The Risk of Contact Lens Wear and the Avoidance of Complications

Contact lenses are lenses placed on the surface of the cornea to correct refractive errors such as myopia (short-sightedness), hypermetropia (far-sightedness) and astigmatism. Lens-related complications are becoming a greater health concern as increasing number of individuals are using them as an alternative to spectacles. Contact lenses alter the natural ocular environment and reduce the efficacy of the innate defences. Although many complications are minor, microbial keratitis is potentially blinding and suspected cases should be rapidly diagnosed and referred to an ophthalmologist for treatment. Several risk factors have been identified with extended wear, poor hand hygiene, inadequate lens and lens-case care being the most significant. Promotion of good contact lens hygiene and practices are essential to reduce the adverse effects of contact lens wear.


Introduction
Ametropic disorders of vision affect between 800 million to 2.3 billion individuals globally. 1Around 140 million users worldwide, including 3.3 million in the United Kingdom, wear contact lenses for the correction of refractive errors. 2,3he British contact lens market value has risen from £33 million in 1992 to £198 million in 2009. 3They are becoming increasing popular because of the clearer vision achieved, for cosmetic reasons, for sports and convenience.Contact lenses are, however a medical device and wearing contact lenses incurs risks with an estimated 6% of users developing complications. 4We will discuss the pathophysiology of contact lens-associated complications and their avoidance.

Search strategy and selection criteria
Soft contact lenses are the focus of this paper.In depth discussion on other types of lenses such as rigid gas permeable, PMMA lenses were out of the scope of this paper.We identified the papers in this review by a computerised search of the Pub-Med database using the queries "contact lens complications" and "contact lens keratitis".We gathered other information from contact lens manufacturers' data sheets and used evidence from published abstracts, major international scientific meetings and textbooks as well as reference collections.
only involved in generalised irritation but also contributory towards complications such as giant papillary conjunctivitis (GPC), contact lens-induced acute red eye (CLARE), contact lens-related peripheral ulcer (CLPU) and infiltrative keratitis (IK) (Figure 1). 10,16,17ditionally, the innate humoral ocular defence mechanisms are reduced by the contact lens limiting tear exchange as well as altering the quantity and quality of the tear film. 2,18The lens interferes with the protective function of the mucin layer (resistant to bacteria adherence) and it hinders the release of anti-microbial factors. 2,8,19,20Coupled with reduced blinking, these ultimately augment the retention of potential pathogens onto the ocular surface facilitating infection. 2

The contact lens directly impedes oxygen transmission
Contact lenses cause micro-trauma attributed to hypoxia.The cornea receives oxygen fundamental to cellular function primarily through the atmosphere and a small quantity from the limbal and aqueous vasculature. 10poxia causes oedema, altering the epithelial and endothelial morphology predisposing the cornea to cellular breakdown. 10,21Reduced oxygen permeability correlates with diminished corneal sensation and increased risk of keratitis.The greater oxygen permeable silicone hydrogel lenses have a five-fold reduced risk of severe keratitis compared with hydrogels. 7arce distribution of oxygenated tear film due to reduced blinking whilst users are performing visual tasks like wor- A. Giant Papillary Conjunctivitis: Delayed hypersensitivity inflammatory reaction due to repeated mechanical irritation to residue on lens surface or toxic reaction to cleaning solutions, characterised by papillary changes in the tarsal conjunctiva (cobblestone appearance), itchiness and reduces lens tolerance. 10,* B. Microbial Keratitis: Cornea infection by bacteria, protozoa or fungus, characterised by excavation of the corneal epithelium with infiltration, odeama, necrosis and neovascularisation.There is significant pain, discharge, photophobia and reduced visual acuity. 9,10,† C. Contact Lens Induced Peripheral Ulcer: Corneal inflammation characterised by a small circular full thickness epithelial lesion and infiltration. 9,† D. Contact Lens-Associated Red Eye: Inflammatory reaction of the cornea and the conjunctiva to toxins produced by bacteria on lens surface particularly in those over wearing or sleeping in lenses.It is associated with severe hyperemia, pain and corneal infiltration (indicated by arrow) with minimal or no epithelial involvement. 9,† E. Infiltrative Keratitis (IK)-Inflammatory process charactersised by corneal infiltration (indicate by arrow). 28,† * Adapted with permission from emedicine.com,2011.Available at: http://emedicine.medscape.com/article/1228681-overview.

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† Adapted with permission from the Guide to Corneal Infiltrative Conditions from the Brien Holden Vision Institute, Sydney, Australia, 2011.To obtain a full scale copy of the Guide, please contact the Brien Holden Vision Institute via http://www.brienholdenvision.org.

