Le eye infections arise when pathogenic microorganismswhich may be bacteria, fungi or viruses, invade any part of the eyeball or the surrounding area.
What is an infection
Infection is a physiological process caused by the entry and multiplication of microorganisms in the tissues of a host. Infectious disease is the manifestation of infection.
Depending on the type of micro-organisminfection can be: bacterial, viral, fungal, from protozoa. When the infectious agent comes from the external environment, we speak of exogenous infectionWhen, on the other hand, it is already present in the body (on the skin, in the oral cavity, in the gastrointestinal or genitourinary tract) as a harmless commensal (host) before becoming harmful, one speaks of endogenous infection.
Micro-organisms can enter the body by different routes and in different ways. If they are not immediately neutralised by the body's defensive immune system, some micro-organisms can survive without causing damage in what is termed 'subclinical infection', i.e. a condition of latency, or, after an incubation period in which they settle and multiply, they can cause an 'acute' infection, which develops rapidly, or if it persists over time and does not heal completely, it can become a 'chronic' infection.
The infection may remain localised at the point of entry of the micro-organism or it may pass into the bloodstream temporarily, leading to 'bacteremia' or cause a serious impairment of general health in the case of 'sepsis'.
When pathogenic micro-organisms reach the ocular apparatus or penetrate it directly, 'eye infections' result.
eye infection
Areas that can be affected by eye infections include, first of all, the frontal surface of the eye: the cornea.
The cornea is a transparent membrane, devoid of vessels, but rich in nerve fibres. The cornea is continuously wetted by the tear film that adheres to its surface. The tear film-corneal surface interface constitutes the most powerful converging lens in the human eye.
The cornea is about 1 mm thick and consists of five layers from outside to inside:
- a pavimentous (stratified) epithelium,
- Bowman's membrane,
- the stroma,
- Descemet's membrane,
- the endothelium.
The stability of the tear film and the transparency of the cornea are essential for vision. Behind the cornea lies the anterior chamber, which is filled with a clear fluid called aqueous humour.
Eye infections often affect the conjunctiva.
The conjunctiva is a thin membrane that covers, like a mucous membrane, the anterior portion of the eyeball, with the exception of the cornea. The conjunctiva is reflected in the fornices upper and lower conjunctival sac on the inner face of the eyelid and reaches the eyelid margin. This forms a conjunctival pouch (conjunctival sac) underneath the upper and lower eyelid that provides a plane for the movement of the eyeball. The conjunctiva contains numerous mucus-secreting cells. Their secretion forms the innermost layer of the tear film. In contrast to the sclera, which is whitish and rather thick, the conjunctiva is almost completely transparent, but well vascularised.
Management of eye infections
There are many different types of eye infections, and it is crucial in each individual case to identify the particular type of eye infection in order to resort to the appropriate treatment.
Eye infections, if left untreated, can damage eye structures leading to low vision and, in the most serious cases, blindness. Even if the eye is protected by the continuous flow of tears, which contain molecules with antibacterial action, the infection and inflammation, once established, may not resolve spontaneously and in these cases require immediate management.
What does an infected eye look like?
Symptoms of eye infections may include:
-red eyes
-pain
-excessive tearing or dry eyes
-light sensitivity
-swelling of or around the eyes
-burning
-blurred vision
Whenever you suspect an eye infection, you should always consult your ophthalmologist for a thorough examination. Attempting to self-diagnose your condition can delay effective treatment and potentially damage your eyesight.
How can an eye infection be identified?
Your ophthalmologist can take a sample from the affected area of the eye to perform a "bacterial culture" in order to assess the exact type of infectionwhere this exists. This is also important to determine the most effective treatment, i.e. to identify the antibiotic that most selectively targets the type of bacteria that is triggering the infection.
Eye infections: the ones you need to know about
Conjunctivitis
La conjunctivitisa common, highly contagious eye infection that often spreads among children in kindergartens, classrooms and similar environments. Teachers are also more exposed to conjunctivitis as they work in close contact with young children. The most common types of infectious conjunctivitis are viral or bacterial in origin. Infants can also contract conjunctival eye infections (gonococcal and chlamydial conjunctivitis) during childbirth if the mother has a sexually transmitted disease.
Ophthalmic herpes
L'herpes ocular arises following exposure to the virus herpes simplex.
Primary herpetic infection usually occurs in childhood and is often asymptomatic. The route of entry of the virus is through the skin or mucous membranes. Once it has entered, the herpes virus settles in a latent state in the trigeminal ganglion, cervical, sympathetic and possibly also in the stem cells of the corneal epithelium.
Multiple stimuli, even trivial ones, can subsequently lead to reactivation of the virus and result in the clinical manifestation of herpetic keratitis.
It would be more correct to speak of corneal herpetic disease rather than herpetic keratitis because the virus can give rise to different corneal manifestations, differing in mode of presentation, but above all in pathogenesis. This point is of fundamental importance in clinical practice because the treatment is different, depending on whether the manifestation is infectious, inflammatory or dystrophic.
Acanthamoeba keratitis
Keratitis by Acanthamoeba is a serious eye infection that is extremely difficult to treat and can lead to blindness. L'Acanthamoeba is a genus of free-living amoeba found in soil and water. It is also frequently found in tap water, and transmission of the parasite through the incorrect use of contact lenses is one of the main causes of AK infection in Western countries, so much so that it has prompted the organisation of many educational campaigns to inform contact lens wearers about the proper hygiene of these devices.
L'Acanthamoeba pcan enter the eye either as a result of direct contact with contaminated tap water, but also through wet hands, or due to the use of an ineffective multipurpose solution to disinfect against the parasite. Data indicate that cases of AK are on the rise and some outbreaks have been recorded in recent years, often related to low disinfectant power of products used for contact lens care.
Contact lens wearers are at increased risk of contracting parasites that can invade the eye and cause this serious infection. This is why contact lens wearers should observe certain hygiene and safety tips, e.g. avoid swimming while wearing contact lenses and ensure cleaning and disinfection with appropriate products to minimise the risk of eye infection.
Endophthalmitis
Endophthalmitis is a type of infection that can occur as a result of an eye-penetrating injury or as a fortunately uncommon complication of eye surgery such as cataract surgery. Whenever the eyeball is significantly penetrated and injured, there is a 4-8% risk of endophthalmitis.
Fungal keratitis
La fungal keratitis, often associated with fungi of the genus Fusarium, which are commonly found in nature. This and other fungi can invade the eye, for example, through a penetrating wound.
Teweldemedhin M et al. Bacterial profile of ocular infections: a systematic review.
BMC Ophthalmol. 2017 Nov 25;17(1):212.
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