The eye has a range of natural defence systems which very effectively protect the eye's tissues from inflammation and infection. The placement of a contact lens on the eye, however, places an added burden on these systems, which can sometimes result in an adverse response or event.

In practice, being able to recognise and effectively manage adverse events is an important part of our professional responsibilities. Accurate diagnosis enables us to identify possible causes and risks, to decide whether treatment is necessary and gauge the time to resolution, and to inform the patient of the likely time out of lens wear, chance of recurrence, and strategies to reduce risk. In this editorial we will look at typical adverse events that accompany lens wear, what events are occurring with silicone hydrogel lenses, and how these events can be effectively managed.

The high oxygen permeability and other physical features of the new materials, have impacted the incidence of adverse responses seen with silicone hydrogel lenses.

The new highly oxygen permeable silicone hydrogel materials have eliminated physiological changes due to hypoxia. Overnight edema levels are similar to the levels seen with no lens wear and are far lower than those with commercially available disposable soft lenses[1][2]. Microcysts, the main clinical indicator of corneal edema[2]are rarely if ever seen with silicone hydrogel EW (except when initially transferring a low Dk wearer, the "rebound effect", this is the same phenomenon that occurs when some low Dk wearers discontinue lens wear.). We also find remarkably 'white eyes' with silicone hydrogel lens wearers due to the reduction in limbal hyperaemia. 'Ghosting' of neovascularisation in previous wearers of Low Dk EW soft lenses due to emptying of the vessels occurs in silicone hydrogel lens wear[3][4].

It is hypothesised that the increased oxygen permeability of the silicone hydrogel lenses ensures that the eye's defences are not compromised due to a healthier epithelium, providing better protection against infection (Microbial Keratitis).

Studies at CCLRU/CRCERT and CCLR of adverse responses with the new lenses compared to low Dk lenses have shown that there are similar rates of inflammatory conditions but higher rates of some of the mechanically induced adverse events.

While clear identification of an adverse event is essential, unfortunately widespread confusion still exists in the literature and in clinical practice, with either the same adverse reactions being categorised differently or different reactions being labelled as the same type of event. For example, the term 'corneal infiltrate' is used to describe anything from a large infected ulcer to a few cells in the cornea.

Microbial Keratitis (MK) is the only infection related to contact lens wear. All other events are either inflammatory in nature or mechanically induced. The inflammatory events such asCLPU, CLARE, IK, AIKandAImay be associated with the presence of bacteria and their toxins on the eye, the lids or the lens, but are not infective. Infiltrates can occur in response to infection, inflammation and mechanical disturbance to the cornea.

CCLRU and the LV Prasad Eye Institute (LVPEI) in India have conducted numerous clinical contact lens trials in the last 10 years. Detailed information on the signs, symptoms, appearance, laboratory findings, treatment and management of a range of adverse events have been collected. This information resulted in the development of theCCLRU/LVPEI Guide to Corneal Infiltrative Conditions seen in Contact Lens Practice (PDF-2.24MG). This Guide categorises events into serious and symptomatic; clinically significant and commonly symptomatic; and clinically non-significant and asymptomatic.

The CCLRU/LVPEI Guide to Corneal Infiltrative Conditions seen in Contact Lens Practice can now be viewed under the new Resource Section of the Research Library. Copies of the CCLRU/LVPEI Guide to Corneal Infiltrative Conditions seen in Contact Lens Practice can be obtained by contacting CCLRU (k.evans@crcert.unsw.edu.au)

Below is some information about particular adverse events:

- serious and symptomatic

Microbial Keratitis is caused by microbial infection of the cornea, and is classified as a serious adverse event. It is has the potential to result in vision loss, although the reports of cases resulting in vision loss are extremely low.

MK is rare and is the only serious adverse event to occur in contact lens wear.

The presentation of MK can vary depending on the type and virulence of the micro-organism involved, and the stage at which the patient presents. In general, excavation of the corneal epithelium, Bowman's layer and stroma is seen, with serious necrosis and infiltration of the underlying tissue[5]. The shape of the lesion is usually irregular and "satellite" lesions (smaller lesions adjacent to the primary site of infection) may be present. Anterior chamber reaction is often observed in the active stage.

Aetiology:Risk factors such as hypoxia, trauma, ocular surface disease, certain systemic conditions and contact lens wear are known to be associated with the development of MK[6][7][8][9][10].

Treatment:Prompt attention and treatment are mandatory as infection associated with virulent organisms can progress and cause severe destruction of the cornea within 24 hours. Conjunctival swabs and a corneal scrape will help to determine the type of microbe involved. Aggressive antibiotic therapy delivered topically at frequent intervals is then the usual approach, however treatment can vary according to the stage and severity of the condition. Once the microbe has been identified the treatment may be modified based on the sensitivity of the organisms to particular antibiotics.

While MK is rare, significant delay or inappropriate treatment can affect the visual outcome. A conservative approach is therefore recommended with the treatment of any focal infiltrate with significant overlying staining, until the possibility of MK has been eliminated.

Aetiology:CLPU is an inflammatory reaction of the cornea thought to be due to bacteria adhering to the contact lens or toxins released by the bacteria. The cornea is not infected and bacteria is not found on scraping or biopsy of the lesion.

