Introduction

Keratoconjunctivitis is an inflammatory condition which affects the two outer layers of the eye, the cornea and conjunctiva. Keratitis is the inflammation of the cornea, while conjunctivitis is the inflammation of the conjunctiva. In keratoconjunctivitis, both keratitis and conjunctivitis occur simultaneously.^1,2

This condition can be triggered by various factors, broadly categorised as infectious, such as viral or bacterial agents, and non-infectious causes, including allergies, autoimmune conditions, and environmental irritants.^1,2

Symptoms typically include:^1,2

• Redness
• Sensitivity to light
• Blurred vision 
• Dryness of the eye
• Excessive tearing
• Sensation of a foreign body in the eye

Treatment is highly dependent on the suspected trigger; therefore, a thorough investigation and examination of the causes of keratoconjunctivitis are essential to receive the correct management and prevention of more severe complications.

Causes of keratoconjunctivitis

Causes of keratoconjunctivitis are generally divided into those resulting from infectious or non-infectious triggers. Infectious forms most commonly result from viral or bacterial agents, though fungal and parasitic infections may also occur. Non-infectious keratoconjunctivitis can arise from allergic reactions, exposure to toxic substances, foreign bodies, or autoimmune-mediated inflammation.^1,2

Infectious causes of keratoconjunctivitis

Viral

Viral infections are the most common infectious cause of keratoconjunctivitis. The viruses most frequently associated with the condition include:^3-5

• Adenovirus – this virus accounts for up to 75% of viral keratoconjunctivitis cases and represents the most common infectious cause overall. It is highly contagious and is responsible for epidemic outbreaks
• Herpes simplex virus (HSV) – this virus causes a more severe form of keratoconjunctivitis, often due to recurrent HSV infections involving the cornea. It can lead to severe complications such as recurrent keratitis and dendritic ulcerations
• Varicella-zoster virus (VZV) – this virus may cause keratoconjunctivitis in association with herpes zoster ophthalmicus, particularly in older adults or immunocompromised individuals
• Cytomegalovirus (CMV) – this virus typically occurs in immunocompromised individuals, such as those with HIV/AIDS or organ transplant recipients

Bacterial

The most common cause of bacterial keratoconjunctivitis is contact lens use. The bacteria most frequently associated with the condition include:⁶

• Staphylococcus aureus, Streptococcus pneumoniae – these bacteria are the most common causes of a sudden onset of  bacterial keratoconjunctivitis
• Pseudomonas aeruginosa – this bacterium causes a more severe bacterial infection. It is more common in individuals who wear contact lenses and can lead to a hole in the cornea if left untreated
• Neisseria gonorrhoeae, Chlamydia trachomatis – these bacteria are often the cause of keratoconjunctivitis in newborns, typically presenting within the first few days of life

Fungal

Fungal causes are rare. The most common fungal species to cause keratoconjunctivitis are the Candida, Aspergillus and Fusarium species. Fungal causes need to be treated very rapidly, as they can cause long-term complications which can impact vision. These usually occur as a result of:⁷

• Opportunistic infections in immunocompromised individuals
• Trauma-related cases often occur in individuals involved in agricultural work, particularly those exposed to vegetative matter, or in contact lens wearers. Such trauma can predispose the cornea to secondary infection and inflammation

Parasitic

Parasitic keratoconjunctivitis is most commonly caused by Acanthamoeba or Pythium species. These infections are typically associated with poor contact lens hygiene or exposure to contaminated water. They can be sight-threatening if diagnosis and treatment are delayed.⁸

Non-infectious causes of keratoconjunctivitis

Allergic

Here, keratoconjunctivitis arises as a result of various factors, including genetics, or environmental allergens like pollen, pollution and pets. Allergic conjunctivitis is subdivided into:^9,10

• Seasonal allergic conjunctivitis (SAC) – these occur during specific months of the year due to exposure to simple allergens
• Vernal keratoconjunctivitis (VKC) – this is a severe allergic form, affecting children and young adults typically living in warm areas, due to both allergen and climate exposure
• Atopic keratoconjunctivitis (AKC) – this is a form of allergic keratoconjunctivitis which lasts a long duration of time, usually as a result of various factors such as allergens and genetics. If left untreated, it can lead to scarring in the cornea of the eye and ultimate vision impairment

Autoimmune and systemic conditions

Many autoimmune conditions are associated with keratoconjunctivitis, including:^11,12

