Uveitis is inflammation of the middle layer of the eye, a condition that affects millions of people worldwide and can lead to serious complications if left untreated. Understanding this eye condition, its causes, and how it develops is essential for protecting your vision.
What is Uveitis?
Uveitis refers to inflammation, or swelling and irritation, of the uvea, which is the middle layer of tissue inside your eye. The uvea itself consists of three distinct parts that work together to help your eye function properly. These parts include the iris, which is the colored circle you see when you look in the mirror; the ciliary body, a structure behind the iris that helps your lens focus on objects; and the choroid, a layer filled with blood vessels that brings nutrients to the retina at the back of your eye.[1]
When inflammation occurs in any of these three structures, doctors classify it as uveitis. The condition can affect just one eye or both eyes at the same time, and it may appear suddenly or develop gradually over time. The inflammation itself happens when your immune system responds to what it perceives as a threat. Sometimes this immune response is fighting an actual infection in your eye, but other times your immune system mistakenly attacks healthy tissue in your eyes, causing damage even when there is no infection present.[3]
One important aspect of uveitis that makes it particularly concerning is the limited space inside your eyeball. Because there is not much room for tissues to swell, even small amounts of inflammation can change the shape of your eye. Your eye shape plays a critical role in how you see, and even tiny changes from swelling can disrupt your vision. This is why uveitis needs prompt attention from an eye care specialist.[1]
Types of Uveitis
Medical professionals organize uveitis into several categories based on which part of the eye is primarily affected by inflammation. The most common type is anterior uveitis, which affects the front part of the eye, specifically the iris and ciliary body. This form is generally less serious than other types and often causes visible symptoms that you or others can notice, such as redness or changes in pupil shape.[3]
Intermediate uveitis affects the middle portion of the eye, particularly the ciliary body and the vitreous, which is the gel-like fluid that fills the center of your eyeball. This type often occurs in young adults who may have other specific health conditions like multiple sclerosis or sarcoidosis.[4]
Posterior uveitis is the rarest form and involves inflammation at the back of the eye, affecting the retina and choroid. The retina is the light-sensitive layer that lines the inside back of the eye, sending visual information to your brain. When inflammation occurs in this area, the symptoms are usually more subtle to outside observers but can significantly affect what you see and how well you see it.[3]
Finally, panuveitis represents the most extensive form of the condition, where inflammation affects all parts of the uvea, from the front to the back of the eye. This widespread inflammation can be particularly challenging to manage and may require more aggressive treatment approaches.[1]
Epidemiology
Uveitis is a common eye condition that affects people around the world. Globally, approximately 4 million new cases occur each year, making it a significant cause of eye-related health concerns. In the United States alone, estimates suggest that between 80,000 and 168,000 new cases are diagnosed annually.[1]
The condition most commonly affects adults, with the likelihood of developing uveitis increasing with age. Research shows that people between the ages of 20 and 60 are at highest risk, though anyone at any age can develop the condition. Children account for only a small percentage of cases, representing somewhere between 2% and 20% of all uveitis diagnoses. This means that while children can certainly develop uveitis, it is primarily a condition that affects working-age adults and older individuals.[1][3]
When looking at gender differences, women appear to be slightly more likely to develop uveitis than men, though the difference is not dramatically large. This pattern holds true across different populations and geographic regions.[5]
Causes of Uveitis
The causes of uveitis are diverse and, in many cases, remain unknown. Between 50% and 70% of uveitis cases are classified as idiopathic, which means that even after thorough examination and testing, doctors cannot identify a specific cause that can be seen or measured. In these situations, the inflammation occurs for reasons that medical science does not yet fully understand.[1]
When a cause can be identified, infections represent one major category. Various types of germs, or pathogens, can enter your body and trigger inflammation in the eye. Viral infections are particularly common culprits, including herpes simplex virus (the virus that causes cold sores), varicella-zoster virus (which causes chickenpox and shingles), and cytomegalovirus. Vaccine-preventable diseases like rubella can also lead to uveitis, highlighting the importance of maintaining up-to-date immunizations.[1]
Bacterial infections can also cause uveitis. The bacteria responsible for serious diseases like syphilis and tuberculosis are known to trigger eye inflammation in some people. Fungal infections, including those caused by Candida species (which cause candidiasis or yeast infections) and mold species like Aspergillus, represent another infectious pathway to developing uveitis. Even parasites can be responsible, including those you might contract from pets, particularly cats, which can transmit organisms that cause toxoplasmosis.[1][3]