Treatment:In its acute phase CLPU necessitates temporary discontinuation of lens wear until resolution of the corneal infiltrates. No medical therapy is needed. Patients should be monitored until the event resolves. The events always resolve in a characteristic 'bulls-eye' scar. The patients that present to our clinics with healed peripheral circular scars without treatment highlight the self-limiting nature of CLPU events. The condition is prone to recurrence but does not necessitate permanent discontinuation.

CLPU can mimic early MK, however with CLPU the symptoms are milder and begin to recede immediately on discontinuation of lens wear. Again, a conservative approach is recommended however with the treatment of any focal infiltrate with significant overlying staining, until the possibility of MK has been eliminated.

Aetiology:A significant number of lenses recovered from cases of CLARE have been contaminated with Gram negative bacteria. It is thought the reaction is an inflammatory response to the toxins produced by the bacteria.

Treatment:Temporary discontinuation of lens wear until resolution of the corneal infiltrates is required. This may take one to two weeks. As with CLPU, CLARE simply resolves on cessation of lens wear without the need for medical therapy. Patients should be monitored until the event resolves. Approximately one third of the cases recur[11][12], and patients need to be counselled as to the possibility of recurrence before recommencing lens wear.

Aetiology:IK is multifactorial in nature. It may be in response to bacterial toxins, or a trapped foreign body or due to mechanical trauma to the cornea. Mechanical trauma is diagnosed by a positive history and or/an epithelial defect suggestive of trauma.

Treatment:Lens wear should be suspended, and patients monitored until the event resolves. Prophylactic antibiotics can be prescribed if there is any loss of epithelium.

Aetiology:The aeitiology is uncertain, but it has been hypothesised that it is a hypersensitivity reaction, either delayed[14]or immediate[15][16]. It is believed that lens deposits such as protein is the major risk factor[17][18][19]. Lower patient age[20], increased periods of lens wear[18], infrequent replacement of lenses[18]and the wear of larger lenses[18]have also been suggested as risk factors. Mechanical irritation due to front surface deposition may also play a role.

Treatment:Management options for General CLPC include frequent cleaning and replacement of lenses to reduce deposits, a decrease in wear time, or a change in mode of wear (EW to DW), lens type or material. Mast cell inhibitors in conjunction with steroids are used in some cases to manage recurrent events. Tarsal redness decreases significantly, but does not tend to return to baseline levels, despite successful management. Papillae also may remain dispersed over the entire tarsus, but are significantly smaller.

Aetiology:Local enlarged papillae are also found in patients with sutures, ocular prostheses etc, suggesting that mechanical trauma has a role in the aetiology of local CLPC[13].

Treatment:Following discontinuation of lens wear, the tarsal redness usually resolves in 2-4weeks, however the papillae, while smaller, tend to remain. Localised CLPC has a tendency to recur in approximately 50% of cases[13]and following a second episode in the one eye, current management strategy is to change to frequent replacement low Dk daily wear or daily disposable lens wear, which is usually successful. Refitting with a steeper base curve may be beneficial for some patients.

Aetiology:SEALs have a multifactorial aetiology. Identified risk factors include: steep corneas, tight eyelids, Asian eye shape, presbyopia and male gender. Current findings of poor wettability and tight fitting lenses in silicone hydrogel EW SEALs cases, support the hypothesis that mechanical chaffing due to a thinning tear film in the superior cornea are factors in the development of SEALs.

Treatment:Discontinuation of lens wear until resolution of the SEAL, including infiltrates, is recommended. Resolution usually occurs within 24-48 hours, but may take 1-2 days longer if infiltrates are present. SEALs tend to recur in approximately 50% of cases, but the time to recur varies widely among patients. There is usually no scarring on resolution or after repeated events.

Treatment:If the erosion is small (<0.5mm) and superficial, lens wear should be discontinued for 12-24 hours and the patient should be monitored. For large (>0.5mm) superficial or deep erosions, lens wear should be discontinued for at least 24 hours and not resumed until complete resolution. It is important not to patch the eye as this significantly increases the risk of secondary infection[23]. Prophylactic antibiotics may be used in severe cases, however preservatives in these solutions can delay healing. Artificial tears can be used if discomfort is present.

Treatment:Discontinuation of lens wear in AIK is usually recommended until the redness and/or staining has resolved, which usually takes a couple of days. If there are a small number of focal or only slight diffuse infiltrates and no staining or redness, lens wear can be safely maintained.

Aetiology:VK is an immune response of the cornea, caused by various strains of adenovirus.
Treatment:Lens wear should be discontinued for the course of the infection, which generally lasts for several weeks. Some VK can be very contagious and caution should be exercised with hygiene. A topical antibiotic can prevent an opportunistic, superimposed bacterial infection.

The adverse events seen in silicone hydrogel practice are also seen in other modes of wear. The procedures for silicone hydrogel patient education and management should therefore be no different to other contact lens practice.

Patients should be educated and regularly reminded that they should contact an eyecare practitioner immediately upon noticing symptoms. Patients should also be taught how to avoid risks with their contact lens wear. Most importantly, they should check every day whether their eyes look good, feel good, and see well; and they should never wear a lens overnight if it is uncomfortable or if they are unwell. All contact patients should have an up to date pair of spectacles, should an adverse event necessitate temporary discontinuation of wear.

Practitioners should ensure that they are familiar with the signs, symptoms and management of the various types of adverse event seen in contact lens wear, and have systems in place to provide immediate care to any patient who suspects an adverse event. With practitioner and patient education, adverse events can be managed easily and effectively leading to increased patient confidence.