They can't see at all, but will argue that they can. In rare cases of stroke and brain damage, patients can lose their sight altogether. Disorientated and unaware of what’s happened, it can take clinicians days before they establish that the person has become blind. But what if the patient themselves don’t know that they are blind? In extremely rare circumstances, someone that has no sight at all will entirely believe, often to the point of anger, that they can see perfectly fine. With just 28 cases in recorded history, these people have been diagnosed with Anton syndrome. What is Anton syndrome? Anton syndrome, otherwise known as Anton’s blindness or visual anosognosia, is named after neurologist Gabriel Anton and describes someone that is cortically blind (blindness due to damage to the brain's visual region) but who confabulates visions that make them believe they have not lost their sight. They will adamantly claim that they are not blind and can see well, and will dismiss any evidence stating otherwise. Such patients often experience serious mental confusion and will try to mislead their caregivers by attempting feats that are difficult for a blind person to do, often stumbling over objects or trying to walk through closed doors. Soon, doctors and nurses may begin to suspect they cannot see, but helping them through their symptoms can be extremely difficult and distressing. It is especially common in elderly brain injury patients, further complicating the diagnosis and management, though it has been reported in a person as young as six years old. Anton syndrome was first described clinically by Gabriel Anton when observing a 69-year-old milkmaid, who had damage to both temporal lobes and was both deaf and blind. However, cases that could qualify as Anton syndrome have been documented as far back as the Roman times, when a woman called Harpaste became blind but staunchly believed she was not. She had attendants constantly changing the room as it was “too dark” and the entire ordeal was described in Seneca’s Moral Letters to Lucilius in 63 CE. Treatment focuses on the cause of blindness, which in the case of stroke patients is extremely limited. In some cases, multiple sclerosis (MS) has led to Anton syndrome, and drugs that alleviate MS did help one patient. Source