Beyond infections, autoimmune diseases are another significant cause of uveitis. These are conditions where your immune system mistakenly attacks your own healthy tissues. Many different autoimmune conditions have been linked to uveitis, including AIDS, ankylosing spondylitis, Behcet’s disease, lupus, multiple sclerosis, psoriasis, rheumatoid arthritis, sarcoidosis, ulcerative colitis, and Vogt-Koyanagi-Harada disease. When someone with one of these conditions develops uveitis, the eye inflammation is part of their broader systemic illness.[3]
Eye injuries and trauma can directly cause uveitis by damaging the uveal tissue or introducing infection into the eye. Even eye surgery, while performed to help vision, can sometimes trigger inflammatory responses that lead to uveitis. In rare cases, certain medications have been associated with developing this condition. Additionally, cancers that can affect the eye, such as lymphoma, may present with or cause uveitis.[4]
Risk Factors
While anyone can develop uveitis, certain factors increase the likelihood that you will experience this eye condition. One of the most significant modifiable risk factors is cigarette smoking. People who smoke cigarettes have a notably higher risk of developing uveitis compared to non-smokers. This provides a compelling reason to quit smoking or avoid starting in the first place, as it directly impacts your eye health.[3]
Having an existing autoimmune disease substantially increases your risk of developing uveitis. If you have been diagnosed with conditions like rheumatoid arthritis, lupus, ankylosing spondylitis, psoriasis, inflammatory bowel disease including ulcerative colitis or Crohn’s disease, multiple sclerosis, or sarcoidosis, you should be aware that eye inflammation is a possible complication. Regular communication with both your primary care doctor and an eye specialist can help catch uveitis early if it develops.[3]
People with certain infections or a history of specific infections are also at increased risk. If you have had or currently have herpes simplex, shingles, syphilis, tuberculosis, Lyme disease, toxoplasmosis, or HIV/AIDS, your chances of developing uveitis are elevated. Some of these infections can directly invade the eye, while others may trigger immune responses that lead to inflammation.[3]
A history of eye injury or recent eye surgery also places you at increased risk. Any trauma to the eye can disrupt the normal structures and potentially trigger inflammation. Similarly, while eye surgery is carefully performed with sterility in mind, the body’s response to surgical intervention can sometimes include unwanted inflammation.[4]
Symptoms of Uveitis
The symptoms of uveitis vary depending on which part of your eye is affected by inflammation. Understanding these symptoms is important because recognizing them early can lead to faster treatment and better outcomes for your vision.
Anterior uveitis, which affects the front of the eye, typically causes symptoms that are readily noticeable to you and to others looking at your eye. The most common symptom is eye pain, which can range from mild discomfort to severe aching. Your eye may appear red or irritated, with the white part of the eye taking on a pink or red color. You may experience photophobia, which means your eyes become extremely sensitive to light, making it uncomfortable to be in bright environments or look at light sources. Your vision may become blurred, making it difficult to see clearly. The tissue covering the white part of your eye, called the conjunctiva, may become swollen.[1]
In more severe cases of anterior uveitis, you might notice that your pupil changes from its normal round shape to an irregular shape. Some people develop a visible accumulation of white fluid at the bottom of the front of the eye, a sign called hypopyon, or notice a ring of white material around the iris. These visible changes can be alarming but are important indicators that you need immediate medical attention.[1]
Intermediate and posterior uveitis present differently because the inflammation occurs in areas that are not visible from the outside of your eye. Instead of visible redness or external changes, these types primarily affect your vision itself. A very common symptom is an increase in floaters, those small dark spots or squiggly lines that seem to float across your field of vision. You might notice that floaters you already had become more prominent or that new ones appear. Some people experience gaps or missing sections in their visual field, meaning certain areas of their vision seem blank or absent. Overall decreased vision, where everything appears dimmer or less clear, is another common symptom of inflammation in the middle or back of the eye.[1]
Symptoms often come on suddenly and worsen quickly, though in some cases they develop more gradually over time. The condition can affect just one eye or both eyes simultaneously. Interestingly, some people, particularly children and young adults, may not experience any symptoms at all, with uveitis only discovered during a routine eye examination.[2][4]
Prevention
While not all cases of uveitis can be prevented, especially those that occur for unknown reasons or as part of autoimmune diseases, there are steps you can take to reduce your risk and protect your eye health.