• Sjögren’s syndrome – this is an autoimmune disease, where people may have a reduced production of tears, resulting in a severely dry eye, which can cause inflammation
• Rheumatoid arthritis – this is an autoimmune condition where the immune system attacks the tear (lacrimal) glands, causing inflammation
• Hypersensitivity reactions – severe reactions, such as Stevens-Johnson syndrome and toxic epidermal necrolysis, can damage the surface of the eye and cause a long-term inflammation of the outer layer

Chemical, toxic, environmental and mechanical causes

Long-term exposure to certain chemicals, such as strong acids and alkalis present in household cleaning agents, chlorine, and also toxic agents in the environment, such as smoke or air pollution, can disrupt the tear film, which is what protects the outer layer of the eye. This can result in inflammation of the eye surface, causing keratoconjunctivitis.¹

In contact lens wearers, prolonged use, or inappropriately fitted or incorrectly maintained contact lenses can also cause mechanical irritation, which can lead to infection and inflammation of the eye surface.¹

Clinical presentation, history and examination of keratoconjunctivitis

As keratoconjunctivitis can be the result of a number of different causes, clinicians must undertake a careful evaluation of the patient to identify the potential cause.¹

Understanding if a person wears contact lenses, has any potential exposure to chemicals, eye drops, creams, or activities that may have resulted in foreign chemical, environmental or toxic agents entering the eye, is essential to rule out a potential toxic cause. 

In autoimmune and systemic cases, clinicians will ask about a history of disorder, including those such as rheumatoid arthritis, thyroid disease and Sjögren’s syndrome.¹

To rule out infectious causes, possible exposure to sick contacts will be questioned. In infectious cases, the redness will usually be seen all over the eye. In severe infective cases where damage to the cornea has occurred, ulceration of the cornea will be seen on examination.¹

Clinicians may also perform special tests such as the Schirmer test. This measures tear production, which is reduced in keratoconjunctivitis. Additionally, they may observe the eye through a slit-lamp to assess for long-term changes within the eye. If infectious causes are suspected, a swab may be used to take a sample from the conjunctiva or cornea to test for a potential bacterial, viral or fungal cause.¹³

Keratoconjunctivitis requires a detailed history and examination to diagnose and identify the subtype. This is essential for prompt identification, as timely and appropriate management is crucial to prevent long-term complications and eye damage.

Treatment and management of keratoconjunctivitis

Management of keratoconjunctivitis is dependent on a thorough evaluation to identify the underlying trigger. Some treatment options include artificial tears to relieve symptoms of dry eye and thicker ointments to be used during sleep. Warm or cold compresses can also be used over the eyelids to lubricate the eye and ease symptoms.

When keratoconjunctivitis is caused by an adenoviral infection, there is no definitive or approved antiviral therapy. Management is therefore primarily supportive, focusing on relieving symptoms and promoting recovery. Because viral cases are highly contagious, strict hygiene measures and infection control practices are essential to prevent transmission and recurrence.³

In bacterial keratoconjunctivitis, smear or culture samples should be collected to identify the causative organism. Empirical broad-spectrum antibiotic therapy should be initiated promptly and later adjusted to a targeted regimen based on microbiological results. Antibiotics are usually administered as topical eye drops or ointments.⁶

In fungal keratoconjunctivitis, topical antifungal treatments will be used. The treatment regimen is quite intensive, usually given hourly for the first 48 hours, and can continue for 12 weeks. In severe cases, oral or intravenous antifungals will be prescribed.⁷ 

In allergic keratoconjunctivitis, topical or systemic antihistamines will be used for symptom relief. Non-steroidal anti-inflammatory drops may also be used. Sometimes, corticosteroids are given to control severe inflammation.¹⁰

For autoimmune conditions, immunosuppressive therapies are the mainstay of treatment to modulate the immune response. Topical corticosteroids or other anti-inflammatory agents may also be employed to manage ocular inflammation.¹²

Summary

Keratoconjunctivitis is an inflammatory condition involving the conjunctiva and the corneal surface that together form the clear outer layer of the eye. It can be triggered by a wide range of factors, broadly classified as infectious or non-infectious in origin, with the latter including allergic, autoimmune, and toxic causes.

Evaluation of this condition requires a comprehensive ocular examination, supported by appropriate investigations and specialised tests to determine the underlying cause and severity. Accurate diagnosis is essential to guide effective management and prevent potentially sight-threatening, long-term complications.