Subretinal fluid refers to an accumulation of fluid beneath the retina, the light-sensitive tissue at the back of the eye. This condition can significantly affect vision and often signals underlying eye diseases requiring attention.
What is Subretinal Fluid?
Subretinal fluid collects between the neurosensory retina and the retinal pigment epithelium (RPE). The RPE is a cell layer that acts as a barrier, regulating fluid and nutrient movement. Normally, the RPE pumps fluid away from the subretinal space, keeping the retina dehydrated for clear vision.
When this balance is disrupted, often due to a weakened RPE barrier, fluid leaks from the underlying choroid—a vascular layer—and accumulates. This accumulation can distort the retina’s architecture, interfering with its ability to process light and send clear images to the brain.
Underlying Causes
Several conditions can lead to subretinal fluid, each disrupting the eye’s normal fluid balance.
Wet Age-Related Macular Degeneration (AMD) is a common cause, characterized by the growth of abnormal, fragile blood vessels (choroidal neovascularization or CNV) from the choroid. These vessels leak fluid, including subretinal fluid, into retinal tissues, causing swelling and distortion of the macula. Vascular endothelial growth factor (VEGF) promotes this growth and leakage.
Central Serous Chorioretinopathy (CSC) also causes subretinal fluid accumulation due to leakage from the choroid through a weakened RPE. While mechanisms are not fully understood, it involves hyperpermeability of choroidal capillaries. Risk factors include emotional stress, “type A” personality traits, and corticosteroid use. CSC most frequently affects men between 30 and 50 years of age.
Diabetic Macular Edema (DME) results from damage to retinal blood vessels due to prolonged high blood sugar. Damaged capillaries develop microaneurysms and leak fluid, proteins, and lipids into the macula, causing retinal thickening and subretinal fluid. Breakdown of blood-retinal barriers, inflammation, and increased VEGF contribute to this leakage.
Inflammatory conditions, such as posterior uveitis, can also lead to subretinal fluid. Uveitis is inflammation of the uvea, the eye’s middle layer. In posterior uveitis, choroid and retina inflammation breaks down the blood-retinal barrier, allowing fluid to leak. This leakage is often driven by inflammatory factors, including VEGF.
Symptoms and Detection
Individuals with subretinal fluid may notice various visual symptoms. Common symptoms include blurred vision, distorted vision (metamorphopsia) where straight lines appear bent or wavy, and a blind spot (scotoma) or reduced central vision. Symptom severity varies based on fluid amount and location.
Detecting subretinal fluid and its cause requires a thorough eye examination. A dilated eye exam allows visualization of the retina. Specialized imaging tests confirm fluid presence and pinpoint its source.
Optical Coherence Tomography (OCT) is a primary diagnostic tool. It provides detailed cross-sectional images of the retina, visualizing and quantifying subretinal fluid, and assessing retinal thickness and structural changes.
To investigate leakage, fluorescein angiography (FA) may be performed. This test injects a dye into a vein, which circulates to eye vessels, highlighting leakage as a camera takes photographs. Indocyanine green angiography (ICGA) may also evaluate choroidal circulation, beneficial for diagnosing conditions like CSC. These techniques guide treatment by providing a comprehensive view of the fluid and its origins.
Managing Subretinal Fluid
Managing subretinal fluid involves strategies specific to the underlying cause.
For wet AMD and DME, anti-VEGF injections are a common first-line treatment. Medications like ranibizumab or aflibercept are injected into the eye to block VEGF, reducing fluid accumulation and stabilizing vision.
Photodynamic therapy (PDT) or laser treatment may be considered for chronic CSC or some forms of AMD. PDT involves injecting a light-sensitive drug, verteporfin, which concentrates in abnormal vessels. A low-power laser activates the drug to seal off leaking vessels. Conventional laser treatment can also seal off leaking blood vessels.
For inflammatory causes like posterior uveitis, corticosteroids are often prescribed. These can be administered via eye drops, oral medications, or injections to reduce inflammation and fluid leakage. In acute CSC, fluid may resolve on its own, and observation may be the initial approach.
Prognosis varies based on cause, severity, and timeliness of diagnosis and treatment. Early detection and intervention are associated with better visual outcomes and can help preserve vision. However, some conditions may lead to permanent vision loss if untreated, and recurrence is possible. Regular monitoring and adherence to treatment plans are important.