommodation for refraction

●to dilate the pupil and paralyse accommoda tion in uveitis.

Care must be taken to avoid causing angle clos ure glaucoma, but Patel et al.12 found that i screening is performed accurately, using penligh examination and a history of glaucoma as criteria the risk of dilating a potentially occludable angl was less than 1 in 333 subjects in the populatio examined.

Cyclopentolate hydrochloride

Cyclopentolate hydrochloride is available in 0.5% and 1.0% solutions. One drop in each eye, and i necessary repeated after 10 minutes, is used fo refraction. The onset of action is within 30 min utes and the effect lasts less than 24 hours Neurotoxicity can occur in some cases. The refrac tion results will be 0.5 DS more than the nonmy driatic refraction.

Tropicamide

Tropicamide 0.5% and 1.0% is a mydriatic, but with poor cycloplegic qualities. The maximum effect occurs after 25 minutes and recovery starts rapidly thereafter. The effect lasts up to 6 hours. One drop is usually all that is needed for fundoscopy.

Atropine

Atropine 1% is rarely used for refraction, even in children, because the effect lasts up to 2 weeks and is irreversible. Contact dermatitis and toxic systemic effects are not uncommon with atropine.

Systemic side-effects tend to occur more often in the very old or very young. Heavily pigmented eyes are more difficult to dilate than lighter eyes and care should be taken to avoid an overdose.

The British National Formulary advises that driving should be avoided for 1–2 hours after mydriasis because the vision may become blurred, particularly in nonpresbyopic patients.

TOPICAL ANESTHETICS

Topical anesthetics are used for diagnosis and therapeutic purposes. They should never be permitted for domiciliary use because of their toxic effect on the epithelium, and the masking of severe symptoms.

Topical anesthetics block the conduction of nerve impulses by reducing the permeability of the cell membrane to sodium ions. To achieve corneal anesthesia they need to be lipid soluble.

Anesthetics occur in ionized and nonionized forms and this is influenced by the pH of the tissue, the higher the pH the greater the ionization. The anesthetic effect is due to the ionized form. Inflammation lowers pH and reduces the effect. The onset of action is rapid, less than 30 seconds, and the effect is transient with no lasting sequelae. A single drop is all that is necessary, except in surgical cases, for tonometry, gonioscopy, the removal of foreign bodies, or for diagnostic or trial contact lenses.

As with other topical anesthetics it stings on instillation and the patient should be told of this before application. Contact lenses may be re-inserted with care after 20 minutes, but patients

should be warned to avoid dusty, windy environments for the immediate future.

Oxybuprocaine

Oxybuprocaine hydrochloride 0.4% is available unpreserved as Minims® Benoxinate (Chauvin). The onset is within 10 –20 seconds and the duration of action is 10 –20 minutes. There are few sideeffects and allergic reactions are rare.

Amethocaine

Amethocaine is best avoided except for minor surgery because it can be very irritating and is more likely to cause allergic reactions. It has a longer duration of action and produces a more dense anesthesia. It effectively anesthetizes the conjunctiva and peripheral cornea (e.g. for foreign body removal) when Benoxinate does not.

Proxymetacaine

Proxymetacaine (Ophthaine®) causes less stinging and may be preferable, particularly for children and is used by most people for diagnostic procedures. Minims® Proxymetacaine is available with and without fluorescein. It is used in conjunction with amethocaine for interventions and surgery.

Lignocaine

Lignocaine is used for injection into the eyelids for minor surgery and is available topically in combination with fluorescein for tonometry.

Complications of topical anesthetics

Side-effects are rare, but topical anesthetics cause disruption of tight junctions, which results in an increase in corneal epithelial permeability and punctate staining. Overdosing may occur if a patient is given topical anaesthetics to relieve symptoms. It may lead to a central corneal ulcer, infiltrates, stromal edema and iritis. Excessive doses may also be associated with a red eye, and debilitation.

