Posterior staphyloma is a progressive structural change in the eye, defined as an abnormal, circumscribed outpouching or bulging of the posterior wall of the globe. This condition is intrinsically linked to pathological myopia, a form of severe nearsightedness characterized by excessive elongation of the eye. The presence of a staphyloma is a significant indicator of a structurally compromised eye, predisposing it to a range of severe complications that can lead to permanent vision loss. Recognizing this abnormality is important because it signifies a substantially increased risk for vision-threatening diseases compared to simple high myopia. The resulting distortion of the eye’s shape stretches and thins the delicate inner layers.
Pathophysiology and Classification
Posterior staphyloma develops as a direct consequence of extreme axial elongation, where the eyeball grows too long from front to back, a defining characteristic of high myopia. This excessive stretching places immense mechanical stress on the sclera, the tough outer white layer of the eye, causing it to thin and weaken in the posterior segment. The biomechanical failure in this weakened area leads to a localized, concave bulge—the staphyloma—which possesses a radius of curvature smaller than the adjacent eye wall. This distinct structural deformation is often considered the hallmark of pathological myopia.
Histological examination shows marked thinning of the sclera and disorganization of its collagen fibers, contributing to the progressive nature of the condition. The choroid, the layer of blood vessels beneath the retina, also becomes significantly thinner, especially at the staphyloma’s edge. Local biomechanical factors and reduced scleral resistance are thought to play a role in its formation.
Posterior staphylomas are classified based on their location and shape, with the most widely used system recognizing ten types. Primary types are categorized by location, such as those occurring at the posterior pole, around the optic nerve (peripapillary), or involving the macula. Type I, a wide, horizontal oval outpouching at the posterior pole, is the most frequently observed type. This classification helps clinicians predict potential associated complications and monitor structural changes over time.
Visual Impact and Associated Complications
The structural distortion caused by a posterior staphyloma directly leads to secondary diseases responsible for severe and permanent visual impairment. The abnormal bulging stretches the overlying retina and choroid, making them vulnerable to tears, atrophy, and fluid accumulation. Eyes with staphyloma have a worse prognosis and poorer visual acuity compared to highly myopic eyes without this deformation.
One devastating complication is Myopic Choroidal Neovascularization (mCNV), where abnormal blood vessels grow from the choroid beneath the retina. The stretching and thinning of Bruch’s membrane creates defects that act as entry points for these new vessels. These fragile vessels often leak fluid or blood, causing rapid central vision loss and the formation of scars in the macula, the area responsible for sharp, detailed vision. Eyes with shallower staphyloma depth have shown a higher frequency of mCNV, suggesting the neovascular process may require some preservation of the underlying choroidal blood supply.
Myopic Macular Schisis (MMS)
Myopic Macular Schisis (MMS) involves a splitting of the retinal layers, often due to mechanical forces exerted by the vitreous gel or epiretinal membranes pulling on the stretched retina. The staphyloma’s concave shape exacerbates this traction, causing the delicate retinal tissue to separate and form fluid-filled pockets. The incidence of macular schisis is significantly higher in eyes with more pronounced staphyloma severity.
Retinal Detachment
If this traction progresses, it can lead to a macular hole, a full-thickness defect in the center of the retina, or progress to a tractional Retinal Detachment (RD). Retinal detachment is a true emergency, as the retina pulls away from its underlying blood supply, risking permanent blindness if not promptly repaired.
Detection and Monitoring
The identification of a posterior staphyloma is initially suggested through a comprehensive eye examination, including a fundus examination, but advanced imaging is necessary to confirm the diagnosis and map the extent of the deformation. Regular and objective monitoring is crucial because of the condition’s progressive nature and its association with a high risk of complications.
Optical Coherence Tomography (OCT) has become the gold standard for diagnosis and monitoring, particularly wide-field OCT, which captures a broad cross-section of the posterior segment. OCT is invaluable for visualizing the exact contour of the scleral wall and the relationship between the staphyloma and the overlying retinal layers. This technology is capable of detecting early signs of complications, such as the splitting of retinal layers (schisis) or the presence of fluid indicative of choroidal neovascularization.
In cases where the eye’s media are opaque, B-scan Ultrasonography or Magnetic Resonance Imaging (MRI) may be utilized. B-scan ultrasonography provides a cross-sectional view that can clearly delineate the size and depth of the staphyloma, especially when optical imaging is challenging. MRI is reserved for detailed, three-dimensional mapping of the entire eye shape. These modalities allow clinicians to quantitatively assess the staphyloma’s severity and accurately stratify the patient’s risk for developing maculopathy.
Management Strategies
Management of posterior staphyloma is primarily focused on addressing the sight-threatening complications that arise from the structural changes, as there is currently no standard, curative treatment for the staphyloma itself. The goal is to stabilize vision and prevent further degenerative damage to the macula.
For Myopic Choroidal Neovascularization (mCNV), the standard of care involves the use of anti-vascular endothelial growth factor (Anti-VEGF) injections. These medications are delivered directly into the eye and work by blocking the chemical signals that promote the growth and leakage of the abnormal blood vessels. Prompt Anti-VEGF treatment can effectively dry up the neovascular membrane and preserve central visual function.
Surgical intervention is required for structural complications, particularly Myopic Macular Schisis and Retinal Detachment. A pars plana vitrectomy is often performed to relieve the tractional forces pulling on the stretched retina. During this procedure, the vitreous gel is removed, and internal limiting membrane peeling may be performed to release the physical pull on the macula, allowing the retinal layers to re-appose. For complex retinal detachments, the surgery may be combined with techniques such as scleral buckling to physically support the eye wall.
Specialized or experimental interventions, such as scleral reinforcement procedures, have been investigated to mechanically stabilize the thinning sclera and potentially halt the progression of the staphyloma. These techniques involve placing a material or graft onto the posterior globe to provide external support to the weakened eye wall. While not universally adopted as a standard treatment, they represent ongoing efforts to address the underlying biomechanical defect.