Choroidal Osteoma: Causes, Symptoms, and Treatment

Choroidal osteoma is a rare, non-cancerous growth composed of mature bone tissue that forms within the choroid, a vascular layer located beneath the retina in the eye. This condition is considered benign, meaning it does not spread like cancer. While its presence can affect vision, it is not life-threatening.

Causes and Characteristics

The choroid is a layer of blood vessels and connective tissue situated between the retina, which senses light, and the sclera, the outer white part of the eyeball. Its primary role involves supplying oxygen and nutrients to the outer layers of the retina. A choroidal osteoma represents an abnormal development where mature bone tissue replaces portions of this vascular layer.

The exact reason a choroidal osteoma develops remains largely unknown, often referred to as idiopathic. It is not considered a hereditary condition. These tumors are most frequently observed in healthy young adult women, presenting in their second or third decade of life.

Choroidal osteomas usually affect only one eye, occurring unilaterally in about 75% of cases, but can appear in both eyes in 25% of individuals. The growth commonly forms near the optic nerve (juxtapapillary or peripapillary area), sometimes extending into the central vision area (macula). Clinically, these lesions appear yellow-orange and exhibit well-defined scalloped or geographic margins. Their size can vary, ranging from 2 to 22 millimeters in basal dimension and 0.5 to 2.5 millimeters in elevation.

Symptoms and Diagnosis

Many individuals with choroidal osteoma experience no symptoms, and the condition is often discovered incidentally during a routine dilated eye examination. When symptoms do occur, they are related to the tumor’s size or its location, especially if it affects the macula. Common visual disturbances include blurred vision, distorted vision (metamorphopsia), and the presence of blind spots or visual field defects.

An ophthalmologist conducts a thorough examination to detect and characterize a choroidal osteoma. Initial assessment involves ophthalmoscopy, where the doctor observes the yellowish lesion with scalloped edges and possible pigment clumping on its surface. To confirm the bony nature of the growth, B-scan ultrasonography is used. This imaging technique reveals a highly reflective lesion with a distinct “shadowing” effect behind it, indicating a dense, calcified structure.

Optical coherence tomography (OCT) provides detailed cross-sectional images of the retina and underlying choroid. OCT can show the tumor’s internal structure, displaying a unique latticework pattern of reflectivity resembling spongy bone. Additional diagnostic tools include fundus photography, which documents the tumor’s size and shape. Fluorescein angiography involves injecting a dye into the bloodstream; in choroidal osteoma, this test shows slow dye penetration into the tumor and persistent late fluorescence. A computed tomography (CT) scan of the head may also be used to visualize the calcification.

Complications and Vision Impact

The primary concern for individuals with choroidal osteoma is its potential impact on vision over time. The most frequent and significant complication is the development of choroidal neovascularization (CNV). This involves the growth of new, abnormal blood vessels from the choroid beneath the retina. These fragile vessels can leak fluid or blood, leading to significant vision loss and distortion if they affect the macula, the part of the retina responsible for sharp central vision.

Choroidal neovascularization is a common complication, with studies indicating it can occur in approximately one-third to nearly half of affected eyes. Beyond CNV, gradual changes in vision can also arise from other mechanisms. The tumor itself can slowly grow, which might affect overlying retinal tissue.

Another factor impacting vision is decalcification, a process where the bone material within the osteoma begins to break down. This decalcification can lead to thinning and atrophy of the overlying retinal pigment epithelium, a layer that supports the photoreceptor cells responsible for sight. If decalcification occurs under the fovea, the most sensitive part of the macula, it can cause poor long-term visual acuity. Subretinal fluid can also accumulate even without CNV, contributing to visual impairment. Overall, the visual prognosis varies, with a significant probability of legal low vision over time.

Management and Treatment Approaches

For many individuals diagnosed with choroidal osteoma, especially if the tumor is asymptomatic and not causing immediate vision problems, the most common approach involves regular monitoring. This observational strategy includes periodic comprehensive eye examinations and specialized imaging tests to track any changes in the tumor’s size, characteristics, or the development of new complications. The goal is to detect any concerning developments early.

Intervention becomes necessary when complications arise, especially the formation of choroidal neovascularization (CNV). The primary treatment for CNV associated with choroidal osteoma involves intravitreal anti-VEGF injections. These medications are injected directly into the eye to block vascular endothelial growth factor (VEGF), a protein that promotes the growth of abnormal blood vessels. Anti-VEGF injections work to stop the leakage from these new vessels and can lead to significant improvement or stabilization of vision.

Anti-VEGF therapy has shown high rates of success, with studies indicating complete or partial remission of CNV in a large percentage of treated eyes. While anti-VEGF injections are the preferred first-line treatment, photodynamic therapy (PDT) is another option that may be considered. PDT involves injecting a light-sensitive drug into the bloodstream, which is then activated by a specific laser light directed at the tumor. This process helps to close off the abnormal blood vessels and can cause the osteoma itself to regress. Some research suggests combining PDT with anti-VEGF injections might have synergistic effects, potentially reducing the need for frequent injections.

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