Eye infections

• ANATOMY OR SYSTEM AFFECTED: Eyes, vision

Definition

Eyes are made up of different structures, and all are at risk of an attack from a range of bacteria, viruses, parasites, or fungi that can lead to inflammation and infection. Eye infections are usually diagnosed and described by the specific part of the eye involved or by the mechanism causing the infection. Mismanaged or unresolved eye infections are among the leading causes of blindness around the world. The most frequently occurring eye infection is infectious conjunctivitis, often called pinkeye, which is an inflammation of the conjunctiva, the mucous membrane that lines the eyelids. Conjunctivitis can be further classified as bacterial, viral, or fungal.

The eye is made up of a series of complex structures. Some common infections of the eye structures are blepharitis, an inflammation of the eyelid margins; scleritis, an infection of the sclera, the white outside-covering of the eyeball; iritis, inflammation of the iris, the colored part of the eye; keratitis, inflammation of the cornea, the transparent part of the sclera at the very front of the eye that covers the lens and iris; vitritis, an infection of the liquid inside the eye; chorioretinitis, an inflammation of the retina and its blood vessels; and endophthalmitis, serious inflammation of the inside of the eye.

Causes

No specific pathogen is responsible for infecting the eyes. The human body includes a normal amount of bacteria and is exposed daily to viruses, fungi, and parasites that can cause eye infection and irritation. The most common eye infection is conjunctivitis, caused by adenovirus, a virus of the common cold. In a small number of individuals who contract COVID-19, the SARS-CoV-2 virus can damage the retina and impair vision. There are also more than sixty types of fungi that can lead to eye infection, including aspergillus, candida, and fusarium. Leading eye infections are described in the following sections.

Keratitis. Injury to the eye, a weakened immune system, or a lack of oxygen from contact lens wear allows bacteria, fungi, or parasites to penetrate the cornea, causing keratitis. Most cases of bacterial keratitis are caused by Staphylococcus, which is found in the normal bacteria in the eyelids, skin, mouth, and nose of more than 20 percent of humans, or by Streptococcus, which is the same bacteria that causes strep throat and is normally found in the mouth, skin, intestine, and upper respiratory tract. This type of corneal infection can occur when the eye comes in contact with a contaminated object or person or if a person is already a carrier of Staphylococcus or Streptococcus and self-infects by touching their own eye.

Conjunctivitis. Chlamydia and gonorrhea are common sexually transmitted infections that can cause conjunctivitis. The infection can be transmitted to the eyes through direct contact with genital fluids or through people touching or rubbing their eyes after touching infected genital areas. These infections usually result in conjunctivitis; however, some bacteria, such as Neisseria gonorrhoeae, can penetrate the protective layers of the eye and cause inner eye infection and serious damage. Newborn babies whose mothers have chlamydia or gonorrhea are at high risk for developing severe eye infection.

Herpes simplex virus infection. The herpes simplex virus, which causes cold sores, can also infect the eye, leading to ulcers on the cornea. Recurring herpes infection in the eye can cause major destruction of retinal vessels, leading to vision damage. Chronic herpes simplex infections in the eye will cause some vision loss in 15 to 40 percent of people who have the virus.

Herpes zoster virus infection. Herpes zoster is a virus that causes chickenpox and can be reactivated, causing shingles later in life. Eye infections often occur when the eyes are touched after a chickenpox or shingles lesion has been touched. Like ocular infection by the herpes simplex virus, herpes zoster can also cause corneal ulcers and can lead to retinal tissue damage.

Histoplasmosis. Histoplasmosis is a fungal infection of the lungs, which is caused by the inhalation of spores. These fungal spores can travel through the body to the inside of the eyes, causing ocular histoplasmosis syndrome. This migration may take years or even decades. The fungal infection can cause damage to the retina and, more specifically, to the macula, leading to reduced central vision, similar to macular degeneration. Histoplasmosis frequently occurs in river valleys worldwide. Most people infected with histoplasmosis have no symptoms, but some develop ocular histoplasmosis syndrome. However, histoplasmosis remains a significant infectious cause of legal blindness for Americans between twenty and forty.

