Pathological Microbiota on the Corneal Surface and Vicinity of the Eye
Founder Director, Iladevi Cataract and IOL Research Centre, India
Submission: November 18, 2019;Published: November 25, 2019
*Corresponding author: Gupta PD, Founder Director, Iladevi Cataract and IOL Research Centre, Ahmadabad, India JOJ Ophthalmol
How to cite this article:Gupta PD. Pathological Microbiota on the Corneal Surface and Vicinity of the Eye. JOJ Ophthalmol. 2019; 8(1): 555729. DOI: 10.19080/JOJO.2019.08.555729
The eye is in constant touch with environmental microbiota, among them some are pathogenic to human. The pathogenic organisms belong to class bacteria, fungus, virus, protozoans and toxoplasma. They cause various ocular infections due to which our vision suffers. Some infections heal by themselves, whereas others need clinician’s attention. However, to avoid infections strict hygienic conditions are required for the eye.
Keywords:Bacteria; Fungus; Virus; Protozoans; Toxoplasma; Living harmless; Brain, Heart, Lungs, Lysozyme; Haemophilus; Morphological features; Chlamydia
Evolutionary history bacteria show that these organisms can live in extreme hostile environment. Bacteria are minute organisms that are found in almost every ecosystem; from free living harmless to commensal, symbiotic, parasitic and pathogenic to humans. During their adaptation for the various modes of life, their properties also change. They are found even deep seated well protected internal organs such as brain, heart and lungs. Bacteria are the best example to adapt and survive in hostile environment. Because of this, they had to undergo gene mutations very fast, change their morphological features . Eyes are the most important link between external worlds to the brain and therefore, they are well protected from external injuries and bacterial infection. Since the human eye is constantly exposed to the atmospheric components; they are also vulnerable and can easily be damaged due to the ill effects of several bacteria and other pathogens present in the environment. Chronic exposures to toxins produced by bacteria harbor on the surface of the eye and in the vicinity of the eye can damage the eye in various ways. Present review deals with minor and temporary irritation to chronic disorders in the eye due to these parasites. Natural protection given to the eye has been dealt elsewhere [2,3].
Skin microbiota has been studied well and most conjunctival colonization with aerobic bacteria accounts for approximately 50% of healthy people. The inner canthus was the most contaminated site. Coagulase-negative staphylococci are the main components. The normal microbiota prevents colonization by pathogens by competing for attachment sites or for essential nutrients. This is thought to be their most important beneficial effect, which has been demonstrated in the oral cavity, the intestine, the skin, and the vaginal epithelium.
Normal Eye Microbiota
A small number of bacteria are normally present in the conjunctiva. Normally, these organisms are useful for the human host. However, the majority have been too poorly researched to understand the role they play . Those that are expected to be present and do not cause disease (under normal circumstances), but instead participate in maintaining health, are deemed members of the normal microbiota. These include: Chlamydia trachomatis, Chlamydophila pneumoniae, Haemophilus aegyptius, Haemophilus influenzae, Moraxella spp, Neisseria spp, Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus viridians. Staphylococcus epidermidis and certain corny forms such as Propionibacterium acnes are dominant. Sometimes Staphylococcus aureus, Streptococci, Haemophilus sp. and Neisseria sp. are also present. The lachrymal glands continuously secrete tears keeping the conjunctiva moist, while intermittent blinking lubricates the conjunctiva and washes away foreign material. Tears contain bactericides such as lysozyme, so that microorganisms have difficulty in surviving the lysozyme and settling on the epithelial surfaces . Some pathogens able to infect the conjunctiva, such as Neisseria gonorrhoeae and Chlamydia trachomatis are thought to have special processes allowing them to attach to the conjunctival epithelium.
Disease causing microbiota
The inflamed area on eye parts or at the vicinity can be due to either bacterial and/or viral, infections  or allergic reaction due to chemicals. Red eye (hyperaemia), irritation (chemosis) and watering (epiphora) of the eyes are symptoms common to all forms of conjunctivitis. Keratitis, a condition in which the eye’s cornea becomes inflamed, is often marked by moderate to intense pain and usually involves impaired eyesight.
