Keratitis is an inflammation or irritation of the cornea; the clear, round dome covering the iris and pupil of the eye, and it is mostly associated with extended-wear contact lenses.

The most common cause of infectious keratitis is bacteria, but it may also be caused by fungi, viruses, mycobacteria and protozoa Noninfectious keratitis can be caused by a minor injury, wearing the contact lenses too long or other noninfectious diseases.

Risk factors that can lead to keratitis include prolonged use of contact lenses, reduced immunity, eye injury, changes in the corneal surface, and corneal edema.

The pathophysiological mechanism of keratitis usually begins by invading the stroma of the cornea by pathogens, that begin to release enzymes that help in digestion and degradation of the corneal matrix such as proteases, lipases, fibrinolysins enzymes, collagenases, coagulases.

Signs and symptoms associated with keratitis may include difficulty opening the eyelid, pain or irritation, sensitivity to light and blurred vision.

To diagnose keratitis, the healthcare provider may begin by taking the medical history and then he/she may perform a complete physical examination to evaluate vision, pupil assessment, and intraocular pressure. He/she may use specific methods such as penlight exam and slit-lamp exam as well as analyzing a sample of tears or some cells from the cornea by sending it to the laboratory.

Treatment options of keratitis differ according to causes of keratitis. Topical antibiotic treatment and /or cycloplegics may be suggested in cases of bacterial keratitis. Keratitis caused by fungi typically requires antifungal eyedrops and oral antifungal medication. Oral antiviral medications may be prescribed for viral keratitis. However, Acanthamoeba keratitis is hard to treat and may require a combination of an antibiotic, antiviral, antifungal, and antiparasitic drugs

If not managed well, keratitis can lead to various complications such as bullous keratopathy which is permanent swelling of the cornea irregular astigmatism; a non-uniform corneal steepening, endophthalmitis, pus-containing inflammation of the intraocular fluids.

 corneal perforation, and blindness. Many specialists recommend several preventive measures for keratitis such as appropriate contact lenses care that involves proper hand washing before handling contact lenses and replacing the contact lens case every three to six months.

Other specialists suggest using contact lenses less often because wearing contact lenses can increase the risk of viral keratitis recurrences. It is worth mentioning that most types of keratitis are curable with early treatment, but poor prognosis is reported frequently among patients with mixed bacterial and fungal keratitis

Keratitis is an inflammation or swelling of the cornea, which is the clear, round dome covering the iris and pupil of the eye . Bacteria, viruses, fungi or parasites and in other cases the insertion of a foreign body into the cornea are the reasons behind keratitis. The outcomes of keratitis are visual clarity reduction, corneal discharges, a painful red eye and corneal erosion; when the outermost layer named the epithelium is improperly attached to the corneal tissue below. Keratitis is more common among people who use extended-wear contact lenses. It could lead to blindness within a few days, if not treated quickly.

Keratitis can be classified into many types depending on the cause including:

• Noninfectious keratitis

 Non-infectious keratitis can be attributed to a simple fingernail scratch or wearing the contact lenses for too long, causing an inflammatory reaction in the cornea.

• Infectious keratitis

 This type involves infections that relate to different pathogens such as:

• Bacterial keratitis

 Bacterial keratitis is known as 'corneal ulcer'. The incidence of keratitis is higher in people who wear contact lens and to a lesser extent in people who do not. Severe cases of this type could lead to vision loss.

• Fungal keratitis

 This type of keratitis is caused by many types of fungi and is considered as a critical ocular infection with potentially harmful visual results.

• Acanthamoeba Keratitis

It is also called parasitic, amebic, protozoal keratitis, is a rare, serious vision-threatening infection seen mostly among contact lens wearers.

• Viral keratitis

 Herpes simplex virus (HSV) and the varicella-zoster virus (VZV)  are the common causes of this infection, with the (HSV) being the more prevalent.All layers of the cornea and the surrounding structures are either directly invaded or get infected as a result of secondary inflammations. Unless very severe, the infection usually heals without causing serious damage to the eye, where blindness or scarring of the cornea accompanies the more serious forms of the infection.

• Other infectious keratitis include:

1. Luetic interstitial keratitis

 This type of keratitis is usually associated with syphilis infection and may result in stromal inflammation.