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king at computers for a prolonged period can also lessen the oxygen availability. 22Closing of the eyelid, for example, when sleeping is also known to lower the amount of oxygen reaching the tear film causing the cornea to swell. 23Sleeping in lenses may lead to nocturnal hypoxia and deposits may build up on lenses fostering a risk of infection.There is an eight-fold increased incidence of corneal infiltrative events and four-fold increased risk of microbial keratitis in those who sleep wearing lenses compared with users of waking hours only. 24,25ute hypoxia can lead to overwear syndrome whilst chronic hypoxia can instigate corneal neovascularisation contributing to decreased visual acuity, particularly if the central visual axis is involved. 10,22However, with the availability of more permeable lenses such problems have been reduced. 8

Contact lenses introduce pathogens
The corneal surface is under a constant threat of infection from a barrage of pathogens and at any instance up to 63% of contact lenses yield a positive culture consisting of normal commensals. 26Reduced efficacy of the defence mechanisms coupled with change in the concentration and variety of bacteria can contribute towards pathogenic processes. 8With the natural barriers threatened, damage to the intact cornea allows bacteria to adhere to the cell membrane; a vital step in the infectious process as it aids colonisation. 13Recent research has shown there is upregulation of surface-binding receptors further augmenting bacterial adherence. 20Contact lenses, particularly soft non-silicone hydrogel lenses, potentiate their infiltration by inducing changes in corneal epithelium (e.g.reduced desquamation and mitotic activity) making it thinner and increasing the risk of infection. 2,20though a variety of organisms have been isolated from corneal infections, gram negative infections are most common and sight threatening. 9,27,28Infectious keratitis arising due to the ubiquitous Pseudomonas aeruginosa has the greatest associated morbidity. 29This is attributed to a large number of genes dedicated to virulence regulation, environmental adaption and resistance to antimicrobial drugs (e.g.aminoglycosides). 2,30Although rare, 5% of contact lensrelated microbial keratitis is attributed to Acanthamoeba. 31his opportunistic pathogen is found in soil and air; but the main perpetrator is contaminated water (e.g.3][34] Acanthamoeba exists in two forms; a feeding and replicating trophozite which can form antimicrobial-resistant dormant cysts. 32,332][33][34] More recently, early diagnostic techniques and timely treatment with anti-amoebics have improved prognosis; 90% of patient retain visual acuity of 6/12 or better and less than 2% become blind. 34rrectly differentiating microbial keratitis from the less serious sterile corneal infiltrates is crucial. 35Sterile infiltrates tend to be present on the periphery and may be symptomatic or asymptomatic. 28They may be the consequence of lens wear itself, from bacterial endotoxins present in conditions such as Staphylococcus aureus-associated blepharitis, or an amalgamation of the two. 10,36Insults from corneal infiltrates is thought be an aetiological factor in CLPU, CLARE and, IK. 28 Efron and colleagues have suggested that such inflammatory events can either develop or potentiate the risk of microbial keratitis. 28

What are the risk factors for developing contact lens wear complications?
There are a range of modifiable and non-modifiable risk factors involved in the development of complications. 9Nonmodifiable risk factors are younger age (<25 years), older age (> 50 years), male gender, diabetes mellitus, low socioeconomic class and late winter months. 6,8,9,28,37,38Modifiable risk factors are those which can be influenced or altered and includes improper lens and case care, poor hand hygiene, smoking, swimming and showering wearing lenses, as well as extended and overnight wear.Extended wear hydrogel 96 99 Extended wear silicon hydrogel 20 48 Table 1.Incidence of contact lens-associated complications. 7Regular review by contact lens provider

Non-Compliance
Dissenting behaviour amongst contact lens wearers is paramount when considering the main reason for complications. 39A large well conducted study undertaken on behalf of Bausch & Lomb across Europe highlighted that 98% of all lens wearers were non-compliant in at least one aspect of their lens-care regime (Figure 2). 8,40,41) Hand Hygiene: Although inadequate handwashing before lens handling has been associated with a significant increase in risk of infection, the effect is not instantaneous as it takes weeks to remove micro-organisms embedded on the hands. 8,42Perhaps as Morgan suggested, formal training should be provided as this has proven to improve infection control in hospital settings. 8) Care Regime & Solutions: One in three lens-related complications arise arise directly from inadequate lens care. 35,43leaning regimes are either hydrogen peroxide or multipurpose solution based.Multipurpose solution, dubbed as the 'no rub' solution is the most widely used.However, rubbing and rinsing is an imperative step as it removes up to 99.9% of bacteria, thereby adding a safety margin of up to 100,000 times. 8,35Interestingly, recent studies have demonstrated, hydrogen peroxide based cleaning regimes have superior disinfecting capabilities than using multipurpose solution alone. 20,44They reduce the risk of corneal inflammation by ten-fold and disinfects against amoebic cysts. 45,46However, for maximal benefit lenses must be exposed to the peroxide solution for a longer time and must be neutralised before wear to avoid ocular toxicity. 35,47,48) Personal Habits: Other unsafe practises include using lenses beyond their recommended replacement schedule, inadequate lens-case care and topping up contaminated solution. 8,35,49The risk increases four-fold compared with appropriately discarded lenses. 8

