When most people hear the word “eye infection”, most think of pink eye. However, there is another type of eye infection that occurs beneath the surface of the eye called uveitis.
Uveitis is an inflammatory infection causing red eyes, blurry vision, light sensitivity, and pain on eye movement.
Before we get too far into understanding uveitis, it will be helpful to understand some basic eye anatomy.
The eye is a unique organ because it must remain transparent so that its structures do not interfere with the passage of light in or out of the eye.
This is because the specialized light-detecting cells are located on the innermost layer of the eye called the retina.
To form an image, light must properly be bent (i.e. refracted) through the front structures of the eye and reach the back of the eye as a point source. Once detected, the retinal cells transmit the information to the brain via the optic nerve for processing.
If normal bodily functions such as blood vessels, lymphatic drainage, and irregularly spaced cells coursed through the eye, it would interfere with the passage of light and thus create black spots (blind spots) in vision.
To combat this, the eye has a very unique anatomy. All of its cells are uniformly spaced so that light is not reflected off of them. Additionally, blood is ultra-filtered so that only necessary nutrients and cells can enter the eye.
This ultra-filtered blood can also only enter the eye at two points–in the retina and near the equator as aqueous humor. These two locations are respectively called the blood-retinal-barrier and the blood-aqueous-barrier.
The retina is the one part of the inner eye that has blood vessels coursing throughout. This is because the retina is composed of 10 individual layers, with blood vessels located in the deeper layers to provide nutrition to the more superficial layers.
The blood vessels in the retina must be uniformly placed–we do not want new blood vessel growth in the retina. If new blood vessel growth occurs in the retina, it is often not correctly located in the deep layers and can interfere with vision.
However, blood vessels are also unique in the retina because they contain tight junctions–special connections between the vessel wall cells that do not let anything leak into or out of the blood vessel. These tight junctions are what create the blood-retinal-barrier–a barrier that keeps unwanted blood from leaking out into the retina.
In comparison to the retinal blood vasculature, the vasculature that provides nutrition to the middle of the eye is even more complex.
The center structures of the eye (the lens, inner layers of the cornea, etc.) need nutrition too, but blood is too dark in color and would interfere with vision if it was able to course freely through the eye.
To combat this, blood near the equator of the eye is ultra filtered through the ciliary body to form the aqueous humor. Aqueous humor is a clear liquid containing only the needed nutrients for the eye.
The aqueous humor enters the eye near the equator by the lens, and then flows forward to exit the eye through the drainage system (trabecular meshwork). It is responsible for creating eye pressure.
Like the retinal blood supply, the vessels providing aqueous humor are also lined with tight junctions so that unwanted material, such as red blood cells and inflammatory cells, cannot enter the eye. These tight junctions are what create the blood-aqueous-barrier–a barrier that keeps blood and other opaque materials out of the aqueous humor.
Other important structures to note in the eye are the lens, iris, and the trabecular meshwork.
The lens is a clear structure located in the middle of the eye. It is flexible to allow us to view objects at different lengths (i.e. at distance, intermediate, and near).
The iris is the colored part of the eye. It is thin and flexible to allow the pupil to dilate and constrict, depending on how much light there is or what target you are looking at.
The trabecular meshwork is the drainage system of the eye. It is made up of several channels of tiny pores in which aqueous humor flows out of to re-enter the blood venous system.
Uveitis is a condition in which inflammation is upregulated in the ciliary body (the part that forms the aqueous humor). This inflammation can be acutely upregulated in the ciliary body, or sometimes this inflammation stems from high amounts of inflammation elsewhere in the body, becoming so great that it spills into the ciliary body and subsequently results in a temporary breakdown of the blood-aqueous-barrier.
Inflammation can be painful. This is why many individuals with acute uveitis will feel an achy, throbbing pain within the eye, especially when moving the eye around (i.e. looking left, right, up, or down).
Initially, inflammation of the ciliary body can cause a decrease in the amount of aqueous humor produced. This is noted in some individuals as a minor decrease in eye pressure.
Not only that, but inflammatory cells are white, fluffy, and sticky. When these cells infiltrate the aqueous humor, they can cause the surrounding structures (iris and lens) to become sticky.
In some cases, inflammatory cells can cause the structures to stick to one another through the formation of synechiae.
If the iris becomes sticky and attaches to the trabecular meshwork, it is called peripheral anterior synechiae (PAS).
If the lens or iris becomes sticky and attach to each other, it is called posterior synechiae (PS).
Synechaie can be dangerous because they interfere with the flow of aqueous humor. If the synechiae form a 360 degree circle, it can block off the flow of aqueous completely, resulting in pupillary block and a secondary condition called angle closure.
In angle closure, the aqueous humor is unable to flow from the ciliary body to the trabecular meshwork. This results in an accumulation of aqueous humor within the anterior chamber of the eye, henceforth increasing eye pressure which can be painful and vision threatening.
Symptoms of an acute angle closure include headache above the eyes (“brow ache”), nausea, vomiting, blurred vision, extreme light sensitivity, and dizziness.
Alternatively, uveitis can also increase eye pressure in the later stages of the infection due to leaked inflammatory cells in the aqueous humor clogging up the trabecular meshwork, making it more difficult to drain aqueous humor effectively.
While eye pressure secondary to trabecular meshwork dysfunction often does not become as high as in an angle closure, it can become elevated resulting in a browache, blurry or hazy vision, and light sensitivity.
While uncommon, chronically clogged trabecular meshwork secondary to inflammation from uveitis can lead to glaucoma–a disease in which increased eye pressure compresses the optic nerve, causing gradually progressive permanent vision loss.
Therefore, it is important to see an eye doctor and get the uveitis treated and eye pressure lowered back to normal as quickly as possible.
Is there anything that can be done to prevent uveitis from occurring?
Most cases of uveitis are idiopathic, meaning we do not know the cause of them. Sometimes the body just gets inflamed and there is no rhyme or reason as to why.
Other causes of uveitis, however, include conditions that increase inflammation throughout the body. These conditions include active infection (especially in the facial region including the mouth and ears), arthritis, ulcerative colitis, crohn’s disease, psoriasis, sarcoidosis, lupus, multiple sclerosis, AIDs, and Bechet’s disease.
There also seems to be some connection between some uveitis cases and COVID-19 infections, as well as a rare adverse reaction to the COVID-19 vaccines. Although, this information is still rather new and is currently being researched so the exact connection between the two is still unknown.
If you believe you may have uveitis, or have been diagnosed with uveitis, it is important to discuss any of the above conditions with your eye doctor so that he/she can treat you appropriately. You may need to have the systemic condition treated in addition to the uveitis to decrease the underlying cause of the increased inflammation throughout the body.
Typically uveitis cases are treated with steroid eye drops to reduce inflammation within the eye. Your doctor may also prescribe a cycloplegic–an eye drop that keeps the eye dilated, to help with pain from the iris moving around and stirring up more inflammation.
With proper treatment, a course of uveitis can last anywhere from a few weeks to a few months. Your doctor will want to monitor progress regularly to watch for changes in eye pressure and ensure inflammation is decreasing over time.
In some individuals, uveitis can become a chronic issue. It may recur during times of stress or concurrently with flare-ups in systemic conditions.
If uveitis is recurring and you have not been diagnosed with a systemic disorder, your eye doctor may recommend blood work testing to ensure there is not an underlying mechanism responsible for the frequent recurrences.
Regardless of the cause, uveitis can be a serious condition if not managed appropriately. If you, or someone you know, is suffering from red, achy, light sensitive eyes, be sure to give our office a call today!