What is Uvea?
The uvea is the vascular tunic of the eye, interposed between the sclera (external fibrous tunic) and the retina (internal nervous tunic). Anatomically, the uveal tract includes the iris, the ciliary body and the choroid.
The uvea is characterized by the presence of numerous blood and lymphatic vessels, which supply nutrients and oxygen to most of the ocular structures. For this reason, an inflammatory process affecting the uveal lining can also have consequences on the cornea, retina, sclera and other tissues of the eye.
The uvea also contains the intrinsic muscles of the eyeball that allow accommodation, and regulates the secretion and reabsorption of aqueous humor.
Com "is Done
The uvea is a predominantly vascular anatomical structure, located between the sclera (the white part of the eye) and the retina (the innermost membrane formed by photoreceptors, cells sensitive to light).
The uvea can be divided into three parts, respectively in the antero-posterior direction:
- Iris: ring of pigmented muscle tissue that widens and narrows, acting like a diaphragm, changing the diameter of the anterior opening (pupil);
- Ciliary body: includes the ciliary muscle, which allows the set of movements necessary to focus the observed image (accommodative process);
- Choroid: rich in blood vessels, it irrigates most of the tissues of the eyeball.
Iris
The iris is the anterior part of the vascular tunic and is the only component of the uvea to be visible through the cornea. This structure appears as a thin annular membrane, placed as a diaphragm in front of the lens (which acts as a lens). .
In the center, the iris has a central foramen, the pupil, whose diameter can be modified, thanks to the sphincter and dilator muscle, depending on the intensity of the light.
The iris is also responsible for the characteristic color of our eyes.
Ciliary body
The ciliary body begins at the sclerocorneal junction and extends up to the ora serrata which marks the limit with the rear choroid; its anterior portion (including the ciliary muscle and ciliary processes) is in relationship with the peripheral part of the " iris.
The ciliary body is the ocular structure responsible for both the production of aqueous humor and the control of accommodation (focusing of the images). Through the ciliary muscle, in fact, this part of the uvea acts by regulating the curvature of the lens, to which it is connected through the suspensory ligaments of the same (zonular fibers).
Choroid
The choroid is formed by an extensive network of blood vessels deriving from the ophthalmic artery. This portion of the uvea provides nourishment and oxygenation to the retina and sclera.
The choroid is also made up of melanocytes which, to varying degrees, impart different degrees of color to the fundus. These pigments have the important function of absorbing the light that reaches the back of the eye, preventing its reflection (a phenomenon that would cause distortions of the visual image).
Functions
The uvea performs the following functions:
- It represents the access route for the vessels that supply the eye;
- Adjust the amount of incoming light;
- It improves the contrast of the retinal image, reducing the reflection of light rays inside the eye;
- Secretes and reabsorbs the aqueous humor that circulates in the eyeball;
- Check the shape of the lens in the focusing process.
Many of these functions are under the control of the autonomic nervous system.
Diseases of the Uvea
Uveitis
Uveitis is inflammation of one of the components of the uveal tract (iris, ciliary body or choroid):
- When the uvea is inflamed in its anterior part, at the level of the iris, we speak of iritis (inflammation in the anterior chamber only) or iridocyclitis (inflammation in the anterior chamber and in the anterior vitreous);
- If the inflammation is localized in the intermediate part of the uvea (ciliary body) we speak, instead, of cyclitis;
- Finally, as regards the posterior part of the uvea (choroid), the following are distinguished on the basis of the localization of the initial inflammatory process: choroiditis, retinitis, chorioretinitis and retinocoroiditis.
The most common symptoms of uveitis include hypersensitivity to light (photophobia), oculodynia, eye redness, perception of floaters and reduced vision. Other manifestations depend on the location and severity of the inflammation. If neglected, uveitis can lead to severe vision consequences, including cataracts, glaucoma, retinal detachment, and permanent blindness.
Uveitis can result from various ocular and non-ocular infections (herpes simplex and zoster, mumps, toxoplasmosis, TB, syphilis, Lyme disease, etc.), trauma and systemic diseases, many of which are autoimmune. Possible causes include multiple sclerosis, sarcoidosis and various spondyloarthropathies. In many cases, however, uveitis is idiopathic, so the etiology remains unknown.
