Focal choroidal excavation (FCE) is an unusual anatomical finding defined as a localized, inward indentation or concavity of the choroid. The choroid is the vascular layer between the retina and the sclera, supplying nourishment to the outer retinal layers. FCE typically manifests as an isolated pit in the macula, the central area of the retina responsible for sharp, detailed vision. This diagnosis is made exclusively through advanced imaging, as the lesion often appears subtle during a standard eye examination.
What Defines the Excavation
FCE is distinguished by how the overlying retinal tissue interacts with the choroidal depression. This structural classification determines the patient’s visual experience and long-term prognosis. The two main structural subtypes are conforming and non-conforming, based on the relationship between the retina and the recessed choroid.
The conforming type occurs when the outer retinal layers remain attached to the underlying retinal pigment epithelium (RPE) and follow the inward contour of the excavation. The retinal structure is draped into the dip, with no separation between the photoreceptor outer segments and the RPE. This arrangement is associated with stable vision and few visual symptoms because the light-sensing mechanism remains structurally intact.
Conversely, the non-conforming type presents with a distinct separation between the outer retinal layers and the RPE, creating a hyporeflective space. This gap is presumed to contain subretinal fluid, which disrupts normal photoreceptor function. Detachment of photoreceptor tips from the nourishing RPE layer leads to greater visual disturbance, such as metamorphopsia or blurred vision. This less stable subtype warrants careful clinical monitoring.
The excavation’s shape can be characterized as cone-shaped, bowl-shaped, or a mixed configuration. The location of the excavation—whether it affects the fovea (the center of the macula) or an adjacent area—further contributes to the clinical definition and potential impact on visual acuity.
Potential Factors Behind FCE Development
The exact mechanism causing FCE formation remains uncertain, but research suggests it relates to conditions affecting choroidal thickness and structure. While some cases are idiopathic, FCE is frequently observed in eyes belonging to the pachychoroid spectrum of diseases. This spectrum encompasses conditions characterized by an abnormally thickened choroid, typically measuring over 300 micrometers.
A distinguishing feature of pachychoroid conditions is the presence of dilated outer choroidal vessels, known as pachyvessels, in the Haller’s layer. These large vessels are thought to cause congestion, which may compress the overlying choriocapillaris, the innermost layer of the choroid responsible for retinal nourishment. This chronic congestion and subsequent localized ischemia may contribute to the RPE dysfunction and structural changes leading to the excavation.
The localized indentation may be a congenital malformation, representing an inherent weakness in the tissue structure. However, FCE is also observed as an acquired entity, sometimes developing after inflammation or scarring from other retinal diseases. Conditions like Central Serous Chorioretinopathy (CSCR) and Choroidal Neovascularization (CNV) are commonly associated with FCE, supporting the theory of an underlying choroidal vascular disturbance.
The theory suggests that localized thickening and abnormal fluid dynamics in the pachychoroid may create mechanical stress, pulling the RPE-Bruch’s membrane complex inward. This inward pull, possibly combined with localized choroidal thinning, results in the characteristic pit. The frequent occurrence of the excavation in areas of choroidal hyperpermeability seen on angiography highlights the likely involvement of faulty choroidal circulation.
Advanced Imaging for Diagnosis
The identification and classification of FCE rely almost entirely on specialized ophthalmic imaging, as the condition is often invisible during a traditional fundus examination. Optical Coherence Tomography (OCT) is the definitive diagnostic tool for visualizing FCE. OCT uses light waves to capture high-resolution, cross-sectional images of the retina and the underlying choroid, providing a microscopic view of the eye’s layers.
This technology allows clinicians to precisely measure the depth and width of the choroidal concavity, quantifying the severity of the lesion. OCT provides the necessary detail to differentiate between the conforming and non-conforming subtypes by clearly revealing the presence or absence of separation between the outer retina and the RPE. The image confirms the excavation by showing the RPE band dipping down into the choroid, without features of other conditions like posterior staphyloma or scleral ectasia.
To obtain a clearer view of deep choroidal structures, Enhanced Depth Imaging OCT (EDI-OCT) is frequently employed. EDI-OCT is a modified scanning technique that focuses the imaging light further back, providing superior visualization of the outer choroid and the scleral interface. This enhanced view helps confirm the presence of pachyvessels and overall choroidal thickening, linking FCE to the pachychoroid spectrum. OCT’s ability to non-invasively confirm the diagnosis and define the subtype makes it the gold standard for management.
Monitoring and Visual Outcomes
For many patients, FCE is an incidental finding, especially in the conforming type, where visual acuity remains stable. Patients with this type are frequently asymptomatic because the retina’s functional layers are not significantly disrupted. The standard approach for these stable conforming lesions is periodic observation and regular monitoring using OCT scans.
Visual symptoms, when they occur, are usually mild and may include slight vision distortion (metamorphopsia) or blurred vision. These symptoms are more common with non-conforming FCE or when the excavation is located directly beneath the fovea. The hyporeflective space in non-conforming FCE, which represents fluid accumulation, is responsible for the visual compromise.
The primary concern in managing FCE is the development of associated complications that can negatively impact vision. FCE increases the risk of developing choroidal neovascularization (CNV), which is the growth of abnormal blood vessels that can leak and cause severe vision loss. It is also associated with the recurrence or persistence of Central Serous Chorioretinopathy (CSCR), a condition involving fluid buildup beneath the retina.
When complications such as CNV or persistent subretinal fluid arise, treatment focuses on managing the complication rather than the excavation itself. Interventions may include laser therapy or anti-vascular endothelial growth factor (anti-VEGF) injections to treat the abnormal blood vessel growth. In the absence of such complications, the condition is typically non-progressive, and the long-term visual prognosis remains favorable, provided regular monitoring is maintained.