One of the most important preventive measures is quitting smoking if you currently smoke, or never starting if you do not. Smoking is a significant modifiable risk factor for uveitis, meaning it is something within your control that directly affects your chances of developing this condition. By eliminating tobacco use, you not only reduce your risk of uveitis but also improve your overall health in numerous other ways.[3]
Maintaining current vaccinations is another important preventive strategy. Because some vaccine-preventable diseases like rubella can cause uveitis, staying up to date with recommended immunizations helps protect you from these infectious causes. This is particularly important for children, who should receive all standard childhood vaccinations according to their healthcare provider’s schedule.
If you have an autoimmune disease, inflammatory condition, or chronic infection that is known to be associated with uveitis, working closely with your healthcare providers to manage that condition effectively may help reduce your risk of developing eye complications. Taking medications as prescribed, attending regular follow-up appointments, and reporting any new symptoms promptly are all important aspects of managing chronic conditions that could affect your eyes.
Protecting your eyes from injury is another preventive measure. Wearing appropriate safety glasses or goggles when engaging in activities that could harm your eyes, such as certain sports, construction work, or working with chemicals, can prevent trauma that might trigger uveitis. If you own cats or handle cat litter, practice good hygiene including washing your hands thoroughly, as this can reduce your risk of parasitic infections like toxoplasmosis that can lead to eye inflammation.[1]
Regular eye examinations are not exactly prevention, but they are crucial for early detection. Even if you have no symptoms, routine eye exams can sometimes identify early signs of uveitis or other eye conditions before they cause noticeable problems or permanent damage. This is especially important if you have risk factors like autoimmune disease or a history of eye problems.[2]
Pathophysiology
Understanding what happens in your body when uveitis develops helps explain why the symptoms occur and why prompt treatment is so important. The fundamental problem in uveitis is inflammation, which is your body’s natural response to perceived threats, whether those threats are real infections or mistaken attacks on healthy tissue.
When inflammation occurs in the uvea, several physical and biochemical changes take place. Blood vessels in the affected area become more permeable, meaning they allow fluid and immune cells to leak out into the surrounding tissues. This process causes the swelling that characterizes inflammation. In the eye, where space is extremely limited and precision is essential for vision, this swelling can have significant consequences.[3]
In anterior uveitis, inflammation of the iris and ciliary body leads to the accumulation of inflammatory cells in the fluid-filled space at the front of the eye. These cells can be seen by eye doctors using specialized microscopes. The inflammation can cause the iris to stick to other structures in the eye, potentially changing pupil shape and affecting how light enters the eye. The ciliary body’s inflammation can affect its ability to produce the clear fluid that fills the front of the eye, potentially altering eye pressure.[6]
When inflammation affects the vitreous in intermediate uveitis, immune cells and inflammatory proteins accumulate in this gel-like substance. This accumulation is what causes the appearance of floaters, as these cells and proteins cast shadows on the retina. The inflammation can also cause the vitreous to become hazy, reducing visual clarity.[1]
Posterior uveitis involves inflammation of the choroid, the blood vessel-rich layer beneath the retina, and sometimes the retina itself. The choroid’s job is to supply oxygen and nutrients to the outer layers of the retina, so when it becomes inflamed, this critical supply can be disrupted. The inflammation can cause fluid to leak from blood vessels, potentially leading to retinal swelling or detachment. If the retina itself becomes inflamed, the light-sensitive cells that detect visual information can be damaged, directly impacting vision.[4]
The eye shape is crucial for proper vision because light must be focused precisely on the retina for clear images. Even small amounts of swelling from inflammation can alter the eye’s shape enough to distort vision. Additionally, chronic or severe inflammation can lead to permanent structural changes, including the formation of scar tissue, which does not function like normal eye tissue and can permanently impair vision.[1]
Several complications can arise from the pathophysiological changes of uveitis. Macular edema, or swelling of the central part of the retina called the macula, can occur when fluid accumulates in this critical area for detailed vision. Glaucoma, characterized by increased pressure inside the eye, can develop if inflammation affects fluid drainage or if inflammatory cells physically block drainage channels. Cataracts, or clouding of the lens, can form as a result of chronic inflammation or as a side effect of treatments like steroids. Damage to the optic nerve, which carries visual signals from the eye to the brain, can occur if inflammation spreads to this structure or if increased eye pressure compresses it. In severe cases, retinal detachment can occur, where the retina pulls away from its underlying support tissue.[4]
