Eye inflammation has dozens of possible causes, ranging from infections and autoimmune conditions to physical injuries and environmental exposures. The most common form, uveitis, affects roughly 213 out of every 100,000 people in the United States based on data spanning 2013 to 2023. Understanding where the inflammation occurs and what triggered it determines how serious it is and how it gets treated.
Where Inflammation Occurs in the Eye
The eye has multiple layers and chambers, and inflammation can settle into any of them. The location matters because it points toward different causes and carries different risks to your vision.
Uveitis, the umbrella term for inflammation of the eye’s middle layer, is classified into four types based on location. Anterior uveitis affects the front chamber of the eye and is the most common form. Intermediate uveitis targets the gel-like substance (vitreous) filling the center of the eye. Posterior uveitis involves the choroid, a blood vessel layer at the back of the eye near the retina. Panuveitis means inflammation has spread across multiple areas at once.
But uveitis isn’t the only kind of eye inflammation. Scleritis and episcleritis affect the white outer wall of the eye. Keratitis targets the cornea. Conjunctivitis involves the thin membrane lining the eyelid and white of the eye. Each condition has its own set of triggers.
Infections That Inflame the Eye
Infections are one of the most straightforward causes. A pathogen invades the eye tissue, and your immune system responds with inflammation to fight it off. The three most common infectious triggers are toxoplasmosis (a parasitic infection), herpes simplex virus, and varicella-zoster virus, the same virus responsible for chickenpox and shingles.
Less common but well-documented infectious causes include syphilis, tuberculosis, Lyme disease, histoplasmosis (a fungal infection), and bartonellosis (cat scratch disease). In people with weakened immune systems, cytomegalovirus and certain fungal organisms like Pneumocystis can cause significant eye inflammation that would rarely occur in otherwise healthy individuals.
Rarer still, viruses like dengue, West Nile, Zika, chikungunya, and even Ebola have been linked to uveitis. Fungal infections from Candida and Aspergillus can also reach the eye, typically through the bloodstream in hospitalized or immunocompromised patients.
Autoimmune and Systemic Diseases
Many cases of eye inflammation aren’t caused by an outside invader at all. Instead, the immune system mistakenly attacks the eye’s own tissues. This can happen as an isolated event or as part of a body-wide autoimmune condition.
Rheumatoid arthritis is a well-known example. It can trigger a surprisingly long list of eye problems: dry eye, scleritis, episcleritis, uveitis, retinal vasculitis (inflamed blood vessels in the retina), and in rare cases, a serious condition called peripheral ulcerative keratitis that can lead to vision loss if not treated promptly.
Sjögren’s syndrome, a chronic inflammatory disease that primarily attacks moisture-producing glands, causes eye problems in about one in three patients. Thirteen percent of those cases are sight-threatening. Dry eye disease is the most common symptom, but episcleritis, scleritis, retinal vasculitis, and corneal damage can also develop. Notably, about 1 in 10 Americans over 50 who are diagnosed with dry eye disease turn out to have underlying Sjögren’s syndrome.
Other systemic conditions frequently linked to eye inflammation include lupus, psoriasis, scleroderma, and a group of spinal and joint conditions called spondyloarthropathies. Sarcoidosis, an inflammatory disease that forms tiny clumps of cells in organs throughout the body, is another common culprit behind uveitis.
Chemical and Physical Injuries
Trauma to the eye triggers inflammation as part of the body’s natural healing response. A scratch on the cornea, a blow to the eye, or a foreign object lodged under the eyelid can all set off a cascade of swelling, redness, and pain.
Chemical exposure is particularly dangerous. Acid burns damage the eye by denaturing proteins on contact, and the coagulated tissue actually forms a barrier that limits deeper penetration. Alkali burns are worse because they don’t create that barrier and can keep destroying tissue as they seep inward. One notable exception among acids is hydrofluoric acid, where fluoride ions penetrate the full thickness of the cornea rapidly and cause severe destruction of the front of the eye.
A detail that catches many people off guard: tiny chemical particles can become trapped under the eyelids or in the folds of the conjunctiva, causing continued chemical exposure long after the initial splash. This is why thorough flushing with water is critical after any chemical contact with the eye.
Medications and Smoking
Certain medications can trigger eye inflammation as a side effect. Bisphosphonates (used for osteoporosis), some anti-epileptic drugs, biologic therapies, and certain cancer treatments have all been linked to scleritis and other forms of ocular inflammation.
Smoking is an independent risk factor. It can directly contribute to uveitis by irritating the uveal layer of the eye, leading to redness, pain, and vision problems. Smoking also worsens thyroid eye disease, a condition where the immune system attacks tissues around the eyes, causing swelling and bulging. For people already at risk of eye inflammation due to an autoimmune condition, smoking adds fuel to the fire.
Symptoms That Signal an Emergency
Not all eye inflammation is urgent, but certain symptoms require immediate attention. Sudden painless loss of vision in one eye can indicate a blocked blood vessel in the retina, which is a time-sensitive emergency. A sudden burst of flashing lights and floaters in one eye, especially with a shadow or curtain effect across your visual field, may signal a retinal tear or detachment.
After a chemical splash, decreased vision combined with a cloudy cornea or white, bloodless-looking conjunctiva indicates a serious burn. Following any blunt or sharp trauma, warning signs include a misshapen pupil, visible blood pooling in the front of the eye, or a shallow-looking anterior chamber compared to the other eye.
For more typical inflammatory conditions like anterior uveitis, the hallmark symptoms are a red, painful eye, sensitivity to light, and blurred vision. These develop over hours to days rather than seconds, but they still warrant prompt evaluation because untreated uveitis can lead to permanent vision damage, including glaucoma, cataracts, and swelling of the retina.
Why Identifying the Cause Matters
Eye inflammation is a symptom, not a diagnosis. Treatment depends entirely on what’s driving it. An infection needs antimicrobial therapy targeting the specific organism. Autoimmune-related inflammation requires suppressing the immune response, sometimes with long-term immunosuppressive treatment. Episcleritis, on the milder end, often resolves on its own or with simple anti-inflammatory drops. Scleritis, by contrast, typically needs oral steroids and longer-term immune-suppressing therapy.
When eye inflammation keeps coming back or doesn’t respond to initial treatment, it often signals an underlying systemic condition that hasn’t been identified yet. Blood work, imaging, and sometimes testing of fluid from inside the eye help narrow down the cause. Roughly 30 to 50 percent of uveitis cases end up being classified as idiopathic, meaning no specific cause is found despite thorough investigation.