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What is Keratitis?
Keratitis is the medical term for inflammation of the cornea, the transparent, dome-shaped structure located at the very front of the eye. The cornea acts as a protective window that covers the:
- lens
- pupil
- iris
- and the other internal structures of the eye
Beyond its protective role, the cornea is also responsible for focusing most of the light that enters the eye, which is why any disturbance of its transparency or shape can significantly affect vision. Because the cornea has no blood vessels of its own and relies on the tear film and aqueous humor for nourishment and oxygen, it is particularly vulnerable to injury, infection, and inflammation.
Keratitis can affect people of all ages, from young children to the elderly, and it is generally classified according to the underlying cause. Broadly speaking, keratitis can be triggered by:
-
Infections caused by:
- bacteria
- viruses
- fungi
- protozoa (single-celled parasites)
-
Physical agents, such as:
- ultraviolet (UV) radiation
- mechanical trauma
- penetration of a foreign body into the eye
-
Chemical agents, including irritant or corrosive substances that come into contact with the ocular surface
Certain groups of people are more likely to develop keratitis. Recognized risk factors include:
- individuals who are debilitated or severely weakened by chronic illness
- people with a compromised immune system (for example those undergoing chemotherapy for cancer, those living with HIV/AIDS, or patients on long-term immunosuppressive therapy)
- patients who have recently undergone eye surgery
- people with pre-existing conditions of the eyelids or conjunctiva
- wearers of rigid, non-soft contact lenses, especially when hygiene practices are poor or lenses are worn for extended periods, including overnight
The hallmark symptoms of keratitis typically include:
- excessive tearing (watery eyes)
- eye pain
- red eyes
- fever and a general feeling of being unwell
- sensitivity to light (photophobia)
- blurred vision or other visual disturbances
Diagnosis relies primarily on a thorough medical history and a careful eye examination, most often performed with a slit lamp, a specialized instrument that allows the ophthalmologist to closely inspect the cornea. In select cases, additional laboratory tests, such as corneal scrapings for microbiological culture, may be necessary to identify the responsible pathogen.
Treatment is tailored to the underlying cause but usually involves topical medications (eye drops), such as:
- antibiotics for bacterial infections
- antiviral agents for viral infections
- antifungal medications for fungal infections
- anti-inflammatory drugs, including corticosteroids, used cautiously and only when appropriate
It is important to understand that keratitis is not a condition to be taken lightly. If left untreated, or if the infection is particularly aggressive or resistant to therapy, it can progress to serious complications such as corneal ulceration, scarring, and in the most severe cases, permanent vision loss or blindness. Prompt recognition of symptoms and early treatment by an eye care professional are essential to preserving vision.
Causes
Keratitis can arise from a wide variety of triggers. Understanding the underlying cause is essential because it directly determines the treatment approach. The main categories of causes include:
-
Infectious agents:
- bacteria
- viruses
- fungi
- protozoa
-
Chemical agents:
- toxic substances
- acidic or alkaline compounds
- less commonly, certain medications applied to the eye
-
Physical agents:
- ultraviolet radiation
- mechanical trauma
- presence of a foreign body on or within the eye
Keratitis can also be classified based on the depth of corneal involvement and the presence or absence of an infectious agent:
- Superficial keratitis: involves only the outer layers of the cornea and typically heals without leaving a scar
- Deep keratitis: extends into the deeper corneal layers and can leave permanent scarring or lead to lasting visual impairment
And, based on etiology:
- Infectious keratitis: caused by a pathogen (bacteria, virus, fungus, or protozoan)
- Non-infectious keratitis: caused by trauma, chemical exposure, autoimmune disease, or other non-microbial factors
Superficial Keratitis
In superficial keratitis, the inflammatory process is confined to the outermost layers of the cornea, specifically the epithelium. The main causes of this form include:
-
Actinic (UV-related) causes:
- excessive or unprotected exposure to ultraviolet rays, such as intense sunlight, tanning beds, or snow glare (a condition sometimes called “snow blindness”)
- exposure to welding arcs or other intense artificial light sources without proper eye protection, leading to a condition known as photokeratitis or “welder’s flash”
-
Infectious causes:
- bacterial or viral infections, most commonly caused by Adenovirus, which frequently occur together with conjunctivitis. When both the cornea and conjunctiva are inflamed simultaneously, the condition is more accurately referred to as keratoconjunctivitis
Superficial keratitis is generally considered less severe than deep keratitis because the corneal epithelium has a remarkable capacity for regeneration. In most cases, once the underlying cause is treated, the epithelium heals completely without scarring, and vision is fully restored.