VITAL DYES

Fluorescein

Fluorescein is a vital dye that exhibits fluorescence. This means that it absorbs light at one wavelength (blue) and emits it at another (green). It is available as Minims® Fluorescein Sodium 1% or 2%. It is also marketed in solution with either proxymetacaine or oxybuprocaine. The dye itself is orange, and is best illuminated using a cobalt blue light source. The image can be further enhanced, particularly for photography, by the use of a Wrattan filter. Pseudomonas aeruginosa and adenovirus both grow well in fluorescein drops.13 For this reason most clinicians use strips impregnated with fluorescein or unit dose Minims® drops.

Fluorescein is water soluble and will not normally penetrate the corneal epithelium, so it can be used to outline the tear film and to assess the patency, or otherwise, of the nasolacrimal ducts. It will stain damaged conjunctival epithelium, though not as well as Rose Bengal, and is used for locating areas of the cornea damaged by trauma or disease.

Fluorescein is used in applanation tonometry to demonstrate the correct endpoint, which is when the inner borders of each green crescent overlap.

Fluorescein angiography is undertaken using intravenous fluorescein 5, 10 or 25%, which permits the tracing of the passage of the dye through the choroidal and retinal vessels. It can then be photographed using special filters and a permanent record made of any leakage from blood vessels. Fundus angiography is useful in the diagnosis of vascular disease and retinal neoplasia. Patients may suffer nausea and vomiting, and the skin and urine will fluoresce for some period after the dye has been injected. This investigation should not be undertaken unnecessarily because it has a definite morbidity, and an emergency tray and oxygen should always be available.

Fluorescein is used to assess the fit of rigid contact lenses. Soft lenses have a high water content and the dye is absorbed into the lens, so it is not used in estimating the fit of these lenses. The eye should be well irrigated with copious amounts of normal saline before replacing a lens on an eye that has been stained with fluorescein. If fluorescein

inadvertently does enter a lens the patient can b reassured that it will be removed as the lens i cleaned and soaked.

Rose Bengal

Rose Bengal is derived from fluorescein, but doe not exhibit fluorescence. It stains dead or degener ate cells and is better at staining conjunctiva than cornea, because the contrast is greater. Ros Bengal stains where there is poor cover by the tea film. The effects of meibomian gland diseas can be demonstrated because there is staining inferiorly and superiorly outside the area o exposure. Rose Bengal causes considerable dis comfort on instillation and some clinicians apply a topical anesthetic before the dye, but th discomfort may last longer than the action of th anesthetic.

Lissamine green

Lissamine green is similar to Rose Bengal, but les irritating, but is not available in the UK at the tim of writing.

LUBRICANTS AND WETTING DROPS

The treatment of dry eyes is a common problem in contact lens practice. The more viscous solutions o artificial tears have a longer duration of action Drops such as Viscotears® (CibaVision) contain synthetic high molecular weight polymers o acrylic acid. Hypromellose is an economical and effective treatment, but may need to be used fre quently. It is available in proprietary and nonpro prietary forms and combined with dextran “70” in Tears Naturale®(Alcon). Polyvinyl alcohol is effec tive in some cases as Liquifilm Tears® (Allergan and Sno Tears® (Chauvin) and, combined with macrogol “8000” in Hypotears® (CibaVision). Al these are marketed with preservatives, usually benzalkonium chloride and should not be used in conjunction with soft contact lenses. Hypromellos may be obtained from some hospital pharmacie in an unpreserved form and Minims® market an unpreserved equivalent (hydroxyethylcellulose) Drops such as Refresh® (Allergan), and Focu Clerz® (CibaVision) are also unit dose preparation

and do not contain preservatives, nor does Vislube® (Chemedica). All these may be used with contact lenses. Itoi et al.14 found sodium hyaluronate to be more effective in contact lens wearers with peripheral staining than artificial tears and the subjective symptoms improved.

In patients with very dry eyes more frequent instillation of preservative-free normal saline is often more effective than some thicker drops.

In all cases associated with contact lens wear the fit and type of lens must be reviewed to see if this is a factor, and the lens altered if necessary.

1.German EJ, Hurst MA, Wood D. Eyedrop container delivery: a source of response variation. Opthalmol Physiol Opt 1997;17:196–204.