Endophthalmitis. Endophthalmitis is a serious infection of the inside of the eye that could lead to blindness. All intraocular eye surgeries, such as cataract surgery or injectable treatments for age-related macular degeneration, carry a risk for endophthalmitis. Typically, the microbial organisms normally found on the patient’s skin or conjunctiva are transferred into the eye cavity during the surgical procedure; contaminated surgical instruments may also be a cause. Once the organisms are inside the eye cavity, inflammation starts to occur, usually reaching serious levels within about six weeks of the original surgical procedure. Other causes may be trauma or be bloodstream-related because of an infection in another part of the body.

Acanthamoeba infection. Acanthamoeba is a single-celled ameba that is commonly found in water and soil. Before contact lens use was common, infection from Acanthamoeba was quite rare. Washing contact lenses with tap water or using a homemade saline solution allows the ameba to adhere to the lens and wait for an opportunity to invade the eye. A tiny scratch or abrasion on the surface of the eye will provide ample opportunity for the ameba to get inside the cornea, multiply, and cause a painful destructive infection called acanthamoeba keratitis.

Trachoma. Trachoma is a chronic and extremely contagious form of conjunctivitis caused by the microorganism Chlamydia trachomatis. It is a leading cause of blindness around the world, most prevalent in developing countries or in disadvantaged populations. If the inflammation persists and is left untreated, the eyelid may turn inward, causing the eyelashes to rub on the surface of the eye and leading to the formation of painful scar tissue, resulting in irreversible blindness.

Cellulitis. Cellulitis is a serious skin infection that can affect the tissues surrounding the eye. It is caused most usually by a spread of infection from an adjacent facial wound, eyelid trauma, insect bite, sinusitis, or tooth infection.

Risk Factors

Eyes are frequently exposed to potential pathogens, therefore making them vulnerable to infection. Certain diseases, behaviors, and environments can increase the risk for these infections. Quite often, an eye infection accompanies another infection, disease, or health condition in the body.

One of the greatest risk factors for eye infection is contact lens wear. Normal contact lens wear that carefully follows the recommendations for care and cleaning does not pose a significant risk. Prolonged wear and inadequate cleaning limit oxygen exposure to the eye and expose the eye to harmful bacteria for extended periods. Smoking when wearing contact lenses increases this risk, as the smoke dries and irritates the surface of the eye. Studies have shown that prolonged lens wear and sleeping with lenses in the eyes increase the risk of infection more than fivefold and can potentially cause permanent vision loss. If an eye infection does occur, contact lenses must not be worn until the infection has completely resolved because the contact lens can cause reinfection.

Contact lens wearers can lower their risk of contracting acanthamoeba keratitis by never allowing their lenses or cases to come in contact with tap water and never wearing contacts when showering or swimming, even in chlorinated pools.

Exposure to ultraviolet light can damage the surface of the eye, making it more susceptible to infection. Proper eyewear outdoors or in tanning facilities is strongly recommended.

A weakened or compromised immune system can lead to an increased risk of infection in the eye and elsewhere in the body.

Patients having any type of intraocular surgery are at an increased risk for endophthalmitis or other infections inside the eye. Common intraocular procedures include cataract surgery and injectable treatments for age-related macular degeneration.

Previous skin wounds or infections, or a sinus or tooth infection, may put patients at an increased risk for orbital cellulitis.

Individuals with substance use disorder who abuse opioids are more likely to contract the rare, serious eye infection called endogenous endophthalmitis.

Symptoms

Symptoms that occur when an infection is present on one of the outer surfaces of the eye, such as the conjunctiva or cornea, include redness and itching, excessive tear production, light sensitivity, mucus-like discharge, eyelid swelling, pain, and involuntary blinking. A symptom of a serious infection, such as cellulitis, includes proptosis, which is the displacement of the eyeball as the infection or abscess pushes the eye in an unnatural direction. Most of these symptoms are easily visible to others and can be quite uncomfortable.