1. Microsporidial keratitis

 This type of keratitis is mostly seen in patients with weakened immunity

1. Infectious crystalline keratopathy

 This type of keratitis is a chronic, rare, slowly progressing infection that is related to (HSV), acanthamoebic keratitis, and long-term topical steroid therapy.

Causes of infectious and noninfectious keratitis are:

• Infectious keratitis

 With bacteria being the most common cause of infectious keratitis, fungi, viruses, mycobacteria, and protozoa may also cause infectious keratitis.

• The most common bacterial corneal pathogens are:

1. Pseudomonas species, Gram-negative bacteria, found in soil and water.
2. Staphylococcus species, Gram-positive bacteria,  that normally live on human skin and on the mucous membrane.
3. Streptococcus species; Gram-negative bacteria
4. Other Gram-negative organisms.

• The most common fungal corneal pathogens are :

1. Fusarium species.
2. Aspergillus species.

• Candida species. The most common viral corneal pathogens are :

1.  (HSV) which is divided into 2 types, herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2).
2.  (VZV) which is a virus that belongs to the α-herpesvirus family and is specific to humans.

•  Acanthamoeba keratitis is caused by Acanthamoeba species that infects the cornea.

• Noninfectious keratitis

 Noninfectious keratitis can be caused by a minor injury, a prolonged use of the contact lenses or other noninfectious diseases.The more common entities of noninfectious keratitis are:

• Peripheral ulcerative keratitis (PUK) caused by an auto-immune disease.
• Phlyctenular keratitis due to a hypersensitivity reaction to a foreign antigen.
• Vernal ulcer or shield ulcer; an atopic condition of the external ocular surface.
• Staphylococcal marginal keratitis; inflammation of the outer edge of the cornea.
• Contact lens-related sterile infiltrates.
• Meta herpetic ulcer; a condition that results from the inability of the epithelium to heal.

There are many risk factors that may increase the risk of keratitis include:

• Contact lenses

 The risk of both infectious and noninfectious keratitis increases among people who wear contact lenses,  especially if worn continuously or for prolonged periods of time or in the case of inadequate lens disinfection such as contaminated or home-prepared ocular solutions.

• Reduced immunity

Immunocompromised systems that result from disease or medications, such as altered ocular defense mechanisms due to topical or systemic immune suppression, can increase the risk of developing keratitis.

• Eye trauma

 The chance of developing keratitis increases with a previous injury to the cornea. Loose sutures with adjacent infections such as blepharitis; a condition that involves the inflammation of the eyelid margins, and viral keratitis.

• Changes in the corneal surface

•  These changes  

 could be attributed to dry eye, eyelid misdirection, and exposure.

• Corneal epithelial abnormalities

 Such abnormalities may result from several disorders such as neurotrophic keratopathy; a degenerative disease that is manifested in decreased corneal sensitivity and poor corneal healing.

• Corticosteroids

Corticosteroid eyedrops used in treating an eye disorder can either increase the risk of developing infectious keratitis or worsen existing keratitis.

• Systemic disease

 Certain diseases can increase the risk of developing keratitis such as diabetes, debilitating disease, and hypovitaminosis A.

• Poor nutrition

 The lack of the appropriate nutrients can raise the possibility of developing keratitis, especially vitamin A.

• Warm climate

A warm, humid climate favors the risk of developing keratitis. Moreover, plant material in such a climate can scratch the corneal epithelium, whereas the chemicals found in these plants can cause an inflammation followed by an infection.

Bacterial pathogens remain the most aggressive and destructive kind of pathogens invading the cornea.The corneal stroma is targeted by bacteria but only after it has penetrated seven layers of corneal epithelial cells located on top of the stroma. Injuries or diseases that subject the stroma to exposure to the surface, gives the bacteria a direct access to the stroma without the need to pass these layers.

The corneal matrix is digested and degraded by several bacterial toxins and enzymes. These toxins and enzymes are either exotoxins; produced by active bacteria or endotoxins; produced after the death of the bacteria, including proteases, lipases, fibrinolysins enzymes, collagenases, coagulases, enzymes produced by polymorph nuclear cells. Immediate recognition and initiation of treatment is critical in order to prevent visual loss since the process of corneal destruction can rapidly occur, usually within 24 hours with virulent organisms.