2.Christensen MT, Barry JR, Turner FD. Five-minute removal of soft lenses prevents most absorption of topical ophthalmic solution. CLAO J 1998;24:227–231.

3.Clinch TE, Hobden JA, Hill JM, et al. Collagen shields containing tobramycin for sustained therapy (24 hours) of experimental Pseudomonas keratitis. CLAO J 1992;18:245–247.

4.Walker S, Draper CJM, Bowman R, et al. Lack of evidence for systemic toxicity following topical chloramphenicol use. Eye 1998;12:875–879.

5.Macasi MS, Goel AK, Michael MM, et al. Deposition of ciprofloxacin, prednisolone phosphate and prednisolone acetate in sequence disposable lenses. CLAO J 1993;19:166–168.

6.Kalayci D, Basci N, Kortuny S, et al. Penetration of topical ciprofloxacin by presoaked medicated soft contact lenses. CLAO J 1999;25:182–184.

7.Friedlander M. Twice a day versus four times a day ofloxacin treatment of external ocular infection. CLAO J 1998;24:48–51.

8.Hope-Ross MW, Chell PB, Kervick GN, et al. Oral tetracycline in the treatment of recurrent corneal erosions. Eye 1994;8:384–388.

9.Seal D, Hay J, Kirkness C, et al. Successful medical therapy of Acanthamoeba keratitis with topical chlorhexidine and propamidine. Eye 1996;10:413–421.

10.Asbell P, Howes J. A double-masked placebocontrolled evaluation of the efficacy and safety of loteprednol etabonate in the treatment of giant papillary conjunctivitis. CLAO J 1997;23: 31–36.

11.Aaragona P, Tripodi G, Spinella R, et al. The effects of topical administration of non-steroidal antiinflammatory drugs on corneal epithelium and corneal sensitivity in normal subjects. Eye 2000;14:206–210.

12.Patel KH, Javi JC, Tielsch JM. The incidence of acute angle-closure glaucoma after pharmacologic mydriasis. Am J Ophthalmol 1995;120: 709–717.

13.Kowalski RP, Romanowski EG, Warkhoun B, Gordon YJ. The survival of adenovirus in multidose bottles of topical fluorescein. Am J Ophthalmol 1998;126:835–836.

14.Itoi M, Kim O, Kimura T, et al. Effect of sodium hyaluronate ophthalmic solution on peripheral staining of rigid contact lens wearers. CLAO J 1995;21:261–264.

CHAPTER CONTENTS

Handwashing 149 Lens care 149 Lens cleaning 150 Disinfection 152

Rinsing solutions 154 Solution bottles 154

Disinfection of contact lenses and tonometers in the consulting room 154

Provision of solutions 155 References 155

All types of lenses accumulate deposits from th tear film, cell debris, cosmetics and microorganism from the atmosphere and from fingers when hand ling the lens. It has been shown that a considerabl percentage of lens wearers never clean their lense before disinfection and many do not use enzym cleaners1 (Fig. 15.1). To minimize the risk of seriou eye infections all lenses, except for one-day dis posable lenses, need to be cleaned and disinfecte daily on removal from the eye, and care system have been designed for RGP and soft lenses.

HANDWASHING

Handwashing is important before any lens hand ling to prevent the addition of organisms to a clea and disinfected lens, and to avoid increasing th load on a lens when removing it from the eye.

Proper handwashing facilities must be avail able in the consulting room, and any areas wher lenses are handled by staff or patients.

It is preferable to use soap such as Simple Soap which does not contain cream or perfume. Anti bacterial liquid soap has been found to reduce bac terial contamination during washing,2 but ma affect the corneal epithelium. Finally hands shoul be dried thoroughly, using a lint-free towel, to pre vent contamination of lenses with tap water.

LENS CARE

All lenses, except those used on a daily basis, o those worn overnight for a month, need to b cleaned, on removal from the eye, and then store

Figure 15.1 Rigid lens with deposits and adherent dried storage solution.

in disinfecting solution. Both these functions can be performed by a single multipurpose solution (MPS). Different solutions are required for RGP and soft lenses because the RGP solutions may contain chemicals that bind to soft lens materials, notably benzalkonium chloride, which may cause a toxic reaction.

