Ocular clues to occult malignancy: Can visual changes serve as early biomarkers of cancer before clinical detection?

Cancer is most curable when it is smallest, yet the majority of solid tumours are still discovered only after they declare themselves through mass effect, systemic illness, or incidental imaging. The eye offers a quietly remarkable alternative: it is the only site in the body where neural tissue, its blood supply, and the microvasculature can be inspected non-invasively, in vivo, and at subcellular resolution through an ordinary dilated fundus examination. This narrative review explores how visual symptoms and ocular signs—paraneoplastic retinopathies, distant metastases to the uveal tract, neuro ophthalmic syndromes, and so-called masquerade phenomena—may precede the clinical detection of an underlying malignancy, sometimes by months or even years.