Understanding Subretinal Hemorrhage
Subretinal Hemorrhage (SRH) is a serious eye condition characterized by the accumulation of blood beneath the neurosensory retina, the light-sensitive tissue lining the back of the eye, occurring in the space between the neurosensory retina and the retinal pigment epithelium (RPE). The RPE is the layer responsible for supporting the overlying photoreceptor cells. The proximity of the hemorrhage to the macula, the center of the retina responsible for sharp, detailed central vision, makes this an urgent matter.
Patients experiencing SRH often report an acute and sudden decline in central vision, which can manifest as a blind spot, or scotoma. The blood can cause irreversible damage to the photoreceptors through mechanical separation of the retina from its blood supply, iron-induced toxicity, and the creation of a physical barrier preventing necessary nutrients and oxygen from reaching the outer retinal cells.
The most frequent underlying cause for SRH is exudative, or “wet,” Age-Related Macular Degeneration (AMD), which involves the growth of abnormal, fragile blood vessels known as choroidal neovascularization (CNV). These new vessels grow from the choroid beneath the RPE and are prone to leakage and rupture, leading to the sudden onset of bleeding. Other, less common causes of SRH include conditions like retinal arterial macroaneurysm, ocular trauma, and Polypoidal Choroidal Vasculopathy (PCV), a variant of CNV.
How Optical Coherence Tomography Works
Optical Coherence Tomography (OCT) is a non-invasive imaging technology that has revolutionized retinal disease assessment. Functioning like an optical analogue to ultrasound, OCT uses light waves to create detailed cross-sectional images of the eye’s internal structures. It employs low-coherence interferometry, measuring the echo time and intensity of light reflected from different tissue layers within the retina.
The OCT device emits a beam of light, typically in the near-infrared spectrum, and then measures the back-scattered light from the various layers of the retina. Different tissues reflect light differently; for instance, dense structures like the nerve fiber layer and the retinal pigment epithelium reflect a strong signal and appear bright white or hyper-reflective on the scan. Conversely, clear fluids or non-scattering tissues like the vitreous appear dark or hypo-reflective.
By compiling these light reflections, the OCT system generates a high-resolution, layered image that allows clinicians to visualize the retina’s microscopic architecture. This enables the precise localization of pathology within the different retinal strata. The non-contact nature of the scan makes it a rapid and painless procedure, providing immediate diagnostic information without the need for injectable dyes.
Interpreting OCT Findings in Subretinal Hemorrhage
OCT provides information about subretinal hemorrhage unattainable through standard fundus examination alone. On a scan, the acute blood collection appears as highly reflective material, often called subretinal hyper-reflective material (SRHM), positioned between the neurosensory retina and the RPE. This dense material causes “shadowing,” where the strong reflection prevents light from penetrating deeper, obscuring the underlying choroid and RPE layer.
OCT precisely determines the anatomical location of the blood, differentiating between subretinal and sub-RPE hemorrhage. Blood in the sub-RPE space typically elevates the RPE layer, forming a hemorrhagic Pigment Epithelial Detachment (PED). Hemorrhage confined to the subretinal space, above the RPE, carries a poor prognosis for the overlying photoreceptor cells.
The OCT scan also enables the measurement of the hemorrhage’s thickness and lateral extent, which are factors that directly influence the likelihood of a positive visual outcome. A thick, large hemorrhage that covers the fovea is associated with a greater risk of permanent photoreceptor loss. Furthermore, the OCT often helps identify the source of the bleeding, such as an underlying CNV membrane, which may appear as an area of irregular, moderately-to-highly reflective tissue either beneath or above the RPE layer.
Current Management Approaches
The treatment strategy for subretinal hemorrhage relies on diagnostic details provided by the OCT, particularly the size, location, and underlying cause. For small, peripheral hemorrhages not involving the central macula, careful observation may be warranted. However, most fovea-threatening SRH requires prompt intervention to mitigate the toxic effects of the blood on the photoreceptors.
The primary pharmacological approach involves anti-vascular endothelial growth factor (Anti-VEGF) medications, injected directly into the vitreous. These injections aim to shut down the underlying CNV, typically the source of the bleeding, preventing further hemorrhage and promoting fluid reabsorption. Anti-VEGF monotherapy is a common first-line choice, especially for smaller or less severe cases.
For large, thick hemorrhages threatening the macula, treatment often incorporates pneumatic displacement (PD). This procedure involves injecting an expansile gas (e.g., C3F8 or SF6) into the vitreous cavity, often combined with recombinant tissue plasminogen activator (tPA). The tPA is a clot-dissolving agent that liquefies the dense blood clot, while the gas bubble physically pushes the liquefied hemorrhage away from the foveal center. The patient must maintain a specific head position for several days to ensure successful displacement.
Surgical intervention, specifically pars plana vitrectomy (PPV), is reserved for the most massive, thick, or persistent hemorrhages, or when pneumatic displacement fails. During a vitrectomy, the surgeon directly injects tPA into the subretinal space, followed by an expansile gas to displace the blood. This invasive approach allows for direct clot management, but it carries a higher risk of complications and is only pursued when the benefit of preserving central vision outweighs the surgical risks.