Radiation retinopathy is an eye condition involving damage to the retina, the light-sensitive tissue at the back of the eye. This damage results from exposure to ionizing radiation, typically as a side effect of radiation therapy for cancers located in or near the head and neck, brain, or directly in the eye, such as ocular melanomas. The condition can lead to various visual disturbances and, in some instances, severe and permanent vision loss.
How Radiation Affects the Retina
Radiation retinopathy develops when radiation therapy damages the blood vessels and nerve cells within the retina. Ionizing radiation directly injures the endothelial cells lining the retinal blood vessels, leading to their dysfunction or destruction. This cellular damage can trigger an inflammatory response, oxidative stress, and the release of pro-inflammatory cytokines, further compromising the retinal microenvironment. The initial damage often results in vascular occlusion and ischemia, meaning reduced blood flow and oxygen supply to parts of the retina.
Over time, this process leads to structural changes in the retinal blood vessels, including outpouchings, telangiectasia (dilated blood vessels), and microaneurysms. As endothelial damage progresses, these changes can result in capillary narrowing or closure, leading to areas of non-perfusion where blood flow is completely blocked. Radiation retinopathy is associated with external beam radiation therapy, plaque brachytherapy, and proton beam therapy. The likelihood and severity of the condition are influenced by the total radiation dose, the size of individual radiation doses (fraction size), and the specific area of the eye or surrounding tissue exposed. For instance, doses above 45 Gy are more frequently linked to its development, though it can occur at lower doses, sometimes as low as 15 Gy.
Identifying the Symptoms
Individuals with radiation retinopathy may experience visual symptoms that often appear gradually, months to years after radiation exposure. The onset typically occurs between 1.5 to 3 years post-irradiation, but can range from one month to 15 years. Blurred vision is a common initial symptom, which can progressively worsen.
Other visual changes include floaters, which are small specks or strands that drift across the field of vision, and distorted vision, where straight lines may appear wavy or bent. In more severe cases, individuals might also experience pain or redness in the affected eye, though these are less common initial symptoms. Because symptoms can be subtle and resemble other eye conditions, a thorough evaluation is important for accurate identification.
Diagnosis and Treatment Options
Ophthalmologists employ several diagnostic tools to identify radiation retinopathy. A comprehensive eye exam is the initial step, followed by specific tests to visualize the retina and assess its health. Fundoscopy, an examination of the back of the eye, allows doctors to look for characteristic signs such as microaneurysms, retinal hemorrhages, hard exudates, and cotton wool spots.
Optical coherence tomography (OCT) provides high-resolution images of the retinal layers, helping to detect swelling, particularly macular edema, and other structural changes. Fluorescein angiography involves injecting a fluorescent dye into the bloodstream and taking photographs as it circulates through the retinal blood vessels. This test is useful for identifying areas of blood vessel leakage, capillary non-perfusion (areas without blood flow), and the growth of new, abnormal blood vessels (neovascularization). These methods help differentiate radiation retinopathy from other conditions like diabetic retinopathy, which can have similar clinical signs.
Treatment aims to stabilize vision, reduce symptoms, and prevent further damage, as there is no method to reverse existing damage. Anti-vascular endothelial growth factor (anti-VEGF) injections are a common intervention, particularly for managing macular edema and neovascularization. Medications like bevacizumab, ranibizumab, and aflibercept are injected directly into the eye to reduce fluid leakage and inhibit the growth of new, leaky blood vessels. These injections target VEGF, a protein that promotes abnormal blood vessel growth and leakage.
Laser photocoagulation is another treatment option, used to seal off leaking blood vessels or destroy abnormal new vessels that could lead to complications like vitreous hemorrhage or retinal detachment. This procedure involves using a focused laser to create tiny burns on the retina. Corticosteroid injections or implants can also reduce inflammation and macular edema, often combined with anti-VEGF agents. While treatments help manage the condition and preserve remaining vision, long-term monitoring is required due to its chronic and progressive nature.