Cancer can significantly affect eyesight through several distinct mechanisms. The impact is not limited to tumors starting directly in the eye; vision can also be compromised by cancers originating elsewhere, the side effects of necessary treatments, or the body’s immune response to a distant malignancy. Understanding how cancer interacts with the visual system helps patients recognize potential symptoms and seek timely intervention. Effects range from temporary blurriness and dry eyes to severe, permanent vision loss.
Primary Ocular Tumors
Cancers originating within the eye are known as primary ocular tumors. In adults, the most common type is ocular melanoma, which typically develops in the uvea (the middle layer containing the choroid, ciliary body, and iris). Melanomas in the choroid can physically displace the retina, causing symptoms like distorted vision, flashing lights, or floaters. Large tumors may cause an exudative retinal detachment, severely compromising sight.
Retinoblastoma is the most frequent primary eye cancer in children, starting in the nerve cells of the retina. Its growth directly damages the light-sensing cells. A common sign is leukocoria, a white reflection in the pupil often noticed in photographs. If the tumor progresses, it can destroy the retina, leading to vision loss and potentially spreading along the optic nerve.
Metastatic Impact on Vision
A common way cancer affects vision is through metastasis, where cancer cells travel from their original site to the eye or surrounding structures. The choroid, the most vascular part of the eye, is the most frequent site for these secondary tumors, often originating from breast or lung cancer. Choroidal metastases cause blurred vision or decreased visual acuity, and frequently lead to secondary retinal detachment due to fluid leakage.
Cancer can also spread to the orbit, the bony socket surrounding the eyeball. Orbital metastases may cause the eye to bulge forward (proptosis) or restrict eye movement, resulting in double vision. When cancer spreads to the brain, tumors near the visual pathway (optic nerve, optic chiasm, or visual cortex) can compress these structures. Pressure on the optic nerve can lead to a rapid decrease in sight, while tumors in the visual cortex might cause specific blind spots.
Vision Changes from Therapy
Vision problems are frequently a side effect of cancer treatments. Traditional chemotherapy agents can cause ocular toxicity. Some drugs, such as cisplatin, are associated with neurotoxicity that manifests as optic neuritis (inflammation of the optic nerve). Other chemotherapy drugs commonly cause surface issues like severe dry eye, conjunctivitis, or corneal damage, leading to discomfort and blurry vision.
Radiation therapy directed at the head or neck can damage sensitive eye structures. Damage to the lens accelerates the formation of cataracts, which cloud vision. Damage to retinal blood vessels can lead to radiation retinopathy, involving vessel leakage and closure, resulting in vision loss months to years after treatment.
Newer targeted therapies and immunotherapies can also trigger inflammatory eye conditions. These agents may cause uveitis (inflammation of the middle layer of the eye) or serous retinopathy, where fluid accumulates beneath the retina, both leading to blurred vision.
Indirect Effects of Cancer on Sight
Cancer can indirectly affect vision through systemic complications, beyond the direct presence of tumors or therapy side effects. The most recognized indirect effects are paraneoplastic syndromes, which are rare disorders triggered by the body’s immune response to a distant tumor. Cancer cells produce antigens that provoke an immune reaction, and the resulting antibodies mistakenly attack similar, healthy proteins in the eye.
Cancer-Associated Retinopathy (CAR) is a paraneoplastic syndrome often linked to small-cell lung cancer. Autoantibodies target retinal proteins, attacking the retina’s photoreceptor cells. This causes symptoms such as photopsias (flashing lights), progressive night blindness, and reduced central vision. Additionally, severe systemic depletion (cachexia) associated with advanced cancer can lead to nutritional deficiencies, such as a lack of Vitamin A, impairing the eye’s ability to process light.