Infections of structures of the inner eye cavity, such as the retina, optic nerve, vitreous fluid, or the blood vessels that feed them, are much more difficult to detect and often cause no pain. Normally, the first symptom of these eye infections is deteriorating vision, which can often be stopped but not reversed. A potential symptom of damage to the inner structures of the eye may be a sudden increase in the number of floaters, which appear as small bubbles, strands, or dark spots or specks that slowly fall across the line of vision.

Screening and Diagnosis

The majority of eye infections are diagnosed by clinical evaluation and observation, although a computed tomography (CT) scan or a magnetic resonance imaging (MRI) scan may be used to confirm or detect infections at the back of the eye or in the surrounding tissues. The mucus, or discharge, from the eye can be collected on a swab and analyzed in a laboratory to determine what organism is causing the infection.

One should have regular eye examinations, during which a doctor will check for the presence of any infections or damage to the inner or outer structures of the eye. General practitioners can often easily diagnose many common eye infections; however, eye care professionals, such as ophthalmologists and optometrists, have specialized equipment that can carefully examine the structures of the eye. They can recognize various eye infections by the appearance of the eye and by the patient’s medical history, because eye infections frequently accompany a disease or infection (such as a cold) in another part of the body.

Treatment and Therapy

Bacterial eye infections (conjunctivitis or keratitis) are often treated with broad-spectrum antibiotic drops, but more specific antibiotics are used for infections caused by chlamydia or gonorrhea. More serious infections, such as cellulitis or endophthalmitis, may require intravenous antibiotics and a hospital stay.

Most cases of viral conjunctivitis will improve within a few days without treatment. Viruses such as herpes simplex remain in the body, and ocular flare-ups may recur; they can be managed with antiviral medications.

The majority of fungal infections can be treated with medication; however, infections such as histoplasmosis, which cause damage to the retina and macula, require surgical laser treatments to slow the deterioration of the macula in an attempt to preserve deteriorating vision.

Eye infections that are manifestations of systemic disease, such as tuberculosis or syphilis, will normally clear up when the entire body is being treated for the systemic infection. Parasitic infection to the eye structures can be destructive and requires aggressive treatment with antimicrobial agents or combinations of topical treatments. Serious cases of keratitis may require surgical debridement. In some cases, the damage to the cornea requires a corneal transplant.

Prevention and Outcomes

To prevent many bacterial or viral eye infections, one should practice good hygiene and safer sex. Washing hands frequently can prevent the spread of organisms that cause infection. Persons with open sores because of shingles, cold sores, or chickenpox, for example, should not touch or treat these sores and then touch their eyes. Children are especially susceptible and should be watched carefully and kept from touching sores, mucus from their nose or mouth, and their eyes. Items such as towels, pillowcases, and cosmetics, that come in contact with eyes, should not be shared. If a family member is known to have an eye infection, it is advised that they use separate washcloths, towels, and bed linens.

Contact lens wearers are particularly susceptible to eye infections and need to wash their hands before they insert or remove their lenses. It is very important that contact lenses are cleaned and cared for as per the manufacturer’s instructions and are not worn longer than advised. Tap water should never come in contact with contact lenses.

Smoking and unprotected exposure to ultraviolet light, such as that from direct sunlight or from tanning beds, can damage the protective layers of the eyes, making them more susceptible to infection.

A person who has had many eye infections could have a sexually transmitted disease, which is highly contagious and is not easily detectable until the infection is visible. Safer sexual practices, such as condom use, will reduce the risk of infection; also, one should always keep hands clean and keep them far from the eyes.

Trauma or scratches make the eye more vulnerable to infection because of damage to the protective layer, making it easier for contaminated foreign bodies to enter the eye. One should take steps to prevent eye injuries by using safety glasses or goggles.

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