Deep Keratitis
Deep keratitis, more precisely termed interstitial keratitis, involves inflammation extending into the deeper layers of the corneal stroma. Because these deeper layers have a much more limited capacity for regeneration compared to the epithelium, this form of keratitis carries a significantly higher risk of long-term complications, including permanent scarring and vision impairment. In the most severe and poorly controlled cases, interstitial keratitis can progress to blindness.
Historically, the most common cause of interstitial keratitis has been infection with Treponema pallidum, the bacterium responsible for syphilis. Congenital syphilis, in particular, is a classic cause of interstitial keratitis appearing in childhood or adolescence. Other, less common causes of deep keratitis include tuberculosis, herpes virus infections that penetrate beyond the epithelium, and certain autoimmune conditions.
Infectious Keratitis
Infectious keratitis is caused by microorganisms that invade the corneal tissue, triggering an inflammatory response. The pathogens responsible can be grouped into four main categories:
Viruses
- Adenovirus, a common cause of epidemic keratoconjunctivitis, often spread in swimming pools, schools, and healthcare settings.
- Herpes simplex virus, responsible for herpetic keratitis, one of the leading infectious causes of corneal blindness worldwide. This form tends to recur and can cause a characteristic branching ulcer pattern on the cornea known as a dendritic ulcer.
- Herpes Zoster virus (the same virus responsible for chickenpox and shingles), which can cause a severe form of keratitis known as herpes zoster ophthalmicus when the virus reactivates in the branch of the trigeminal nerve that supplies the eye.
Bacteria
- Treponema pallidum, the causative agent of syphilis.
- Mycobacterium tuberculosis, responsible for tuberculosis.
- Staphylococcus aureus, one of the most frequent causes of bacterial keratitis, particularly in contact lens wearers.
- Pseudomonas aeruginosa, a particularly aggressive bacterium strongly associated with contact lens-related keratitis, capable of causing rapid corneal destruction if not treated promptly.
- Chlamydia trachomatis, which causes trachoma (a leading infectious cause of blindness in developing countries), lymphogranuloma venereum, and pelvic inflammatory disease in women.
Protozoa
- Acanthamoeba, a free-living amoeba commonly found in fresh water, soil, and tap water, especially when contaminated. Acanthamoeba keratitis is strongly associated with contact lens use, particularly when lenses are rinsed with tap water or worn while swimming. This infection is notoriously difficult to treat and can cause severe pain and prolonged corneal damage.
Fungi
- Candida albicans, which more commonly affects immunocompromised individuals or those with pre-existing corneal damage;
- Aspergillus species, often associated with agricultural trauma involving plant material;
- Fusarium species, historically linked to outbreaks associated with certain contact lens solutions.
Fungal keratitis, while less common than bacterial or viral forms, tends to be more insidious in onset and more difficult to diagnose and treat, often requiring prolonged courses of antifungal therapy.
Non-Infectious Keratitis
Not all cases of keratitis are caused by an infectious organism. Non-infectious keratitis can result from:
- prolonged or intense exposure to ultraviolet rays, causing actinic (UV) keratitis, also known as photokeratitis.
- penetration of a foreign body into the eye, such as a splinter of wood, metal, or glass.
- trauma, for example resulting from car accidents, sports injuries, or physical altercations.
- complications of eye surgery, including cataract surgery, corneal transplantation, or refractive surgery (such as LASIK).
- autoimmune diseases, including:
- Sjögren’s syndrome, which is strongly associated with dry eye syndrome and can predispose to keratitis due to insufficient tear production and lubrication.
- rheumatoid arthritis, which can cause peripheral ulcerative keratitis, a serious complication involving thinning and ulceration at the edge of the cornea.
- various forms of vasculitis, which can compromise blood flow to ocular tissues and trigger inflammatory damage to the cornea.
In these non-infectious cases, management focuses on controlling the underlying systemic condition, protecting the ocular surface, and preventing secondary infection.
Risk Factors
While anyone can develop keratitis, certain factors substantially increase the likelihood of its occurrence. Being aware of these risk factors can help patients take preventive measures and seek prompt care when symptoms appear.
-
Contact lens use: This is among the single most important risk factors for infectious keratitis, particularly bacterial and Acanthamoeba keratitis. Risk increases with:
- extended or overnight wear.
- poor lens hygiene (not washing hands before handling lenses, using tap water to rinse lenses or lens cases, not replacing lens cases regularly).
- wearing lenses while swimming or showering.
- using expired contact lens solutions.
-
Ocular trauma: Any injury that breaches the corneal surface, even a minor scratch, can serve as an entry point for microorganisms.