All solutions contain buffers that maintain the pH of the solution within the narrow limits suited to lens wear . The active ingredients are the preservatives. These are disinfectants that only kill vegetative organisms and their use does not result in sterilization of the lenses. Deposit formation may be minimized by regular use of an enzyme solution, and RGP lenses may be returned to the laboratory for cleaning and polishing. Solutions may cause an allergic response in some patients (Fig. 15.2).

LENS CLEANING

Lenses are cleaned using a surfactant cleaner or a MPS. Surfactant cleaners contain detergents and soaps, which reduce surface tension. They make oily contaminants easier to remove with friction, and oily debris is emulsified and can be rinsed away. Surfactant molecules can also aggregate to form micelles , which trap contaminants and can be rinsed off.

Mechanical friction by rubbing the lens, filled with cleaning solution, on both surfaces loosens surface debris and microorganisms that are rinsed

Figure 15.2 Allergic response to contact lens solution.

away with normal saline, MPS or disinfecting solution. Tap water should not be used for rinsing lenses because of the risk of introducing Acanthamoeba into the eye. Rubbing, followed by overnight disinfection, has been shown to be more effective than overnight disinfection followed by morning surfactant cleaning, which tends to increase the microbial load because of contaminants added during lens handling.3

Multipurpose solutions are designed to improve lens care compliance, but with no separate cleaning step it is easy for the tired or lazy to omit the cleaning step and just store the lens in the solution (Figs 15.3–15.5).

The advent of “no rub” solutions has apparently reduced the need for mechanical cleaning, but a recent paper by Raali et al.4 in which soft contact lenses were soaked in a variety of solutions, having been previously soaked in solution containing Acanthamoeba trophozoites, showed a decrease to only 10% of the load. I am therefore of the opinion that a rub and rinse step is still worthwhile.

Hydrogen peroxide systems have some intrinsic cleaning ability because surface debris is loosened as the lens parameters alter in the different solutions.

Surfactant cleaners are available with a number of care regimens. Miraflow (CibaVision) uses

Figure 15.3 Contribution of various elements to lens disinfection. From Warner–Lambert Research Institute 1975. Reprinted from Janoff LE. Origin and development of hydrogen peroxide disinfection system. CLAO J 1990;16(1):40.

isopropyl alcohol which is bacteriostatic,5 so prevents the growth of bacteria, and kills amebae (amebecidal)6 and does not contain a preservative. It is useful for patients with particularly greasy tear film.

Cleaning with daily cleaner maintains visual acuity and provides greater comfort than a dirty lens, and has fewer deposits.7

Enzyme cleaners

Enzymes are catalysts for specific reactions and include proteases, lipases and amylases, which break down protein, lipids and polysaccharides respectively, into smaller units that are easier to remove with a rub and rinse step.

Figure 15.4 Lens cleanliness. Percentage of lenses at each visit with no visible or microscopic deposits viewed at 7 to 10 -magnification (Rudko Type 1). Reprinted from Lebow K and Christensen B. Cleaning efficacy and patient comfort: a clinical comparison of two contact len care systems. ICLC 1996;23:89–90, with permission from Elsevier.

Figure 15.5 Lysozyme levels on day 90. HLPC analysis of Durasoft and Hydrasoft lenses. Reprinted from Lebow K and Christensen B. Cleaning efficacy and patient comfort a clinical comparison of two contact lens care systems. ICLC 1996;23:89–90, with permission from Elsevier.

Papain comes from the papaya plant and con tains a protease, so only affects protein. It needs t be well rinsed from the lens or it may cause irrita tion. Subtilisin is manufactured from a bacillu and also contains protease. Pancreatin is derived from animal pancreas and contains protease, lipas and amylase while Amiclair tablets (Abatron contain protease, lipase and pronase from nonani mal sources and also ethylenediaminetetracetat (EDTA), a chelating agent that enhances th