The changes that occur during bacterial corneal infections include the activation of the fibrinolytic system by converting plasminoge; a glycoprotein made in the liver, to plasmin, which lyses fibrin clots to fibrin degradation products. Epithelial microlesions can result from protease, chymase and tryptase, in addition  thedegradation of adhesive glycoproteins by proteolytic enzymes can delay the healing process.

These may include:

• Activity in the anterior chamber of the eye (flare, cells, pus or coagulum if severe).
• Difficulty opening the eyelid due to pain or irritation.
• Corneal lesion, usually single (central or mid-peripheral).
• Excess tears or other discharge from the eye.
• Burning, itchy or gritty feeling in the eye.
• Conjunctival hyperemia and infiltration.
• A feeling that something is in the eye.
• Photophobia; sensitivity to light.
• Epiphora (watering eyes).
• Swelling around the eye.
• Decreased vision.
• Blurred vision.
• Eye redness.
• Lid edema.

Diagnosis of keratitis can involve the following steps:

• Medical history

A fully detailed history of the patient is necessary that includes a past medical history such as medications and eye drops, allergies, family history and past ocular history that documents the occurrence of trauma, previous eye diseases or surgeries. Furthermore, a healthcare provider may ask about the characteristics and onset of symptoms, in addition to doing activities like swimming while wearing contact lenses and specific details related to wearing, cleaning, quality contact lenses.

• Complete eye examination

The exam includes a test to determine visual acuity or the quality of vision, usually by using standard eye charts. Methods can be used to perform comprehensive eye examination include:

• Penlight exam

A penlight is used to examine the pupil's reaction, size, and other factors. The surface of the eye could be stained in order to help identify ulcers of the cornea and other surface irregularities.

• Slit-lamp exam

This method is also called biomicroscopy. It lights up the cornea, lens, iris, and the space between the iris and cornea using an intense line of light, which provides a clear view and magnification, enabling the doctor to determine the level and characteristics of keratitis, in addition to the extent of its effect on the rest of the structures of the eye.

• Laboratory analysis

The analysis of a sample of tears in this test is able to determine the cause of keratitis and provide a treatment plan for the condition of the patient. Gram and Giemsa staining of the corneal smears determine the existence of the microorganisms, their sensitivity to antibiotics, in addition to differentiating bacterial ulcers from fungal ulcers.

Variable causes lie behind keratitis; therefore, treatment is based on diagnosis. Treatment for keratitis is as follows:

• For noninfectious keratitis

The cause of this type is the guide for treatment. Treatment may not be required if keratitis results from a scratch or due to extended contact lens wear. In some cases for a patient to improve, the need to apply prescription medication to the eye and wear an eye patch if there is significant tearing and pain, is necessary.

• For infectious keratitis

  The cause of the infection determines the type of treatment, which are:

• Bacterial keratitis

Mild cases require antibacterial drops, whereas moderate to severe cases oral antibiotics should be used. To treat this form of keratitis, patients may need intensive topical antibiotic treatment and /or cycloplegics. Antibiotics such as fluoroquinolone drops may be given every 2 to 6 hours and topical steroids may be administered carefully during the healing stage. Cyanoacrylate tissue glue adhesive can be suggested to treat small corneal perforations and descemetoceles, which is a herniation in an intact descemet membrane as a result of trauma, inflammation or infection.

• Fungal keratitis

 Managing this type requires topical and or systemic anti-fungal therapy either separately or in combination with surgery. The main treatment is antifungal eyedrops and oral antifungal medication. Natamycin is the most commonly used antifungal.  Severe forms require systemic antifungal treatment. When these treatments are not successful, conjunctival flaps, lamellar or penetrating keratoplasty are used with keratoplasty being essential in fungal keratitis management.

• Viral keratitis

 This involves eye drops and oral antiviral medications that do not completely dispose of the virus, leading to recurrent viral keratitis.