-
Dry eye disease: Insufficient tear production compromises the natural protective barrier of the ocular surface, making it more susceptible to irritation and infection.
-
Immunosuppression: Conditions such as HIV/AIDS, diabetes, cancer chemotherapy, or long-term corticosteroid use weaken the body’s ability to fight off infections, including those affecting the eye.
-
Previous ocular surgery: Surgical procedures, particularly corneal transplants and refractive surgeries, can alter the corneal surface and increase vulnerability to infection.
-
Eyelid or conjunctival disorders: Conditions that prevent proper eyelid closure or that alter the normal tear film distribution (such as entropion, ectropion, or blepharitis) can predispose to keratitis.
-
Environmental and occupational exposure: Outdoor workers, welders, and individuals frequently exposed to intense sunlight or artificial UV sources without adequate eye protection are at higher risk for actinic keratitis.
-
Living in or traveling to areas with poor water sanitation: This increases the risk of exposure to waterborne pathogens such as Acanthamoeba.
Symptoms
The symptoms of keratitis can vary depending on the underlying cause, the depth of corneal involvement, and the severity of the inflammation. However, certain symptoms are common across most forms of the condition:
- Epiphora, or excessive tearing.
- Photophobia, an abnormal sensitivity or discomfort in response to normal light exposure.
- Headache, which can accompany the eye pain, particularly in more severe or infectious forms;
- a persistent sensation of a foreign body in the eye, even when none is present.
- eye pain, ranging from mild irritation to severe, debilitating discomfort.
- redness of the eye, due to dilation of the blood vessels surrounding the cornea.
- fever, fatigue, and a general feeling of malaise, particularly in infectious cases with a systemic component;
- difficulty opening the eyes, often due to pain and light sensitivity.
- blepharospasm, an involuntary and persistent closing of the eyelids, which the body uses as a protective reflex;
- blurred vision and difficulty focusing, which may worsen as the inflammation progresses.
It is worth noting that the intensity of symptoms does not always correlate directly with the severity of the underlying damage. Some serious infections, particularly certain fungal or Acanthamoeba infections, can present with symptoms disproportionately mild compared to the extent of corneal damage, which is one of the reasons delayed diagnosis remains a significant clinical challenge.
In severe cases, especially in patients who are debilitated, immunocompromised, or who delay seeking treatment, keratitis can progress toward serious complications, discussed in detail below.
Possible Complications
Keratitis should never be underestimated, as it carries the potential for serious, sight-threatening complications if not promptly and appropriately managed. The most significant complications include:
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Corneal ulcer: A localized area of tissue loss and infection on the cornea, which can be extremely painful and, if deep, can perforate the eye.
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Corneal scarring (leukoma): Once inflammation extends beyond the epithelium into the stroma, the healing process may result in permanent scar tissue, which can obstruct vision if located in the central visual axis.
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Glaucoma: Inflammation and the use of certain medications (particularly prolonged corticosteroid use) can raise intraocular pressure above normal levels, potentially damaging the optic nerve.
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Corneal perforation: In the most severe, untreated, or rapidly progressive cases (particularly bacterial or fungal infections), the cornea can perforate, representing a true ophthalmologic emergency.
-
Endophthalmitis: A severe infection that spreads to the internal structures of the eye, posing a significant risk to the eye’s structural integrity and function.
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Permanent vision loss or blindness: In the most severe cases, particularly when treatment is delayed, inappropriate, or when the causative organism is highly aggressive (as with certain strains of Pseudomonas or Acanthamoeba), the end result can be irreversible vision loss.
Given these risks, it is essential to seek prompt medical evaluation at the first sign of eye redness, pain, or visual disturbance, particularly in contact lens wearers, individuals with a compromised immune system, or those who have recently experienced ocular trauma.
Diagnosis
An accurate and timely diagnosis is the cornerstone of successful keratitis management, as it allows the treating physician to identify the underlying cause and initiate the most appropriate therapy without delay.
Medical history (anamnesis)
The diagnostic process begins with a detailed medical history. During this conversation, the physician asks a series of targeted questions to reconstruct both the patient’s current symptoms and their broader medical background. Key information gathered typically includes:
- onset and duration of symptoms.
- history of contact lens use and hygiene practices.
- recent ocular trauma or surgery.
- exposure to potentially contaminated water sources.
- history of cold sores, shingles, or other herpes virus infections.
- underlying systemic or autoimmune conditions.
- immune status and any immunosuppressive medications or conditions.
Clinical examination
The physical examination allows the physician to correlate the patient’s reported symptoms with objective clinical findings. The ophthalmologist will assess:
- visual acuity.