Treatment depends on the cause, but is usually based on the use of topical or intraocularly injected corticosteroids, combined with a cycloplegic-mydriatic drug, to reduce inflammation and pain. Severe and refractory cases may require the use of corticosteroids or systemic immunosuppressants. Infectious uveitis requires specific antimicrobial therapy.
- Panuveiti. When the inflammation is widespread and affects all the layers of the uvea simultaneously, it is called panuveitis.
- Endophthalmitis. Endophthalmitis is an acute panuveitis, resulting, more often than not, from the metastatic spread of bacterial, fungal and viral infections. This condition represents a "medical emergency, as the prognosis for vision is directly related to the time that elapses from" onset of inflammation upon treatment.
Most cases follow surgery and eye trauma. Sometimes, acute sterile endophthalmitis can also be observed, expression of hypersensitivity reactions.
This severe inflammation of the eyeball typically causes intense eye pain, conjunctival hyperaemia, and decreased vision. In some cases, untreated intraocular infections extend beyond the confines of the eye and involve the orbit and central nervous system.
Treatment involves intravitreal (and possibly intravenous) administration of broad spectrum antibiotics (eg vancomycin and ceftazidime). Thereafter, treatment must be adapted based on culture and antibiogram results. The use of intraocular corticosteroids (except for fungal endophthalmitis) and vitrectomy are sometimes considered. Visual prognosis is often poor. even with early and adequate treatment.
Congenital anomalies of the uvea
The congenital malformations of the eye affecting the iris, the ciliary body and the choroid include colobomas, ie slit-shaped lesions, resulting in more or less serious defects in vision. These conditions can occur sporadically or in the context of various genetic syndromes.
Tumors of the uvea
Uveal tumors include melanomas of the iris and, above all, those of the choroid. The damage caused by these neoplasms affects the visual function and the integrity of the eye. The uvea can also be the site of metastases, resulting, in particular , from breast or lung cancer.
Choroid melanoma
Choroid melanoma is the most common primary malignant intraocular tumor in adults.
The neoplastic process originates from choroidal melanocytes and can spread locally, internally infiltrating the bulb or the outermost orbital tissues. Choroid melanoma can also cause distant metastases.
The presentation of the disease occurs more often at an age between 50 and 60 years. Symptoms of choroid melanoma tend to develop late and are not specific; possible manifestations include: decreased visual acuity, visual field deficit, phosphenes (flashes of light, sometimes colored) and metamorphopsias (distorted vision). Other symptoms reported by patients can be attributed to a concomitant retinal detachment.
Diagnosis is based on fundus examination, supplemented, when indicated, by other tests, such as fluorangiography, bulbar ultrasound and CT.
Treatment varies depending on the location and size of the tumor. Small tumors are treated with laser, radiotherapy or brachytherapy in order to preserve visual function and save the eye. Local resection is rarely performed. Large tumors, on the other hand, require enucleation (removal of the entire eyeball).
Choroidal metastases
Since the choroid is richly vascularized, choroidal metastases are frequent, especially if they result from breast cancer in women and from lung and prostate cancers in men.
Sympathetic ophthalmia
Sympathetic ophthalmia (OS) is a rare anterior granulomatous uveitis that occurs after penetrating trauma, contusions or surgery to the contralateral eye (therefore not directly affected by the triggering event).
The etiology of the disorder has not yet been clarified. However, at the origin of the inflammatory process, an autoimmune reaction directed against the ocular auto-antigens formed following the initial lesion was found.
Usually, uveal tract inflammation occurs within 2-12 weeks. Symptoms typically include: floaters, pain, photophobia, accommodation paresis, metamorphopsia, and vision loss. Sympathetic ophthalmia is frequently associated with pathological processes affecting the posterior segment, including choroiditis, macular edema and exudative retinal detachment.
Treatment usually requires the administration of high-dose oral corticosteroids (for at least 3 months), combined with immunosuppressive drugs (cyclophosphamide, azathioprine or cyclosporine). Prompt wound closure decreases the risk of sympathetic ophthalmia.