• Acanthamoeba keratitis

 This form of keratitis can be difficult to treat, but usually, topical amebicides are used in association with topical steroids and in severe cases, therapeutic penetrating keratoplasty. Successful treatment was proved using variouscombinations of antibiotic, antiviral, antifungal, and antiparasitic drugs.

Potential complications of keratitis include:

• Bullous keratopathy where the cornea becomes permanently swollen and secondary lipid keratopathy which is the deposition of material and thinning of tissue associated with previous ocular injury or pathology.
• Irregular astigmatism; a non-uniform corneal steepening.
• Endophthalmitis; a pus containing inflammation of the intraocular fluids.
• Epitheliopathy; a disease of the epithelium.
• Chronic or recurrent viral infections of the cornea.
• Temporary or permanent reduction in the vision.
• Glaucoma where the optic nerve is damaged.
• Corneal ulcers, which are open sores on the cornea.
• Neurotrophic and metaherptic ulcers.
• Scleral extension of the infection.
• Anterior segment disruption.
• Chronic corneal inflammation.
• Residual corneal scarring.
• Corneal perforation.
• Blindness.

Preventive measures to prevent keratitis may include:

• Appropriate contact lenses care

 These include:

• The daily using of contact lenses is allowed, but it is advisable to remove them out during the night.
• Proper hand washing with liquid soap and water before handling contact lenses, especially if the person has a cold sore or herpes blister.
• Replacing and cleaning the contact lenses according to the instructions of the eye care specialist, in addition to seeking his/her consultancy prior using eye drops.
• Using compatible, sterile products and accessories, with the type of lenses.
• Avoid scratching the lenses by avoiding any rough movements.
• Removing contact lens when it causes discomfort or when redness appear.
• Replacing the case of contact lenses every three to six months.
• Replacing the solution in the contact lens case each time the lenses are cleaned.
• Activities involving contact with water such as showering and swimming requires removing the contact lens.
• Wearing protective eyewear is advisable for workers in agriculture and generally for people who are at risk for eye trauma.

• Preventing viral contamination

 Some of the measures that help prevent the recurrence of viral keratitis include:

• Practice hand wishing before touching the eyes or the eyelids in case the person have a cold sore or herpes blister.
• Corticosteroid eyedrops should only be used upon prescription way because it can raise the risk of developing a viral form of keratitis.
• Decrease or stop the use of contact lenses when wearing contact lenses increases the risk of viral keratitis recurrences.

• Other preventive measures:

• Never expose the contact lenses to wetness with tap water, bottled water, or with body secretions such as saliva.
• Getting sufficient amounts of vitamin A by eating a well-balanced diet or by taking multiple-vitamin supplements containing vitamin A.

The size, location, depth, cause of keratitis, and any pre-existing ocular conditions are vital for the prognosis of bacterial keratitis. When keratitis is treated at an early stage, most types of keratitis are curable.

Prevention is critical in Acanthamoeba keratitis  cases since this type has been identified with the worst prognosis. However, early detection of Acanthamoeba keratitis yields to satisfactory outcomes. Viral keratitis has good prognosis, although the severity and number of recurrences of the disease determine its extremely variable prognosis .Poor prognosis is common among patients with mixed bacterial and fungal keratitis.

• According to a study published in Sultan Qaboos University Medical Journal, bacterial keratitis is one of the recognizable causes of corneal opacifications, which is the second common cause of blindness worldwide after cataracts.
• According to a study carried out by the National Center for Emerging and Zoonotic Infectious Diseases, which is part of Centers for Disease Control and Prevention (CDC) in the USA, nearly 1 million clinical visits for keratitis occur every year, where contact lenses wear is considered the largest singlerisk factor for microbial keratitis.
• According to a study published in the Middle East African Journal of Ophthalmology, the major risk factor for microbial keratitis in Bahrain was contact lens wear. Pseudomonas aeruginosa was the predominant bacteria isolated. The major risk factor among contact lens wearers was sleeping with the contact lenses.
• According to results of a doctoral thesis presented  at the University of New South Wales, which describes the incidence rates  and risk factors for contact lens related microbial keratitis in Australia and New Zealand, risk factors for infection were overnight use of lenses, poor lens case hygiene, high socio-economic status, less than 6 months experience in current lens type ,and smoking.