- the pattern and degree of redness.
- pupil reactivity.
- the presence of discharge.
- eyelid function.
Slit-lamp examination
The single most valuable diagnostic tool for keratitis is the slit lamp, a specialized microscope equipped with an adjustable, high-intensity light source. This instrument allows the ophthalmologist to examine the cornea and other anterior eye structures in remarkable detail, revealing characteristic patterns of damage, such as:
- dendritic (branching) ulcers, typical of herpes simplex keratitis.
- diffuse haze or infiltrate, more typical of bacterial or fungal infections.
- ring-shaped infiltrates, which can be suggestive of Acanthamoeba keratitis.
- depth and extent of stromal involvement.
The physician may also use special dyes, such as fluorescein, which highlight areas of epithelial damage under blue light, making even small corneal defects clearly visible.
Microbiological testing
When an infectious cause is suspected, particularly in moderate to severe cases or those not responding to initial empirical treatment, the ophthalmologist may collect a corneal scraping for laboratory analysis. This sample can be sent for:
- Gram staining and bacterial culture.
- fungal culture and staining.
- PCR (polymerase chain reaction) testing for viral DNA, particularly herpes simplex and varicella-zoster virus.
- specific staining and culture techniques for Acanthamoeba.
Identifying the exact causative organism is particularly important in cases that fail to respond to initial broad-spectrum treatment, as it allows the physician to tailor therapy precisely, using the most effective antimicrobial agent for the specific pathogen involved.
Treatment
The treatment approach for keratitis is fundamentally guided by its underlying cause. Prompt and appropriate treatment is essential not only for symptom relief but, more importantly, to prevent the serious complications described above.
Bacterial keratitis
Treatment typically involves:
- topical antibiotic eye drops, often started empirically (broad-spectrum) while awaiting culture results, then adjusted based on the specific organism identified and its sensitivity profile.
- in more severe cases, fortified (concentrated) antibiotic preparations may be required, sometimes administered very frequently, even hourly, during the initial phase of treatment.
- corticosteroids, used topically or systemically in select cases, to help control the inflammatory response once the infection is adequately controlled with antibiotics. Corticosteroids must be used cautiously and only under close ophthalmologic supervision, since inappropriate use can worsen certain infections.
Viral keratitis
When the causative agent is a virus, such as Adenovirus or Herpes simplex/zoster:
- specific antiviral medications are used, either topically (as eye drops or ointments) or, in more severe or recurrent cases, orally.
- corticosteroids are generally avoided or used with extreme caution in active herpetic epithelial disease, as they can worsen viral replication and lead to more extensive corneal damage. However, in certain stromal forms of herpetic keratitis, low-dose corticosteroids may be carefully introduced under specialist supervision alongside antiviral coverage.
Fungal keratitis
Fungal infections of the cornea require prolonged treatment with topical antifungal medications, and in some cases systemic antifungal therapy is also necessary. Treatment courses tend to be longer than for bacterial infections, often extending over several weeks, given the slower response of fungal organisms to therapy.
Acanthamoeba keratitis
This form of keratitis is notoriously challenging to treat and typically requires a combination of specific anti-amoebic topical medications, administered intensively over an extended period, sometimes lasting several months.
Non-infectious keratitis
When keratitis results from a non-infectious cause, such as trauma, chemical exposure, or an underlying autoimmune condition, treatment focuses on:
- addressing the underlying cause directly, for example surgically removing a foreign body from the eye.
- using topical antibiotics as a preventive measure against secondary bacterial infection, since a damaged corneal surface is more vulnerable to opportunistic invaders.
- using corticosteroid eye drops to reduce inflammation, when appropriate.
- managing any underlying systemic autoimmune disease with the appropriate systemic therapy, in collaboration with a rheumatologist or immunologist when needed.
Supportive and adjunctive treatments
In many cases, regardless of the underlying cause, additional supportive measures can help promote healing and improve patient comfort:
- artificial tears to lubricate and rehydrate the ocular surface, particularly useful in cases associated with dry eye or reduced tear production.
- bandage contact lenses, which can be used in select cases to protect the healing corneal surface.
- cycloplegic eye drops, which temporarily paralyze the eye’s focusing muscles, helping to reduce pain associated with muscle spasm and light sensitivity.
Surgical treatment
In the most severe, selected cases, where medical therapy alone is insufficient to control the infection or where significant scarring has already compromised vision, surgical intervention may be necessary. This can include:
- corneal transplantation (keratoplasty), using tissue from a donor to replace the damaged or scarred cornea, restoring corneal clarity and, in many cases, meaningfully improving vision.