Blepharitis is an inflammation of the eyelids in which they become red, irritated and itchy and dandruff-like scales form on the eyelashes. It is a common eye disorder caused by either bacteria or a skin condition, such as dandruff of the scalp or rosacea. It affects people of all ages.
Common Eye Infections
The outermost layer of the eye and the inner surface of the eyelids are infected most commonly by a virus or, less commonly by a bacterium causes inflammation of the conjunctiva. Neonatal conjunctivitis is often defined separately due to different organisms. An inflamed, red eye (hyperaemia), irritation (chemosis), and watering (epiphora) of the eyes are symptoms common to all forms of conjunctivitis. Bacterial conjunctivitis due to common pyogenic (pus-producing) bacteria causes marked grittiness/irritation and a stringy, opaque, greyish or yellowish muco purulent discharge that may cause the lids to stick together, especially after sleep. Bacteria such as Chlamydia trachomatis or Moraxella can cause a non-exudative but persistent conjunctivitis without much redness . The gritty and/or scratchy feeling is sometimes localized enough for patients to insist they must have a foreign body in the eye. Viral conjunctivitis usually affects only one eye but may spread easily to the other eye. Another symptom that could be caused by bacterial conjunctivitis is severe crusting of the infected eye and the surrounding skin. The more acute pyogenic infections can be painful.
Corynebacterium diphtheriae causes membrane formation in conjunctiva of non-immunized children. Bacterial conjunctivitis usually resolves without treatment. Antibiotics, eye drops, or ointment may only be needed if no improvement is observed after three days [7,8]. Chlamydia conjunctivitis or trachoma was once the most important cause of blindness worldwide . The infection can be spread from eye to eye by fingers, shared towels or cloths, coughing and sneezing, and by eye-seeking flies. Newborns can also develop Chlamydia eye infection through childbirth. Chlamydia can affect infants by causing spontaneous abortion, premature birth, and conjunctivitis, which may lead to blindness and pneumonia. Conjunctivitis due to Chlamydia typically occurs one week after birth
Keratitis is a condition in which the cornea becomes inflamed . Keratitis has multiple causes. Bacterial infection of the cornea can follow from an injury or from result from wearing contact lenses. The bacteria involved are Staphylococcus aureus and, for contact lens wearers, Pseudomonas aeruginosa. Pseudomonas aeruginosa contains enzymes that can digest the cornea. The condition is often marked by moderate to intense pain and usually involves impaired eyesight. Superficial keratitis involves the epithelium of the cornea. After healing, this form of keratitis does not generally leave a scar. Deep keratitis involves deeper layers of the cornea (i.e. the epithelium, Bowman’s membrane and often stroma), and the natural course leaves a scar upon healing that impairs vision if it occurs on or near the visual axis. Infectious keratitis can progress rapidly. In addition to bacteria, fungi and viruses also take part in eye infection. Corneal infection is the most serious and most common vision threatening complication for those wearing contact lenses, which is believed to be strongly associated with contact lens cases
Fungal Infections of the Eye
Factors that contribute to fungal contamination . of contact lenses include, but not limited to, hygiene negligence such as: improper sterilization and disinfection of contact lenses, use of contaminated lenses, contaminated contact lens case, contaminated contact lens solution, wearing of contact lenses during eye infections and introduction of micro-organisms from the environment .
Viral Infections of the Eye
Herpes Simplex Virus Herpes simplex virus (HSV) infection is very common in humans and causes Herpetic simplex keratitis . Cytomegalovirus retinitis is an inflammation of the retina of the eye that can lead to blindness . Caused by human cytomegalovirus, it occurs predominantly in people whose immune system has been compromised.
Parasitic Infections of the Eye
Acanthamoeba is a microscopic, free-living amoeba, commonly found in the environment that can cause rare, but severe, eye illness. Acanthamoeba causes three main types of illness involving the eye . Toxoplasma gondii is a singlecelled parasite causes a disease known as toxoplasmosis. The parasite is found throughout the world ; however, it causes diseases to those who have impaired immune system. Signs and symptoms of ocular toxoplasmosis can include reduced vision, blurred vision , pain (often with bright light), redness of the eye, and sometimes tearing.
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