Le contact lenses (LAC) are the solution increasingly adopted by those who need corrective eye lenses.
In fact, LACs are often preferred to spectacles because they are less bulky, more practical to handle, and above all because they are not visible. However, the prolonged and, above all, incorrect use of LACs can lead to a number of complications, such as dry eye syndrome or the microbial keratitis (CM), one of the most severe and sight-threatening complications. In order to avoid, or at least reduce, the risk of occurrence of disorders related to the use of LACs, one should, in fact, adopt good practices of ocular hygiene especially in order to prevent any microbial infections which can eventually lead to microbial keratitis.
Epidemiology
Microbial keratitis including the bacterial keratitis, fungal and from Acanthamoeba, affect the cornea, leading to inflammatory processes. The causes behind their occurrence can be varied, but the trauma mechanical is often the main cause. Epidemiological studies have shown that the incidence of microbial keratitis varies both according to the pathogen responsible for the infection and according to the type of contact lens used: the use of night-time LACs, for example, compared to daily LACs, is correlated with a higher risk of CM occurrence.
Causes
Under normal physiological conditions, the corneal surface is protected from microbial infection by several protective mechanisms; among these is the tear fluid, which, thanks to the secretion of two molecules, lactoferrin and lysozyme, performs an important antimicrobial function. In addition, thecorneal epithelium constitutes a true physical barrier, which is able to prevent the entry of microorganisms. However, as a result of mechanical trauma or incorrect contact lens wear, the body's natural defences can be compromised and the eyes, in this case, become more susceptible to microbial infection.
Risk factors
The risk factors underlying the onset of microbial keratitis are many and often non-modifiable, such as male gender, genetic predisposition and socio-economic status. Others, on the other hand, depend on certain bad habits or improper ocular hygiene practices, so they can be modified to reduce the likelihood of the onset of the disease itself. Modifiable risk factors include, for example, the prolonged use of Night LACs, smoking, cleansing of LACs with unsuitable solutions or failure to wash hands before use are among the most common. Furthermore, clinical data have shown that the use of aesthetic contact lenses, such as those used to obtain an eye colour different from one's own, can be the cause of microbial keratitis.
Symptoms and signs
The symptomatological picture varies depending on the pathological agent responsible for the keratitis (bacterial, fungal or from Acanthamoeba). In general, the symptoms associated with bacterial keratitis occur immediately and include photophobia (hypersensitivity to light), pain and eyelid swelling; if, on the other hand, one is faced with a fungal keratitis, the symptoms occur 5-10 days after infection, as fungi take longer to grow than bacterial species. The clinical signs in this case in turn depend on the fungal agent responsible for the infection: infections by Candida cause inflammation of the corneal epithelium with 'round' edges; if, on the other hand, it is Aspergillus, the edges of the corneal epithelium will be 'feathered'. Finally, the clinical signs of keratitis by Acanthamoeba are ring-shaped infiltrates and perineuritis, which, however, may also be absent.
Treatment
The treatment depends on the type of keratitis and is determined by the medical specialist following a careful evaluation of the patient's clinical picture. In general, therapeutic intervention strategies include the administration of antibiotic, antifungal and anti-inflammatory drugs.
 Source
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Dr. Carmelo Chines
Direttore responsabile
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