Prevention
Given the potentially serious consequences of keratitis, prevention plays a crucial role, particularly for individuals who fall into higher-risk categories, such as contact lens wearers. Recommended preventive measures include:
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Careful contact lens hygiene: always wash and dry hands thoroughly before handling lenses, use only recommended lens care solutions (never tap water), and replace lens storage cases regularly.
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Avoid prolonged contact lens wear: extended or overnight use of contact lenses significantly increases infection risk. Daily disposable lenses, changed every day, are generally considered the safest option for reducing the risk of infectious keratitis.
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Never wear contact lenses while swimming or showering, as this significantly increases exposure to waterborne pathogens such as Acanthamoeba.
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Wear protective eyewear: sunglasses with adequate UV protection should be worn during prolonged sun exposure, and appropriate protective goggles or shields should always be used by welders and other workers exposed to intense artificial light sources or potential eye trauma.
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Prompt treatment of eyelid and ocular surface conditions: conditions such as blepharitis or dry eye should be properly managed, as they can predispose to keratitis if left untreated.
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Routine eye examinations: particularly important for individuals with autoimmune conditions or those who have undergone eye surgery, to catch early signs of corneal inflammation before complications develop.
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Avoid touching or rubbing the eyes with unwashed hands, particularly during outbreaks of viral conjunctivitis, to reduce the risk of viral keratoconjunctivitis.
Frequently Asked Questions
Is keratitis contagious?
It depends on the underlying cause. Viral keratitis, particularly that caused by Adenovirus, can be highly contagious and spreads easily through contact with contaminated hands, surfaces, or ocular secretions. Bacterial, fungal, and Acanthamoeba keratitis are generally not considered contagious in the traditional sense, though the underlying risk factors, such as poor contact lens hygiene, may be shared among people in close contact.
Can keratitis heal on its own without treatment?**
Some very mild, superficial forms of keratitis, particularly those related to minor UV exposure, may improve on their own with rest and lubrication. However, most cases of keratitis, particularly infectious forms, require prompt medical treatment to prevent progression and serious complications. Self-treatment or delaying medical evaluation can significantly increase the risk of permanent vision damage.
How long does it take for keratitis to heal?**
Recovery time varies significantly based on the cause and severity. Mild superficial keratitis may resolve within a few days to a week with appropriate treatment. More severe infectious forms, particularly fungal or Acanthamoeba keratitis, can require several weeks to months of treatment to fully resolve.
Can keratitis cause permanent blindness?**
Yes, in severe or inadequately treated cases, keratitis can lead to significant corneal scarring, perforation, or secondary complications such as glaucoma, all of which can result in permanent vision loss. This is why early diagnosis and appropriate treatment are so critical.
Should I stop wearing contact lenses if I develop keratitis?**
Yes. If keratitis is suspected or diagnosed, contact lens wear should be discontinued immediately until the condition has fully resolved and an eye care professional confirms it is safe to resume use.
Sources and Bibliography
- Kanski – Clinical Ophthalmology. Brad Bowling, C. Azzolini, S. Donati (eds.). EDRA Publishing.
- Medscape: Bacterial Keratitis
- Medscape: Ultraviolet Keratitis
- Stapleton F, Keay L, Edwards K, et al. The incidence of contact lens-related microbial keratitis in Australia. Ophthalmology. 2008;115(10):1655–1662.
- Liesegang TJ. Herpes simplex virus epidemiology and ocular importance. Cornea. 2001;20(1):1–13.
- Dart JK, Radford CF, Minassian D, Verma S, Stapleton F. Risk factors for microbial keratitis with contemporary contact lenses: a case-control study. Ophthalmology. 2008;115(10):1647–1654.
- Wilhelmus KR, Gee L, Hauck WW, et al.; Herpetic Eye Disease Study Group. Herpetic Eye Disease Study: a controlled trial of topical corticosteroids for herpes simplex stromal keratitis. Ophthalmology. 1994;101(12):1883–1895.
- Srinivasan M, Mascarenhas J, Rajaraman R, et al. Corticosteroids for bacterial keratitis: the Steroids for Corneal Ulcers Trial (SCUT). Archives of Ophthalmology. 2012;130(2):143–150.
- Dart JKG, Said DG, Resnikoff S, et al. Acanthamoeba keratitis. Nature Reviews Disease Primers. 2017;3:17072.
- Thomas PA, Kaliamurthy J. Mycotic keratitis: epidemiology, diagnosis and management. Clinical Microbiology and Infection. 2013;19(3):210–220.