Unsupervised wear
Another recent social trend was the use of zero-powered or plano tinted cosmetic lenses designed to change the colour of the eye.They were being bought from unlicensed vendors over the internet without prescription, proper fitting, inadequate information on use, hygiene and complications and no ongoing supervision. 50Complications associated with the use of such lenses were first reported in 2003. 51In 2005, further cases reported users sharing lenses between multiple wearers without adequate cleaning. 52Subsequently, in 2006, Food and Drug Administration (FDA) introduced guidance in the USA, whereby plano lenses could only be purchased under the supervision of a registered practitioner. 53

Orthokeratology
Orthokeratology is the practice of temporary reduction in myopia by the programmed application of rigid gas-permeable contact lenses, usually at night whilst sleeping. 54 late, there has been a resurgence of this phenomenon particularly in East Asia and there are growing concerns about the risk of microbial keratitis and loss of vision. 2,34,55indings of fifty case studies showed 30% had Acanthamoeba keratitis from nocturnal orthokeratology compared with 5% from regular lens wear. 56at are the implications?
Each year 0.02% to 0.04% of lens wearers can lose up to two lines of best correct visual acuity measured using the snellen chart. 24,57As well as the risk of losing sight, other significant morbidity associated includes hospital admission and/or intensive treatment, cost of therapy, visiting a health care provider, taking time off from work and inability to wear lenses. 28,29An Australian study estimated the median direct costs at Aus $760 [interquartile range $1859] and indirect median costs at Aus $468 [interquartile range $1810]. 29Not to mention, patients may claim compensation for negligence. 58

Education
Patient education, particularly regarding the handling and maintenance of contact lenses, is vital in improving overall The International Journal of Medical Students

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compliance. 59There is no statistically significant difference between patients receiving both verbal and written instructions and those receiving oral only. 39However, intense initial education has shown improvements in handwashing. 60rgan and colleagues reported that although, 88% were given lens care information, 23% were unable to recollect seeing any information regarding the risks and complications associated with lens wear. 41Thus, the practitioner must ensure the patient understands the associated risks, how these are best avoided, as well as early recognition of the signs and symptoms and how to proceed in an emergency. 10,61degree of non-compliance will always be present despite education. 61A small study amongst medical students in Malaysia showed that although 88% were aware of complications, only 84% were fully compliant with hygiene and lens-care, and 14% continued use despite experiencing eye symptoms. 62 help the practitioners identify individuals with poor compliance Morgan has developed the "Traffic Light Model" (Figure 3). 8,40,41Green behaviour is equated to a fully compliant user whilst the red behaviour user is considered noncompliant. 8To maximize compliance both verbal and written information should be given and key aspects reinforced during follow-ups. 61Any literature disseminated should be clearly illustrated with sequential steps. 61Table 2 highlights some key aspects that should be reinforced.

Public awareness
Bausch & Lomb launched a novel and invigorating online campaign "Eyegiene" to promote the importance of maintaining good eye health and aid compliance.Their website (http://www.thinkeyegiene.com)features a multilingual virtual optician.Patients can further enhance their knowledge by playing 'Defeat the Enemy,' a game modelled after the Space Invaders, where users combat the virtual bacteria using multipurpose ReNu® solution.To optimise eye care whilst travelling, "On-The-Go-Flight-Pack" was also introduced. 63Such programmes help publicise good lens care to a wider audience.

Conclusion
Contact lens-associated complications can range from selflimiting to potentially sight-threatening, yet they are avoidable.The eye has various defense mechanisms to protect itself; however, the presence of contact lenses alters the natural environment increasing the risk of infection.The incidence of adverse effects of contact lens wear can be reduced by promoting good contact lens hygiene and practices.

Figure 1 .
Figure 1.Contact lens-associated complications A

Figure 2 .
Figure 2. Relative risks and non-compliance for a range of compliance and usage factors

2. Take hygiene instructions seriously 3 .
Follow and understand the care protocol and regime 4. Avoid overnight wear unless extended wear lenses 5. Never shower or swim wearing contact lenses